I just thought it would be cool to get down to some of the subtle differences between the Renesis and the 13B engines. Everyone knows that the compression ratio is a little higher and that the Renesis has side exhaust ports but aside from that not too many people know much more. One thing I am going to leave out is the variable intake system.

The first thing I am going to get into is fuel economy as this seems to be a sore spot among owners. Hopefully you'll look at your engine a little differently after this. As we all know the Renesis makes much more power than any previous naturally aspirated rotary. The last naturally aspirated rotary of the same displacement was the 13B in the 89-91 RX-7. It made 160 hp. I don't care what everyone thinks their engine produces, even the low power engine can top 160!From a fuel consumption standpoint the Renesis is on average about 8% more fuel efficient than the 13B but as much as 15% in parts. Why then are RX-8 owners not getting any better mileage than the average RX-7 owner? 2 reasons. The first is that you have a 4.44:1 rear end ratio whereas the RX-7 had a 4.10:1. Lower yours to a 4.10 and you'll see a little improvement. The other reason is that the RX-8 is at least 300 lbs heavier (and in some cases depending on model comparison, much more) than the RX-7's were. Weight and gearing are holding you back from noticable improvements. You guys that complain now know what to do so do it or put up with it.

The side exhaust port led to many improvements (all of them!) over the 13B. The first of which is the fact that the Renesis no longer has any port overlap. This is the point in the rotation of the rotor where the intake and exhaust ports would simultaneously be opened at the same time. The Renesis does not have this but all of the 13B's did. The port overlap of the peripheral exhaust port rotary caused unstable combustion at low engine speeds and loads and this meant that the older rotaries had to run richer than the stoich a/f ratio in those ranges to run properly. This led to worse fuel economy than in the Renesis.

The side exhaust ports also did something else very important. It allowed the closing point to occur later, right around exhaust TDC. The exhaust closes at 3 degrees BTDC (Before Top Dead Center) to be exact. Having 2 of them per rotor made the total area 47% larger than the single peripheral exhaust port of the 13B. The 13B exhaust port closed later at 48 degrees ATDC (After TOP Dead Center)! There are 2 important things about this. The first of which is that there can now be changed intake port shapes to make them larger and still not have any port overlap. The second thing is that the 13B exhaust ports had a much longer expansion stroke. The exhaust ports opened much earlier on the old engines. Some RX-7 people seem to think that this means that it has much more time to get the exhaust out and it should do it under less total pressure. Wrong!!! A long expansion stroke is unfavorable in terms of thermal efficiency. Heat is energy that can work too and the Renesis uses it better. The proof of this was already mentioned in the fact that the Renesis has an 8-15% improvement in fuel consumption. People can argue this all they want but power levels also prove it. As some may have also noticed, this added heat from the Renesis is also murder to a cat. There are more cat failures on the RX-8 than there were on the RX-7. Now you know why!

On the intake side, the Renesis intake ports are 40% larger than those in the 13B. Again made possible by the side exhaust port layout removing port overlap. As an example of how this has happened, the primary ports of the Renesis open at 3 degrees ATDC while the 13B ports opened at 32 degrees ATDC. That's 29 degrees more of open time. The Renesis ports also close at 65 degrees ABDC (low power at 60 ABDC) while the 13B primaries closed at only 50 degrees ABDC. That's 15-20 degrees more on the closing side as well. Unlike a piston engine we can not keep total opening size the same if we change the timing. On a piston engine this would be done by simply changing the valve lift. The rotary has the piston equivalent of changing both lift and duration.

Opening the intake ports earlier had a big effect on a different aspect of the engine. That was the side seals. On the older rotaries, when people opened the intake ports too early, they risked both having a corner seal potentially fall into the intake port but also from having the side seal edge crash into the closing edge of the intake port. The Renesis has something very subtle to try to alleviate these issues. The side and corner seals are moved outward on the rotor by 2mm. I have seen people ask how hard it would be to modify a 13B rotor to work in a Renesis. This is one big issue but I'll get into the others.

A cutoff seal was also added to the Renesis rotor between the side seals and the outer most oil control ring to prevent any port overlap on the sides of the rotor. Without this ring, a small amount of exhaust gasses could actually get around the side and mix with the intake. So much for no overlap. The cutoff seal took care of this. The shape of the side seals is interesting as well. It is a wedge shape. This is to help remove any carbon from building up in the groove which would cause it to stick. Carbon is also the reason for the interesting shape of the Renesis exhaust ports as well as the overly large seal clearances in the Renesis over the 13B. And some of you thought carbon was related to synthetic oils! Shame on you! That was actually the reason why we haven't seen a side ported rotary until the Renesis. Back in the '70's Mazda did try the side exhaust port and back then they also found it to be superior. The problem was the carbon would cause seals to stick and break. You can't market that. They met the standards of the time with the peripheral exhaust port so that's what they stuck with.

The rotor shape has changed slightly as well too. It is very subtle but the 13B rotors are more "round" while the Renesis rotors are more of a true "triangle" shape. Hopefully you can figure that one out. Another very small difference and this one is real small is the rotor width. Yes there is a difference! The rotor housings are not any wider though so you don't get any added displacement. To minimize the hot gasses that could come around the sides of the rotors, the clearance on each side has been decreased an average of 18%! The 13B has more clearance than the Renesis does. Race engines add more clearance yet. This was always an issue at higher rpms over 8000 as there was the possibility that the rotors could actually come into contact with the side housings. You have a higher revving engine with less clearance! Why? Your rotors are lighter and better balanced, your bearings are better, and your eccentric shaft is lighter and stronger (more rigid). Don't sweat it.

What about compression? Well as we all know it went up from 9.0:1 on the previous RX-7 (turbo) and 9.7:1 on the last naturally aspirated rotary to 10.0:1 on the RX-8. Years ago Mazda found that there was no appreciable difference in power on a naturally aspirated rotary with compression ratios from 9.0:1 up to 11.0:1. Virtually no power difference. So why then would they do it? Emissions! Yes, emissions. I know that doesn't make much sense. Remember that although the engine has no port overlap, there is still a small space in the rotor face that some unburned air gets carried back into the intake side in. By raising the compression ratio, they made this area slightly smaller. This does a better job at minimizing the containment volume of the exhaust gasses at closing timing and reduces the need for exhaust gas recirculation. This results in improved combustion stability at low engine speeds and loads. I know many would like lower compression ratios for boosted applications but emissions comes first to Mazda. Boost is for you to work out!

I'm going to skip going over the intake system and the anti wet port jet air/fuel system.

On to apex seals... The old apex seals were 3 piece from the factory but 1 and 2 piece were available from the aftermarket and were even types that once appeared on much older engines. These seals had a total height of 8 mm. The Renesis apex seals are 4.5 mm tall and are 2 piece. That's it. A lighter apex seal can seal better with less spring pressure at higher rpms which improves efficiency and decreases wear. As a result of this decrease in wear, the Renesis does not need as much oil injection as the 13B did. The dual oil injector placement in the rotor housings also allows more even distribution of the injected oil in the engine. A downside to the lighter apex seal is that it is easier to succumb to flooding! The rounded shape of the seal tip allows gasoline to get under it. As it rotates and tries to compress the air, this added pressure will also be in the gasoline under the seal. This will exert pressure on the apex seal trying to push it into it's groove. If it does this, pressure will bleed from one chamber to the next which lowers compression. The fact that any fuel in the engine doesn't leave as easily out a side exhaust port as it does a peripheral one doesn't help matters either. That's the best explanation I can give any of you as to why your engine floods.

It's 3:30 am right now and I'm damn tired so I'll leave with one more thing and add more details to this tomorrow. Your corner seals have a coating on them which Mazda refers to as DLC. I'm too tired to go look it up right now. That makes them very hard. It has been reported that when used in Renesis rotors in older 13B engines, these seals absolutely will tear up a 13B housing. This means the Renesis housings must also have a coating on them which is much tougher. More on the engine later. I'm sure a few others who know some other small things will have contributed by then.

That's all for now.

Thanks for the excellent info!

Just curious, where did you get this info from?

Thanks,

Anthony

Thanks for your labor!. When you are rejuvenated can you go into the DLC. What is it composed of? Is it something Mazda developed or borrowed from another industry?

I understood that Mazda developed a technique for cutting micro fissures :Eyecrazy: into the surface of the housings, in an effort to form a circumferential oil film, but I've never heard whether this technology made it to the final production Renesis.

Can you shed any light on the process and it's application?

S

I hate you RG ! I HATE YOU !

I await more rotary knowledge. RG is the best!

Thanks for the excellent info!

Just curious, where did you get this info from?

Thanks,

Anthony
It's information that I've built up over the years from reading books, talking to people, studying actual parts, personal experience, as well as getting ahold of some good SAE papers. I'm just trying to put it all together in one spot. I'll slowly add more as I think of more.

RG and I have built a collection of SAE papers on the Rotary and Renesis engine. Alot of interesting info in there, that had I known a few years ago, would have answered some questions that have been forum debated until recently.

Having friends in Ph.D engineering programs is nice, I get access to the SAE database.

The Renesis Engine is truely a leap over the old 13B.

The reason most folks don't see the performance is that its having to lug around a heavier car and Mazda had to detune the engine for emissions reasons. In addition, it hasn't been as tuner friendly due to the ECU being such a bitch to work with.

Over time, as the Renesis becomes cheaper, 13B's will begin to fade away. IMO, there is simply nothing that a 13B does better than a Renesis for a street vehicle, other than cost less.

Thanks for your labor!. When you are rejuvenated can you go into the DLC. What is it composed of? Is it something Mazda developed or borrowed from another industry?
DLC stands for Diamond-Like Carbon. It is very hard but it is also very slippery. Nissan even uses this in their current 3.5L VQ35HR and 2.5L VQ25HR engines so it isn't only a Mazda coating.

awesome read, subscribes for future RENESIS enlightenment, ommmmmmmm

OK let's get on to the Jet Air/ Fuel Mixing system. This system is used primarily for decreased fuel consumption and emissions at idle speeds. This is located in the lower intake manifold and appears as small vacuum tubes inside the intake runners. They actually originate in the lower manifold but extend into the port runners in the engine housings. These tubes are nothing more than vacuum tubes which bypass the intake manifold. Air is sucked in these tubes at a slightly higher rate than the air in the manifold as there is a greater pressure drop in the manifold than there is in these bleed tubes. What these do is to create turbulence at the lower side of the intake runners right before they make the turn into the engine. Fuel is sprayed at this location in the housings and when the fuel comes into contact with this air, it atomizes better. Combined we call this the AWP or anti-wet port.

It sounds like a simple idea but how well could it possibly work? After all doesn't a small tube in the intake manifold mean less flow? Hydrocarbon emissions are lowered up to 30% at idle over the lack of this system so it is very effective at what it does. The added atomization also results in about a 7% decrease in fuel consumption at idle.

Just imagine how nice and slow and inefficient your RX-8's would be with the last nonturbo rotary! 160 hp at the crank, dirtier emissions and worse gas mileage. Gotta love the Renesis! It is superior to any rotary prior to it in every way.

Very nice, knowledge is power. Keep it coming.

I do have one questions. I had read some where that the turbo guys where speculating that one issue with turboing the RX-8 was the exhaust flow was restrictive. The RX-8 aving larger port openings would seem to make this a false statement but maybe there side placement is causing flow issues out of the combustion chamber. Any info you can add here?

Now let Mazda apply renesis magic to 12a's and bring back a newer cheaper better RX3.
How 'bout the mazda 3 with optional 12a renesis??

Logically you would think that a straighter exhaust path is better and should flow more. It should and the 13B exhaust ports probably do flow better if we are only going off of pure flow numbers each. However power isn't only determined by flow. (Don't tell the RX-7 people that!) Timing also plays a very important part as the old peripheral exhaust ports stayed open for too long which was inefficient use of heat. They also opened too early.

When the peripheral exhaust ports open, they are very sudden. It takes very little eccentric shaft rotation to open them fully compared to a side port. This means that the exhaust gasses leaving the engine do so much more abruptly. It is more of a shockwave. The rest of the port opening time isn't so much being used to expell any more exhaust gasses as most of them left right when the port opened. The total exhaust gas velocity peaks very early and then plateaus.

With the side exhaust port, the total port timing is much less. This isn't necessarily a bad thing though as the Renesis uses the total open time much better. The side ports open and close more slowly. In other words it takes mroe eccentric shaft rotation in order to fully reveal their total port area. This means that the gasses leaving these ports must speed up over a longer period of time. There is less of a shock wave type of pulse leaving them. Total flow is greater though as the gas velocity reaches a much higher peak speed than in the peripheral exhaust port. This helps leave a lower pressure in the combustion chamber which results in a cleaner chamber. There is always something left over though and even an engine running at 100% efficiency will still have 10% carried back to the next cycle.

The impact of the peripheral exhaust is what is so good for spinning a turbo. It isn't the total flow through the port itself as it pulses. The Renesis is more conventional and has exhaust pulses that more closely resemble those of a piston engine. It is still good for turbocharging though but the exhaust energy is very different.

Now it might sound like the impact is what we really want but remember that the max exhaust velocity out of the Renesis is greater than the 13B. There is also more heat in the system so the Renesis is still very good and capable at turning a turbo. It just does it in a different way. Mazda had to redesign their exhaust wheels on their turbos to take these sudden pulses into account. The blades were much more flat to absorb as much of the initial impact as it could as opposed to being more curved which favors the gentler exhaust profile of piston (and side port) engines.

RG's a friggin genius...

Score one for Houston...

Two for RG...

Nope, but I did stay at a Holiday Inn Express last night.

There is one thing I want to make very clear:

LONG LIVE THE RENESIS !!


Philip

Very Long

So in short the exhaust is more then adequate for turboing and given that the turbos being used are designed for piston engines they should work well with the RENESIS because of the similar exhaust signatures. This would lead me to believe that the main advantage that the RX-7 turbos had over the RENESIS for turboing is the lower compression ratio. I also wonder if the shared center exhaust port could be causing back pressure problems from one rotor to the next.

I hope these questions are still in the spirit of the original post, not meaning to hijack it but I find the comparisons of the two engines in the application very interesting.

The high compression is a issue for FI if your going to aim for boost levels above 1 bar (14psi). Not saying it isn't possible, but your tuning has to be very good if you want your engine to survive.

Lower compression gives you more margin for error, but I think people make it out to be a bigger deal than it needs to be for the majority of street FI applications. Our course there are people that will bitch b/c they want to build a 30psi 600HP monster engine that is reliable, but really how many people will really do that? 350 at the wheels will make this car a terror, and is easily achievable in a reliable package with proper engine management.

The center exhaust port shouldn't be causing back pressure issues between chambers since there is a divider between the two....I default to RG on this one as he knows more about that area.

For a turbo application it isn't an issue at all.

nice write rg!!!

thx.

beers :beer:

Weight and gearing are holding you back from noticable improvements. This following is the unfathomable part to me.

When I drive my 91 RX7 at 70mph in top gear (5th) the engine turns at 2800rpm.

When I drive my 03 RX8 at 70mph in top gear (6th) the engine turns at 3500rpm.

The Renesis has 20-30% (is that the right range?) more torque than the 13B and an extra gear, yet is running 25% faster at any given speed. That's not smart.

This is the only real problem I have with a great car, and it's a gear train complaint, not an engine complaint. I love the engine, especially the way it zzzzings at high revs...like a friendly chainsaw.

Mazmart sells a 4.10 rear end for the RX-8 if you are interested in changing it to be more comparable with the RX-7 gearing.

great info RG-- sounds like Mazda put a lot of effort and thought into R&D for this engine. I understand why they didnt put real gauges in this car but why the heck did they mandate 5W20 for all temp zones I will never know. Well I do know but it still doesnt make sense to me.
Keep the info coming--any benefit in the rotors from heat plating or blueprinting the leading edges?
Olddragger

good read, question though. Exactly what effect would direct injection produce compared to the current set up of the renesis?

Direct injection if implemented properly would mean better economy and emissions over the current engine and perhaps even some more power. I don't expect to see miracle power increases but everything helps.

A downside would be that due to very precise fuel metering, there is no aftermarket ecu out there right now that can control direct injection. You could not change anything until a flash was developed for it. In other words, no forced induction until after the ecu is figured out. Mazda has been working on DI for years. I suspect one day we'll see it appear on a production rotary as the engine isn't going away any time soon.

Too bad there isn't an easy way of changing out just the 6th gear ratio. All the other ratios are fine with me, but 6th is too short.

Very helpful info RG!! This info helps me investigate and improve the Renesis engine, so i can sell RX-8 engine kits and do some heavy porting on it.

/Lasse

Your corner seals have a coating on them which Mazda refers to as DLC. I'm too tired to go look it up right now. That makes them very hard. It has been reported that when used in Renesis rotors in older 13B engines, these seals absolutely will tear up a 13B housing. This means the Renesis housings must also have a coating on them which is much tougher.

This is why I worry about the prospect of getting a remanufactured engine. Is it possible, or even likely, that some of this coating would be machined away in a remanufactured engine?

This is why I worry about the prospect of getting a remanufactured engine. Is it possible, or even likely, that some of this coating would be machined away in a remanufactured engine?


nope that is the point of the recall....

beers :beer:

I'm a fan of this thread.

This is why I worry about the prospect of getting a remanufactured engine. Is it possible, or even likely, that some of this coating would be machined away in a remanufactured engine?
Nope. They use all new seals.

good read rg... this is what some of the 7 owners should read....

i hope i fail my compression test...haha

Nope. They use all new seals.

I think he may have meant the coating on the housing which would also be a concern of mine.

Kevin

I would think that Mazda would have the housings re-coated if it was really an issue. Do you think they'd really send out remanufactured engines that had this coating machined off after going through the trouble and spending countless amounts of money on the recall in the first place?

Also, I remember reading that housings are typically not machined. They are either able to be re-used or they're junked. I may be wrong, but that sounds right.

RG, do you know what the beginning of time was like? when the world is going to end? :lol: Thanks for all the info, explains a lot to all of us. I've actually been wanting to find out more about the engine (rotaries in general) and this actually helped a lot.

RG, do you know what the beginning of time was like? when the world is going to end? :lol: Thanks for all the info, explains a lot to all of us. I've actually been wanting to find out more about the engine (rotaries in general) and this actually helped a lot.

Have you been to any of the local club meets? We now have a northside meet. I'm in Spring.

I would think that Mazda would have the housings re-coated if it was really an issue. Do you think they'd really send out remanufactured engines that had this coating machined off after going through the trouble and spending countless amounts of money on the recall in the first place?

Also, I remember reading that housings are typically not machined. They are either able to be re-used or they're junked. I may be wrong, but that sounds right.
They don't recoat anything in a rebuild. They measure the wear on a used housing and if it is within spec, they still use it. That's it. The Nitride coating on the rotor housings is decently thick and most wear grooves are still within the thickness of the coatings. This is why some people say it is bad to resurface housings through lapping or grinding. Typically the process removes the coating completely. While this leaves a nice smooth housing, it also leaves it more prone to wear so it's a tradeoff. I keep planning to find out who can apply this coating to housings so you can resurface them and recoat them. I know who I can ask next month at Sevenstock so hopefully I can get an answer.

Have you been to any of the local club meets? We now have a northside meet. I'm in Spring.
I havnt, I need to update my location, I moved for college so now I'm actually over in san antonio =( maybe I could make it to a meet when I go home for the weekend or something.

They don't recoat anything in a rebuild. They measure the wear on a used housing and if it is within spec, they still use it. That's it. The Nitride coating on the rotor housings is decently thick and most wear grooves are still within the thickness of the coatings. This is why some people say it is bad to resurface housings through lapping or grinding. Typically the process removes the coating completely. While this leaves a nice smooth housing, it also leaves it more prone to wear so it's a tradeoff. I keep planning to find out who can apply this coating to housings so you can resurface them and recoat them. I know who I can ask next month at Sevenstock so hopefully I can get an answer.

RG here is a firm that does recoating.

http://www.jhbperformance.com/

I have not used their service myself but I hear the product is supposed to be quite good.

Chris...

Without going into too much detail let's just say that I refuse to give them any of my engine parts until they prove themselves in a little more consistent and reliable manner.

Without going into too much detail let's just say that I refuse to give them any of my engine parts until they prove themselves in a little more consistent and reliable manner.

Like I said, I wouldn't know since I haven't dealt with them...yet.

Of course they're a local firm so comments I have heard are favourable. Not having to deal long-distance & cross-border make life MUCH easier.

Have you had consistancy issues with their product? PM me if you don't want to post details.

Chris...

So, RG, it seems our conversations and speculations from 2 1/2 years ago (when I was pondering nitrous use) have proven true in that we both suspected that Mazda HAD to have made improvements over the old 13B when they released the Renesis. It was the conclusions you and I came to that empowered me to embark on the nitrous project. Thanks for the detailed info on WHY this engine is far more accomodating to the abuse I have subjected it to when compared to previous versions of the rotary engine. 11,000 rpm's, nitrous use during the fuel cut, and several episodes of knocking/detonation, and it still runs like a Swiss watch.

this is general rotary tech not renesis specific- but two of the "problems" with rotaries hav ebeen low Torque and innefficiences related to the combustion chamber shape. digging through some things to find the geometry associated with sizing of rotaries reminded me i have been thinking how to change the various dimensions to overcome the issues.

first T. the T is "small" because the "length" of the "lever" creating that T is short. is there a way to increase the internal or external diameter of the rotors to inpart a greater force on the eshaft without detrimetnal effects in longevity or efficiency?

efficiency- shape of the combustion chamber is too long for really efficient combustion- flame front propagation etc. would widening (adding displacement)the rotors to create a more square chamber create a more efficient rotary or would the added displacement offset the gain? would widening but shortening to create a more square chamber of the same displacement work better?

just a couple of the thoughts racking my brain through the average day.

Torque is a function of displacement. The rotary has very little displacement so torque will always be low without added help. If we were to change the "stroke" of the engine but adjust other dimensions so the total displacement didn't change (narrow the rotor width), torque should not change in terms of overall peak but rather in terms of where it occurs in the powerband. The greater the stroke, the lower the torque peak. On a stroked piston motor, we tend to see everything go up but remember when they add stroke to those motors, they also add displacement. If they were to add stroke but decrease bore to keep the engine the same total size, peak torque would not change appreciably but the rpm it ocurred at would. A short stroke motor has a torque peak higher in the powerband.

As far as widening the rotors, we'd need to reduce the "stroke" of the motor to keep the displacement the same. That would be less efficient down low and would need higher rpms to get to it's best power. Narrowing the rotors would need increased stroke to keep displacement the same. It would be more efficient down low but not as high up top. When displacement remains constant, it is a balancing act to decide which combination will yield the best overall compromise for the engine's intended use. While a more square rotor face may be more beneficial from a fuel combusting standpoint (it may not though), the difference in stroke may offset this so may not be able to use it to any advantage.

so lets increase the displacement by making the camber wider and therefore more square. or enough to make it exactly square. does the increase in displacement offset the gains? i cant find any information that this has been done and the results good or bad. maybe someone at 7stock will be able to answer. ill have to get the question translated to japanese probably.

I am not a fan of making the rotor any larger as it has several issues to overcome. The first of which is that we can not make our ports any larger to give us the needed airflow up high. They would be large enough to supply air for a lower powerband but if this mean that we weren't getting any more power out of it, no one would be happy with it. The other issue is that a larger chamber would mean a larger area for the flame front to travel and this would result in lower efficiency and worse emissions as a result.

My choice would be to use a 3 rotor that is smaller in every way but of the same total displacement as the current 2 rotor.

i just remembered reading something recently suggesting the larger square rotor would not have the same flame front issues. wish i could find it now

What are the draw backs of going 3 rotor with the same displacement?

I ask because I wonder about the possible reasons Mazda has not done this already.

as i thought agoogle of the relative terms now does not find the article i previously read.

however- so a 3 rotor of the same displacement but with more square combustion chambers? increase the available torque and increase the efficiency?

come to think of it - was it Richard that said something about combustion chamber shape?

While I do remember the advantges of the side exhaust RG stated earlier in other threads.

As we all know, the peripheral port exhaust setup will never pass emissions (ie. older 13Bs), I think that is the main reason why we have our current setup in the Renesis. But however, with Direct Injection technology in the Renesis, could we stick with the side intake and go with peripheral exhaust once again?.

With DI, most (if not all) of the fuel will be burned during combustion. And no unburned fuel will be swept out of the pport exhaust. Is there power to be had with this setup? This might introduce overlap and other disadvantages of the older 13Bs, but it seems like the side exhaust is really limiting power output, and I know for a fact that in race engines, pport intake and exhaust is best for power.

Now the problem with this is I am not sure if ALL the fuel will be burned with DI in a rotary engine combustion chamber.

If this works, it is much easier to make a 1.3L 3-rotor than Renesis based(side intake+exhaust) 3-rotor.

edit: Maybe you could slap an extra spark plug in too, however that'll never happen from the factory , 3 per rotor.
________
AllDayFunnn (http://www.girlcamfriend.com/cam/AllDayFunnn/)

What are the draw backs of going 3 rotor with the same displacement?

I ask because I wonder about the possible reasons Mazda has not done this already.


my guess is this: The current design of Mazda's rotary engines are heavy (due to the iron-aluminum sandwich). One, you'd be increasing the weight of the engine significantly. Two, rotary engines are not very efficient, due to the design. So adding an extra, inefficient rotor, seems to me like it would just further reduce the fuel efficiency. It's hard enough to sell the current fuel efficiency.

I would like to build a 10A based 3 rotor though, just because. People always want the max power out of their cars, I just like a little oddity and sideways thinking. It'd probably sound pretty cool too. Maybe slap it in an old Volvo...hmm :)

There were many compainies back in the late 50's / early 60's that bought into the Wankel experiment and a vast amount of data and configurations were tried. Some were quite large. I have a book that talks about all the phases that it went through, from Wankels days with valve train work in the 20's up to 1998 and it even has some things about the then prototype RX8.

Allis chamers was heavily working the Wankel and did some of the best work on many fronts. I understand that the final dimensions are set within rather narrow parameters for the motors to work with any effieciency and reliability. Size is scalable but the relationships within the motor are not easlily changed. More than 2 rotors causes significate issue for the main shaft as it has to be made in two-pieces after two rotors right ?!?!

Wankel original design is not even what we have today since 1958 as the Wankel. The original was a true rotary spinning up to 25k with two housings and the carburator and spark plugs deep inside the motor. I believe it was an engineer that he worked with that changed it to the current base design so the could more effienently get the power off the rotating member.

I actually did a report paper for it at school in 10th grade with a mathematical calculation demonstration but I got an F because the teacher said I cheated and used someone elses work, that I couldn't understand it myself. Well that's not true but I can drive the hell out of it when my dad let's me.

I have an ISBN for the book if anyones interested, not sure where we got it but it is quite complete with lots of drawings and explainations etc.

Great,
Jeff B.

id love to take a look at that book. whats the isbn?

OK, I will post it but I'm at the Univ. in minneapolis now so I will have to call and get it from home. Check back tomorrow latest, it will be here. Maybe I will get a picture of the front cover too. We got it off Amazon i'm sure, in the spring of 2004.

Great, Jeff B.

Gee, I'm sure Mazda has not considered all the ideas posted before. I know they only spent $20.00 on rotary research. Damn amazing they got the HP they did with no FI in the 8. They are probably tying to improve both HP and fuel economy, and hopefully will see some results in the next 2-3 years. Turbo? yea, thats why the old 7's got such a bad rep, they blow the seals, if they come up with something reliable I'm sure they will sell it. Never buy a tubo'd car used, it was abused:)

"Hats off gentlemen - a genius."



- Robert Schumann on first hearing a young Chopin

"Hats back on gentlemen - an idiot."



- Robert Schumann on first hearing P.D.Q. Bach


- MazdaManiac upon reading post #59 in this thread.

... there is no aftermarket ecu out there right now that can control direct injection. You could not change anything until a flash was developed for it. In other words, no forced induction until after the ecu is figured out. Mazda has been working on DI for years. I suspect one day we'll see it appear on a production rotary as the engine isn't going away any time soon.Been a few times to *** in Germany for EFI Technology (the European company, not the Inc.) tech support on the following engines : VW 2.0 TFSi (direct injection, turbo, VVT) and VW 1.4 TSi (direct injection, supercharger and turbocharger, VVT) running from an aftermarket Euro-12 ECU. Works fine. Controlling the injectors is not a real problem. It's the high pressure fuel pump that's a bit of an issue, especially as the change from engine to engine (2 lobes, three lobes...). Special hardware and software, but nothing an up-to-date ECU development company can't get sorted out.

I guess the main issue with DI in a rotary is the fact the combustion chamber moves so much. Difficult to perfectly control the mixture and ensure ignitability in all speed and load conditions. The extra hole in the housing might also reduce fuel economy (due to leak over the apex seal from the high pressure combustion side to the lower pressure compression side).

And on a side note : more threads like this please!

Fabrice

OK, here is the ISBN on the Wankel book.

ISBN 0-7864-1177-5

The Wankel Rotary Engine.

(Picture of cover below.) And it was Curtiss-Wright not Allis-Chambers as a huge developer of rotary technology in the early days with Germany's NSU where Wankel himself worked. (circa 1959 -1966) Curtiss-Wright built a 1920 cu in. monster wankel motor that made 872 hp. They built the first multi rotor unit and everything in between including ones that ran on every concievable fuel of the day.

Great,
Jeff B.

I've got that book.

And I just ordered it. :)
Hope it's worth the money.

Yea, it is a great rotary reference and history that is fact based. I didn't read any others that were as concise. Hope other will find it a help.

Great,
Jeff B.

Rotarygod, I'm new to rotaries, to the RX8, and to this board. I thank you for this and other posts that have contributed to to my knowledge base on the subject.

Your posts bring a couple questions to mind, both about apex seals. Bear with me on one one question, please, as I try to apply a little of what I know about piston engines here (my piston experience is with Harleys). I hope that won't get me banned. :Peace:

The non-piston question is this: The apex seals are subject to a high degree of centrifugal force as the rotor spins, or so I would suspect. Does this have any effect on seal-to-wall scraping pressures, and thus on wear rates of the seal as RPM increases? Or are they held tightly captive in their grooves? Knowing that springs are under them makes me think they are not held tight.

Next question, and it's sorta complex.

The oil scraper ring groove on a lot of pistons is perforated so that crankcase pressure can vent through the piston wall to behind the ring and press it out against the cylinder wall, increasing the effect of the scraper ring.

Now, taking that concept and applying it to a rotor. My limited understanding of how these things work, and my reading here and around, indicates that gas escape past the apex seal into the following chamber is an issue in rotary engines for several reasons.

To your knowledge, has Mazda ever tried venting the leading edge of the rotor into the apex seal groove so that the pressure of combustion gases push the seal out against the chamber wall? Seems to me that it might work, but if they haven't done it there must be a reason.

Thanks,

Pilgrim

The apex seals can move around ever so slightly from side to side in their grooves. At low rpm's the seals need the apex seal springs to hold them against the housings. At high rpm's, centrifugal force does it. Chamber pressures hold the apex seals towards the back of the grooves. Remember that a piston ring goes back and forth in relation to it's orientation. An apex seal is constantly trying to be pushed out of it's groove due to it's orientation in relation to movement. Fortunately the rotor housing is there so it can't. Centrifugal force holds our seals against the sealing surface. Yes the faster the engine spins, the faster the seals wear themselves and the housings. This is why we have oil injected into the engine. It's to lubricate these surfaces.

Ceramic apex seals are not as hard on rotor housings for 2 reasons. The first is that they are naturally very slippery and don't absolutely need as much lubrication to move freely. This is less friction. The other reason is that they are lighter. At high rpm's, they don't exert as much force on the housings but they still seal as well if not better. So how can they seal better if they are lighter? At high rpm's, apex seals may chatter due to improper lubrication. This is when they in essense skip repeatedly over the surface. This leaks some pressure but also will eventually wear ridges in the housing. The ceramics don't do this. The more time they are on the surface, the better they seal.

Question, if the apex seals may clatter at high rpms, could that be a possible reason for the marbles in a can sound of some of the members here? I'm not saying it is, but is it possible or does it not sound like that?

You can't hear it.

At high rpm's, centrifugal force does it. Chamber pressures hold the apex seals towards the back of the grooves.

Yes the faster the engine spins, the faster the seals wear themselves and the housings.

Ceramic apex seals are not as hard on rotor housings . . . At high rpm's, apex seals may chatter due to improper lubrication.

Thanks, RG; great info.

New question: If I knew how to calculate the circumference of an epitrochoid I could figure out the answer, but I don't, so - any idea what the rotor speed (equivalent to piston speed) is at 9k RPMs? That's just about THE major factor in cylinder survival in a piston engine. Is it so in a rotary?

Pilgrim

OK, here is the ISBN on the Wankel book.

ISBN 0-7864-1177-5

The Wankel Rotary Engine.

(Picture of cover below.) And it was Curtiss-Wright not Allis-Chambers as a huge developer of rotary technology in the early days with Germany's NSU where Wankel himself worked. (circa 1959 -1966) Curtiss-Wright built a 1920 cu in. monster wankel motor that made 872 hp. They built the first multi rotor unit and everything in between including ones that ran on every concievable fuel of the day.

Great,
Jeff B.

Just placed my order for the book as well.

The rotors spin at 1/3 the speed of the eccentric shaft. Their speed does not remain constant though. The rotors depending on where they are in the housings, speed up and slow down in relation to the housings. Apex seal speed across the housing surfaces is not constant.

Survival of a rotary is dependent on 2 main things. The first is bearing life. The engine only has 2 bearings supporting the eccentric shaft front to back. The intermediate housing does not have a bearing for support. At high rpm's this can lead to eccentric shaft flex. That takes us to our second problem.

If the eccentric shaft flexes too much, the rotors can physically come into contact with the side housings, damaging them. Race motors usually run more side clearance to help reduce this risk. Fortunately there is something that can be done which takes care of both issues at the same time.

Add a center bearing. Guru Racing out of New Zealand (I think?) makes custom eccentric shafts and can install a center bearing in the engine. This reduces flex on the eccentric shaft but also adds another bearing which gives you 50% more total area than stock. This one mod alone can do wonders for engine life at higher rpm's, including helping it to make more power.

The rotors spin at 1/3 the speed of the eccentric shaft. Their speed does not remain constant though. The rotors depending on where they are in the housings, speed up and slow down in relation to the housings. Apex seal speed across the housing surfaces is not constant.

Survival of a rotary is dependent on 2 main things. The first is bearing life. The engine only has 2 bearings supporting the eccentric shaft front to back. The intermediate housing does not have a bearing for support. At high rpm's this can lead to eccentric shaft flex. That takes us to our second problem.

If the eccentric shaft flexes too much, the rotors can physically come into contact with the side housings, damaging them. Race motors usually run more side clearance to help reduce this risk. Fortunately there is something that can be done which takes care of both issues at the same time.

Add a center bearing. Guru Racing out of New Zealand (I think?) makes custom eccentric shafts and can install a center bearing in the engine. This reduces flex on the eccentric shaft but also adds another bearing which gives you 50% more total area than stock. This one mod alone can do wonders for engine life at higher rpm's, including helping it to make more power.

Why dont Mazda put this in ? Due to cost concerns ?

That would be my guess. The engine already revs as high as they need it to and seems to live just fine. They would also need to make a 2 piece eccentric shaft. If you really want to push the engine hard, it's a great thing to do. Even the 20b lacks a bearing on 1 of the intermediate housings (the thin one).

Taken from the LMP2 thread, I thought this would be a more appropriate thread for this. Ceramicseal replied to the 17:1 comp.ratio in the porsche spyder V8

And unfortunately the rotaries can't take advantage of this same concept. They are practically maxed out in the compression department.

Kinda off topic, I know its stated that rotaries wont gain any more power with increasing compression ratio. Does anyone know the reason behind, or explain it in not too complicated terms?

The results were obtained (obviously) by tests conducted, but that does not state the reason. Also is there any way to fix it? Lets say would direct injection give light to raising the comp.ratio for more power?

I know I've been relating a lot of things to direct injection, however I believe that DI will give a lot more benefit to the rotary engine than we might think. Not just the gains from DI itself, ie, a little better power + emissions, I think it could lead to some major changes in the design of the rotary engine.
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Mazda ran tests way back in the 70's that showed that power remained fairly constant between 9.0:1 and 11.0:1 falling off above and below this point. I have shown earlier in this thread that Mada has raised the compression ratio for emissions, not power reasons. Now as to why more compression doesn't seem to do anything on a rotary. Remember that on a piston engine, the air just gets compressed in one spot. It doesn't go anywhere.In a rotary, we are constantly moving air around the engine. We don't compress it in the same spot that we bring it into the engine or expell it from the engine. The rotor faces have a recessed dish area that determines the compression ratio. The smaller the dish, the higher the compression ratio. The problem with making it smaller is that air has a harder time getting from one side of the engine to the other through this dish as the rotor turns at it's smallest point. When we compress air in a rotary, we do more than just compact it into a smaller space. We also restrict it's flow as it is always moving. It is this restriction that puts pressure on the engine to the point that raising the compression ratio becomes counterproductive to overcoming internal airflow. As a result if we keep raising the compression ratio too much, we'll lose power, even on high octane fuels.

Ah, its perfectly clear now, thanks again RG.

Just one more question... (for today) =D, I hope I am still making positive contribution to the thread, without turning it into my personal Q&A thread.

The question is on the side exhaust configuration in the Renesis. Just power wise, I understand its probably (and truthfully is) limiting power. Comparing the older NA rotary, do you think the side exhaust is any contribution to the power?

Its not the best comparison as the rotary engine + technology + materials advanced a lot in almost 20 years. But what I am thinking is really this.

I want to see it gone, however that'd again introduce overlapping. If the Renesis came with peripheral exhaust, and yes, it wont pass emissions, but we ignore that for now. Do you think the engine would still make the same power? a large decrease or possibly a little gain?

I am imaginating that DI would take care of the emissions, hopefully burn all the fuel in the combustion process. Then we can have peripheral exhaust for optimal flow. Add in a variable length peripheral intake. And only a small side intake for holding idle and low rpm, which can be open/closed.

I think the main problem lies in the huge overlap, and maybe side + peripheral intake is too costly/complex/impractical? and also emissions.. sigh.

I think I am going crazy :Eyecrazy:
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All of the Renesis advancements are a result of the side exhaust configuration. Larger intake ports have some impact on power of course but not nearly as much as many people think it does. While some people will state that the peripheral exhaust ports can flow more than the side exhaust ports, this doesn't really tell us much. While airflow through a port is important, it's timing is also very important. The peripheral exhaust port has too much port timing. More is not always better. If we went back to a peripheral exhaust port in the Renesis we'd drastically lose power. The peripheral port can easily flow the engine's requirements. It can outflow them by a wide margin. The best system is one that flows only what you need it to at the timing that you need out of it. Expanding to what I said earlier, larger is not always better. Sometimes less is better! We have less total flow and less total timing yet we make much more power. That's a real world example if I've ever seen one.

I forgot who asked it or in what thread but someone wanted to know how fast the apex seals travel in relation to the housing surfaces. I found this chart that shows the speed relationship around the engine.

http://www.rotaryeng.net/APEX_SEAL_VELOCITY.JPG

Here's a chart on the inertial loads on the apex seals.

http://www.rotaryeng.net/APEX_SEAL_ACCELLERATION2.JPG

Apex seal temperature.

http://www.rotaryeng.net/APEX_SEAL_TEMP.JPG

That was me, RG.

The first one (rotor speed) is confusing, at least to me. I see the rotor & housing, but can't translate the upper drawing. It appears to be a cutaway of a piston/cylinder at the same power point (max torque) as the rotary, and it looks like the speeds are compared one to the other.

If that's the case, the rotary actually stresses its sliding surfaces more than a piston engine. That surprises me; I'd have thought otherwise.

The rotary clearly has the advantage in inertial loads - it doesn't have that 180 degree change in loads that is so hard on bearings and other parts.

Thanks for the info.

Have you ever come across a chart that shows best fuel economy RPMS at a load? You'd need a vacuum gauge to apply the info accurately to the vehicle's operation, but even knowing the RPM level might help some. I am suddenly attuned to fuel economy since I made a 320 mile round trip to Seattle yesterday and got 10.8MPG cruising at 75MPH in sixth gear. My Dodge Ram Hemi beats that by 5MPG for the same trip at the same speed.

Pilgrim

That's not a picture of a piston. That's a view looking at the rotor from the rotor faces. You are seeing side seal stresses.

Well, I didn't really like the piston interpretation, but it was all I could figure out.

At first glance I thought it was what you said, but now I still don't understand how the velocity figures relate to the drawings, though.

Thanks.

Pilgrim

Dear RG,

I am trying to recall one of your instructive posts that I read long ago. In that post, you were saying (I might not recall correctly) that a rotary engine needs more air flow than a piston engine to get the same power. This does not make much sense to me but there is probably an explanation for it.

I think this thread is the right place to review that topic.

Could you explain how air flow relates in a rotary vs a piston engine?

Thank you very much.

btw is there any possibility that you send me an electronic copy of the SAE papers related to rotary engines? I am very interested in learning about this field since I work in a company that designs and manufactures Diesel and Otto engines for marine and stationay applications (name is GUASCOR). Thank you very much again.

Cheers

jird20

The basic issue with a Rotary engine is that due to the shape of the combustion chamber, the fuel is not used as efficently as it is in a round combustion chamber. It is less thermodynamically efficent than a piston engine, so it needs more air and more fuel to produce the same energy output.

^^ That is it in a nutshell.
The BSFC for a rotary is about 15% higher than a comparable reciprocating piston motor.

Well, MazdaManiac, and Rg as well, you are really well respected sources of rotary culture in Spain, as my good friend Jird20 is ;), please feel free to explain further.

Thanks a lot,

Maikelnait

Bump! dont let the good threads die.
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One of the reason the rotors are cast iron is because it expands slower than the aluminum housing. Major drawback is the weight.

Browsing thru wikipedia.

Thermal expansion for Iron : 11.8 ?m?m?1?K?1
Thermal expansion for Titanium: 8.6 ?m?m?1?K?1
Thermal expansion for Aluminum: 23.1 ?m?m?1?K?1

The units mean they expand how many micrometer in a meter of metal with every degree of temperature increase in Kelvin.

I am just suggesting Titanium because I know it is lightweight metal off my head, however it is not as strong as iron. The melting point is almost the same as aluminum too.

Casting the rotors out of titanium could greatly reduce the weight of the rotors, the cast iron rotors in the renesis weights 9.2lbs each according to Racing Beat. Using the density of Fe and Ti, I think it would be around 4.5lbs for a Ti rotor.

Although the price would dramatically increase, I believe it would still work in race applications. Could possibly reduce the weight by 30-40% of the engine if they use better metals/alloys for the housing, plates, and rotors.

Advantage would be a higher redline, less load on parts, seals, etc.., more reliable.

I am also interested in the harmonics in the engine, I do not have any knowledge in regards to that, I'll admit I learned everything from this forum thru years of reading(join date is last yr, but I been reading since 2003) The rotary engine self-destructs at/near 13k RPM, is there anyway to get around the harmonics so that the max rpm can be raised?

edit: actually Ti is alot harder than Fe.
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I am suddenly attuned to fuel economy since I made a 320 mile round trip to Seattle yesterday and got 10.8MPG cruising at 75MPH in sixth gear. My Dodge Ram Hemi beats that by 5MPG for the same trip at the same speed.

Pilgrim

That is freaking ridiculous fuel economy. There is something seriously wrong with that car.

That is freaking ridiculous fuel economy. There is something seriously wrong with that car.

Yes, you're right. It runs fine, but the mileage sucks - or did. See, things have changed.

What I posted was after two trips to Seattle on Interstates 84 and 90, about 320 miles round-trip, and there is a lot of up, then down on it. The cruise control was set at 75. And the mileage I cited above was pretty damned well-measured and accurate. The runs were made with between 400 and a thousand miles on the car.

Since I posted that I have made two more trips on the same route, cruise control at 80. Mileage has been 18.1 and 18.5.

On a third trip, which built the mileage from 1,100 to 1,500 miles, I took the Interstate over on the previous route, but returned via another one, a two-lane, twisty highway over the mountains (Stephens Pass, for you folks in Washington). No cruise control set on the return, and the return trip was done at an average speed of 65mph, calculating distance into time.
And the gas mileage was 19.3, despite a lot of accelerator use.

What brought about the improvement? I'm not sure, maybe it was sunspot activity. Or a gravity warp. Or ten thousand invisible butterflies pushing me.

I wonder, really, if the computer has some sort of enrichening built into the injection system that operates for the first thousand miles or so. Or something.

All I know is I'm satisfied now.

Pilgrim

what gear were you in for the 10 mpg trip? do you have the gallons filled vs miles at fill up still?

ive gone two ways from portland to wenatchee- up 5 to 90 and then 97 to 2 over to wenatchee and also out east on 84 then north on 97 to 2.

going up and back both ways between 70mph and 80mph(with a ticket just outside of wenatchee at 80-oops) ive had between 21- and 24 mpg for all the legs.

Sixth as long as possible, but I don't let the engine lug. If I can't get decent throttle response with the gear I'm in I drop one or two. I use the cruise cont but I still pay attention to how happy the engines feel.

There are a couple relatively short spots on I-84 and 90 where it calls for fifth, and Blewett pass has a couple short stretches where I use fourth.

I don't keep a fillup log, but I may start if the mileage goes erratic on me. Anything over 16 and I can smile. Eighteen and up and I'm effing ecstatic.

I'm going to call it coincidence, but the improvement took place about the time I began premixing.

Pilgrim

what gear were you in for the 10 mpg trip? do you have the gallons filled vs miles at fill up still?

ive gone two ways from portland to wenatchee- up 5 to everett and then 2 over to wenatchee and also out east on 84 then north on 97.

going up and back both ways between 70mph and 80mph(with a ticket just outside of wenatchee at 80-oops) ive had between 21- and 24 mpg for all the legs.

I am just suggesting Titanium because I know it is lightweight metal off my head, however it is not as strong as iron. The melting point is almost the same as aluminum too.

Casting the rotors out of titanium could greatly reduce the weight of the rotors, the cast iron rotors in the renesis weights 9.2lbs each according to Racing Beat. Using the density of Fe and Ti, I think it would be around 4.5lbs for a Ti rotor.

Although the price would dramatically increase, I believe it would still work in race applications. Could possibly reduce the weight by 30-40% of the engine if they use better metals/alloys for the housing, plates, and rotors.

Ti melting point is vastly higher than Aluminum. That's why they make things like jet turbine blades from Ti alloys.

AFAIK, Ti is a b**** to machine; and there's a lot of machining to a rotor. The price would be incredible. Another problem with Ti is galling. Not sure how that would play out with the apex seals that move in their slots. Certainly you'd need some other metal for the bearing; maybe inserts for the apex slots too. There we go with dissimilar metal expansion again, and perhaps galvanic corrosion. Maybe these problems could be solved but I'm wondering if a set of Ti rotors would cost more than the car?

Don't use bearings! Just create a new rotor and build the bearing in. I know some people say that if a bearing goes out, all you have to do is replace it and put the engine back together. Bearings should never touch each other. That means no oil present. For the most part a bearing failure is uncommon so it's not much of a concern.

does the leading edges on the rotor's need to be blueprinted? Are there any advantages to coating the combustion face on the rotor?
Oldragger

Ti melting point is vastly higher than Aluminum. That's why they make things like jet turbine blades from Ti alloys.

That's not quite correct. They make Turbine compressor blades from Titanium not the turbine blades because like magnesium titanium is combustable. It's good for about 800F. Anything above that and it goes plastic so it would have to be cooled. Also I wouldn't expose it to the combustion chamber. That's how titanium fires get started and if that happens your car burns to the ground from the inside out. :mad:

What about ceramic rotors? they could run at very high temperatures. You'd need to have some kind of metallic fiber reinforcement so they don't crack from shock loads. Or ceramic coating the rotor faces to reduce the rotor metal temps. That may open you up to aluminum or other lighter metals/plastics.

I think everything comes down to cost concerns.

I dont know how the rotors are made, are they machined? or casted from a mold. I know NSX uses titanium connecting rods, so there has been Ti parts used in ICEs. But it seems it might not be a good choice in this application in a rotary engine. Perhaps other alloys. Or just simply aluminum alloys like all other pistons engines. That'd lower the weight down by a lot already.

It seems using light weight materals for the rotors hasnt really been discussed before, there are plenty for the plates between housings. I was just reading the thread about going to 13krpm that guy started.

Biggest concern is E-shaft flex, well I thought maybe we decrease the load on the shaft then we can go higher without making an even stronger shaft. Why go that high?, certainly not in street application, just racing. 9000rpm is enough for a road car.
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What about ceramic rotors? they could run at very high temperatures. You'd need to have some kind of metallic fiber reinforcement so they don't crack from shock loads. Or ceramic coating the rotor faces to reduce the rotor metal temps. That may open you up to aluminum or other lighter metals/plastics.

I am sure some aluminum alloys can stand up to the combustion temperatures of the rotary engine. Maybe its too much chemistry and metallugy here. But the same alloy is used in almost all piston engines now. So I am sure there is a way to make it work.

As for the expansion rates, I think with different use of aluminum alloys would solve it. rotors expand slower, and housing faster.

Did they cermaic coat the 787B? They certainly did for the housing, not too sure about rotors.
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That's not quite correct. They make Turbine compressor blades from Titanium not the turbine blades because like magnesium titanium is combustable. It's good for about 800F. Anything above that and it goes plastic so it would have to be cooled. Also I wouldn't expose it to the combustion chamber. That's how titanium fires get started and if that happens your car burns to the ground from the inside out. :mad:


Titanium's melting point is around 3000 degrees not 800! :crazy:

Nono, Shaunv is right, it combusts with oxygen, not melt. at 800
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I dont know how the rotors are made, are they machined? or casted from a mold.
They are cast. Then the faces, sides, and bearing seats are machined and the seal grooves cut out.

See the Japanese video, they show you Mazda's RE factory (rotary engine workshop) on how they put Renesis together.

Yep, its on my harddrive=d
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See the Japanese video, they show you Mazda's RE factory (rotary engine workshop) on how they put Renesis together.

Where do i find this link? You can buy a GURU 2 piece excentric shaft that weighs around 4.8 kg then you can rew to 13k rpm!

/Lasse

I hope you have an aftermarket clutch plate if you are revving to 13k

Are you writing a term paper or something lol

once again I am ignored. Oh well I will ask my teenage son--he knows everything.
olddragger

does the leading edges on the rotor's need to be blueprinted? Are there any advantages to coating the combustion face on the rotor?
Oldragger
Not quite sure what you mean on the first part. Coating the combustion face would theoretically lower oil temps but make a little better use of wasted heat. The exhaust would be hotter as well.

Are you writing a term paper or something lol
Who me? I wish I could write like that back in school.

Pure titanium will burn just like magnesium, titanium alloys don't. I'm not familiar with what alloys are typically used for the automotive applications though. According to wikipedia: Titanium is used in strong light-weight alloys (most notably with iron and aluminium). So its probably one of those. Interestingly enough though its still 60% heavier than aluminum.

does the leading edges on the rotor's need to be blueprinted? Are there any advantages to coating the combustion face on the rotor?
Oldragger

not to be ignored, this is an interesting question. Are you suggesting that they be ceramic coated? RG would that work?

not to be ignored, this is an interesting question. Are you suggesting that they be ceramic coated? RG would that work?

Maybe Teflon coating? Coating Pistons with teflon is pretty common practice these days to decrease friction and create a surface that carbon will not easily stick too. Nissan uses teflon in several engines including the VQ.

Since the rotor itself does not touch anything (only the seals do), the only benefit I would see from coating it with something would be to reduce carbon buildup. Now coating the seals is a possibility - but I imagine it would be impossible to know if it would be beneficial without a tremendous amount of R&D.

My thoughts on Old Dragger's question:

I would think that if you coat the combustion face with an insulating material like a ceramic you lower the rotor metal temp and you would see less expansion of the metal allowing you to build with tighter tolerances. Most modern gas turbines coat all the hot section gaspath parts with a thin ceramic coating in order to reduce the metal temps so they need less cooling, expand and contract less, and can operate with higher gas temperatures. I'm not familiar with the benefits of higher combustion temps in rotaries. Is there a benfit to being able to turn up the combustion temp?

Turbos.. haha.. but the exhaust gas temp is already so high in rotaries, I am not sure if the consequences would out weight the benefits. Hmm with less heat absorbed I can see a little more power, less energy lost in the form of heat. I dont think the catalysts would like the high exhaust temps...
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Turbos.. haha.. but the exhaust gas temp is already so high in rotaries, I am not sure if the consequences would out weight the benefits. Hmm with less heat absorbed I can see a little more power, less energy lost in the form of heat. I dont think the catalysts would like the high exhaust temps...
Just to give you an idea, I have a custom machined set of exhaust sleeves for a 13B. It holds the exhaust port shape all the way into the header. The stock 13B sleeves expand greatly, doubling their area in about 2" of distance. This slows down the gas speed. The first set of sleeves that were installed were on a turbo 13B. It was a friend's car and he was the one that machined the sleeves for me after I told him what I wanted. He had a large single turbo and the first time he got on it he noticed that the turbo spooled up very fast with the new sleeves installed. Much faster than with the stock sleeves. After only a few minutes though he noticed power fall off and he could no longer make boost. As it turns out, the added heat from the much higher exhaust velocity completely melted the turbine and folded over the blades! This was after only a few minutes. Admittedly that wasn't an inconel exhaust wheel but he ran that turbo for a long time with the stock sleeves in place. Exhaust temps exceeded 2000*F going into the turbo!

Wow! :Eyecrazy: That's pretty cool. Yeah at that temp you need an Inconel turbine wheel and probably some kind of ceramic coating as well. I'm not sure how much heat is lost through a turbo but I could see melting the exhaust too!

Ouch for the turbo..
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Seems the future of the Renesis is in Advanced Materials, alloys, ceramic coatings and seals. Is Mazda willing to spend $$$$ in R&D or will it die?

Just to give you an idea, I have a custom machined set of exhaust sleeves for a 13B. It holds the exhaust port shape all the way into the header. The stock 13B sleeves expand greatly, doubling their area in about 2" of distance. This slows down the gas speed. The first set of sleeves that were installed were on a turbo 13B. It was a friend's car and he was the one that machined the sleeves for me after I told him what I wanted. He had a large single turbo and the first time he got on it he noticed that the turbo spooled up very fast with the new sleeves installed. Much faster than with the stock sleeves. After only a few minutes though he noticed power fall off and he could no longer make boost. As it turns out, the added heat from the much higher exhaust velocity completely melted the turbine and folded over the blades! This was after only a few minutes. Admittedly that wasn't an inconel exhaust wheel but he ran that turbo for a long time with the stock sleeves in place. Exhaust temps exceeded 2000*F going into the turbo!

Interesting, Buick back in the late 80's made a turbo for the Grand National with a ceramic turbine. This sounds like a perfect application for it. I know weight would also be lower which would help with the turbines turbo lag.

Well--thanks--I wasn't ignored.
RG what I meant was the leading edges of the combustion "chamber" on the rotary sometimes (per my research--NO experience with this)are "slightly" off as far as being the same distance from edge of the rotor itself. So in theory each face of the rotory's timing would be just a little off. The Renasis engine may be better build than the older ones and not have this but my reading informs me that on the earier models this was something that was looked at and corrected during modding/rebuilds.
One thing about the combustion chamber coating--it would have to be thing as the clearance is not very big. I agree that it may be interesting to do this.
RG do an old man a favor--I know some are tired of me mentioning the electric water pump--what are your thoughts on that concept--and sorry dont mean to hijack your thread. Just brief. With the Renasis internals/combustion process being so well thought out I just wonder why the peripherals are so ordinary when there is a lot of room for improvment.
olddragger

Ceramic coating of the rotor faces was initially considered for the Renesis, (the initial 184kW/250hp dry sump design) but on further study the coating was found to only be needed inside the new side exhaust ports, then eventually dropped entirely in the production version, along with the dry sump concept.

S

Well I've got some good side by side comparison pictures between the Renesis rotors and the 13B rotors thanks to Jim Langer at Racing Beat letting me play with them. When I get a chance tonight, I'll post them. You can definitely see the side seal differences in terms of size and location. You can also see the apex seal groove depth difference. The interesting thing is that while the side seals are wedge shaped, the grooves are not.

fred- i was thinking about the side seal position change. since the reason for the new shape is for improved carbon scraping, i think the reason for the new placement if the same. having it closer to the edgedoesnt allow as much of a lip for the carbon to bunch up in. also looking at my new 2004 service highlights hard copy- it looks like the groove is narrower at the bottom but the cross section is different than the cross section of the seal

The seals were moved outward to allow a larger intake port. They could push the opening timing even earlier this way without killing the side seals on the closing edge and strangely enough we did seen evidence of contact from this 2 years ago at RB.

well double duty then.

but fred remember why that engine was apart also- because it had blown on the dyno.

Well I've got some good side by side comparison pictures between the Renesis rotors and the 13B rotors thanks to Jim Langer at Racing Beat letting me play with them. When I get a chance tonight, I'll post them. You can definitely see the side seal differences in terms of size and location. You can also see the apex seal groove depth difference. The interesting thing is that while the side seals are wedge shaped, the grooves are not.

Pictures ! We want Pictures !

To the guys that had a chat with speedsource, do you know at what RPM does the Renesis RX-8 shift at? power starts falling at 8500 in the stock engine, is speedsource able to tune it so that it falls off later? I'd be curious to know if they develop 265 hp with the stock power cuve (elevated by quite a lot to give that much more hp) or power keeps building after 9000rpm. Maybe a combination of both. Also any info on the torque number?
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Speedsource is shifting the 3 rotor at 8500 rpm. It's pretty close to that in the 2 rotor as well. Probably somewhere between 8500-9000. As far as I know they didn't raise the powerband on the 2 rotor as they are still using the stock intake manifold and stock porting.

Does anybody know how i shall raise the 8700 rpm limit (according to my RotoTest hub bench) the tach shows 9500 rpm then fuel cut starts? This is very annoying when i dyno my car. Must i buy a Piggyback or is there some quick inexpensive way to do it? If there is not a quick fix what Piggy back shall i buy? Thanks in advice!

/Lasse

You can use an aftermarket ecu such as the Interceptor to change fuel cut. Racing Beat's reflash also raises it. The factory actually has it set at 9000. Your tach is just off. RB raises it to 9300 and the Interceptor raises it as high as you want. The real question is why do you want to do this? Retuning will get your useable rpm limit up a few hundre rpms but for the most part you won't get any more power unless you completely change the intake manifold.

LOL, my OE tach shows almost 10k on the limiter with the RB flash

mine too:)

Charlie, just so you know, I had a hell of a time with security with that engine stand adapter. They made me check it claiming it was heavy and I could really smack someone hard with it. Your airport is where all of the terrorists are getting on!

haha in cali? there's your problem- you didnt have a sign on it:D:

Here you can see the side seal groove thickness differences as well as the side seal location difference. The Renesis side seals are definitely farther out. You can also see the apex seal depth differences.

Very interesting pics...
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DevMichaels cam (http://camslivesexy.com/cam/DevMichaels)

About the rotors pics,

One interesting point here is that the side seals are already max further out (or at least almost max out) in the current rotors so no much future improvement in that area.

In my opinion rotor improvements will have to come from the use of lighter materials. Iron is not exactly a light one and again there is not much room for improvement weight wise. The renesis rotors are said to be 17% lighter than the latest inside the 13b-REW.

Thinking about alternative materials aluminium comes quickly to our mind. However I foresee possible problems with clearances due to a much higher expansion coefficient. Titanium? yes that solves both problems (weight and expansion coeff.) but casting and machining titanium is a nightmare and absolutely expensive.

So who knows what the next generation of rotors will be made of?

Cheers

jird20

What I find interesting is how much of the Renesis' development parallels that of piston engines. For example, moving the side seals closer to the edge of the rotor follows the trend to move the top ring closer to the top of the piston. I guess Mother Nature behaves the same no matter which engine she is in. Could the next gen. rotors be hybrid parts that have lighweight inserts in certain areas?

As far as the metallergy discussion, how about the same technology used in the F20C/F22C engines. The engine is carbon reinforced aluminum. From what I read it decreases the amount of thermal expansion in comparison to many other aluminum alloys, marginally stronger and more durable, light weight, and most important cost effective.

I am just not sure how much of that is good marketing and how much is true. Maybe that technology could be used in the Renesis in the future without increasing costs too much.

Anything lighter is better, I am sure Mazda has experimented with lighter metals/materials for the rotary engine. Hope they'll put it into production when its cost effective.
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RG, as you wrote: " A lighter apex seal can seal better with less spring pressure at higher rpms..."
I thought that a heavier seal needs less spring pressure, because of the bigger forces on it than on a lighter seal.

It depends what the seal is made of. Carbon apex seals are lighter but are softer. They can't use as much spring pressure but seal better above 8000 rpm. Ceramics on the other hand are the lightest out there. They are quite strong though and as such can use a very strong spring. The most important aspect of this is with the natural lubricating ability of ceramics. They are very slippery. Strength and their low coefficient of friction allows them to use high spring pressures. Carbon are soft, weak, and not as slippery. They can't have as much pressure.

I think ceramic rotors would be a better route than Titanium. You don't have to worry about them catching fire, there would be very little thermal growth, and they would be lighter. I'm not an expert, I don't even know what kind of ceramic or where to start but I think the concept could have promise. The problems I see are how to reduce their volunerability to shock and impact such as detonation or the gears on the e-shaft. If you put a metal gear ring inside the rotor then you'll have to deal with the hoop stress caused by the thermal growth of the metal gear ring inside the ceramic rotor.

You could do an aluminum rotor but the casting would have to be much thicker than the current one. You'd also have to modify oil flow through them and oil cooling as aluminum will pick up much more heat. It could be done. I wouldn't go the ceramic route. I don't see how it could survive the stresses.

I have thought about it.. but I dont think its a good idea to have the rotors made of brittle material. Therefore I think light metals/alloys would be the way to go.
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Are we back to steel then? Are the rotors currently cast? If so you could make forged rotors and go lighter. You could probably get fancy with the web of the rotor and make some kind of thin wall type cross section with a good FEA model. That's basically what we did when designing tubine rotors. They would have a thick center and then thin down in the web as you moved towards the rim and then add your combustion and sealing surface.

They are cast. Then the faces, sides, and bearing seats are machined and the seal grooves cut out.

Heres the answer, RG answered a couple pages ago. I think they key is alloys, mixing different types of pure metals will give you benefits you cant find in any pure element.
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I have thought about it.. but I dont think its a good idea to have the rotors made of brittle material. Therefore I think light metals/alloys would be the way to go.

Yeah I agree that's the ceramic problem. Maybe some kind of metal fiber reinforcement. There are ceramic cutting tools for machining metal where they use a "whisker" reinforcement in the ceramic to help keep it from cracking.

no one ever answered my question about the leading edges of the depression. do they need better blueprinting?
OD

er that is ----the depression on the rotor--sorry i wasnt more clear.
od

I don't see why they would need any work. The depressions are all CNC machined so they should match pretty well.

You wrote this RG: "The rounded shape of the seal tip allows gasoline to get under it. As it rotates and tries to compress the air, this added pressure will also be in the gasoline under the seal. This will exert pressure on the apex seal trying to push it into it's groove."

My new question is connecting to my last: If is this "pushing into the groove the apex" is an issue, why is this just at starting the engine?..so if the combustion pressure can push back the apex to its groove (as you said), it has to be an issue when the engine is working, too. What is the difference between when there are gasoline (at cold starting)is under the apex, or oil, or just "air/gasoline mix" with pressure? I hope you understand what I mean.

...and why is enough to use this weaker springs if the lighter apex is pushed by less centripetal force to the trochoid wall (at higher rpms), than the heavier RX-7 apex....and how can we avoid always the compression losting with that weaker apex springs, if it's an issue at starting.

Lower rpm's is where you can have issues. At low rpm's, there isn't much force trying to hold the apex seals outward. Just spring pressure. As the engine rotates faster and faster, you have forces on the apex seal in 2 directions. Towards the housings but also towards the back of the apex seal grooves. Some pressure gets under the seal as well to help hold it outward. There is enough force to easily overcome combustion pressures. Fuel is better distributed and atomized at higher rpms and doesn't ahve te tendency to get under the seals. A cold engine can't atomize fuel easily so it has more of a tendency to pool on the surfaces and this will build up under the apex seals. Combine this with relatively little pressure holding the seals against the housings and it'll flood easier.

further on the leading edges issue--has anyone ever measured them out? Maybe they are off just a tad? Even CNC can be minutely off. IF ----there are some inconsistances, it would be interesting in addressing. In 2 ways. In addressing the exact match of each face of one rotor AND the insuring that the 2nd rotor exactly matches the 1st. The ecu controls each rotor the same-- so if any of the faces dont exactly match in distance from the leading edge then there is room for improvement.
OD

Lower rpm's is where you can have issues. At low rpm's, there isn't much force trying to hold the apex seals outward. Just spring pressure. As the engine rotates faster and faster, you have forces on the apex seal in 2 directions. Towards the housings but also towards the back of the apex seal grooves. Some pressure gets under the seal as well to help hold it outward. There is enough force to easily overcome combustion pressures. Fuel is better distributed and atomized at higher rpms and doesn't ahve te tendency to get under the seals. A cold engine can't atomize fuel easily so it has more of a tendency to pool on the surfaces and this will build up under the apex seals. Combine this with relatively little pressure holding the seals against the housings and it'll flood easier.

Thank's RG. I was confused a little bit, that you call it "under the seal" issue when fuel is in between the apex and the trochoid surface, and when fuel is under the seal in it's groove, in the same time.

I think ceramic rotors would be a better route than Titanium. You don't have to worry about them catching fire, .

Someone better call the NASCAR boys and tell them that their engine valves may catch fire. :mdrmed:

Heat is always being transferred to both the coolant and the oil systems. The temps of the rotors never exceeds about 450*F or so in spots. Titanium has a MUCH higher flash point than that and even Magnesium won't ignite at that level.

600C degrees as per wikipedia.
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I have only measured the 1974-1978 9:2 cr rotors and they were 1-2 mm apart from face to face. Right now i have 12 9:0 cr rotors and i shall when time allows carefully measure the bathtube chambers to apex seal groove.

/Lasse

In my manufacturing experience we've had milling machines burn up dry machining magnesium gear box housings because a chip got too hot, caught fire, and landed in a chip conveyor full of magnesium chips.

When designing jet engines for Pratt & Whitney we didn't use titanium alloys in temps above 800 degrees F and never in the combuster and turbine sections of the engine. I've looked at the remains of test stand engines where the titanium compressor blades got too hot and caught fire. It was nasty and quick.

I don't know what the guys in NASCAR do but I know from my personal experience what not to do with Titanium alloys.

thanks Lasse--if you find some variences then the speculation can begin.
olddragger

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Looks like we need to also call F1, CART, IRL etc etc. :Eyecrazy:

To RotaryGod and others, this is an awesome thread. I'm learning a lot, thanks.

To me the problem with the Renesis is not about its advantages or disadvantages with the 13B. The Renesis is, overall, the superior engine. And it should be, as it came later.

To me, Mazda mistake was not in the engineering, but with common sense and understanding its market. The Renesis is a rotary masterpiece, had Mazda implemented its introduction better or make a few different decisions at key points in its development, it would have simply ruled over everything in it class. As it is, the RX-8 is doing a good job, but it could have done even better.

The problem is that it appears Mazda did not anticipate the need for a higher performance engine that used FI. Mazda should have anticipated this even if the present RX-8 really put out 280 HP to 250 HP at the crank (which it doesn't without mods). This is because their last generation RX-7 turbos were in the 280 HP range and were lighter cars. People would naturally expect improvements over the last RX-7s or demand higher performance relative to the competition. If you know that you are producing an heavier car that can seat 4 people, than you should know that you need more horsepower. If you know that you are not going to meet a certain HP goal with NA, than you should know to prepare to go FI.

The common sense mark would be to introduce a FI version of the Renesis at 300 HP crank. Even if it was going for $5,000 to $7,500 more, it would have been a hit. Mazda could have simply adjusted production numbers of the FI Renesis and the NA Renesis based on customer demand. Why would Mazda not do something that seems so logical?

Also coming out with a 4 port and 6 port engine, seemed a bit of a waste to me. By having just a 6 port engine, you have a STANDARD engine. You are making most things in the Auto and MT interchangeable and reducing cost and decreasing performance variances.

Just to have produced a 4 port and to de-tune it, was a bit nutty to me. Think about all that wasted effort and energy. Why go out of your way to DE-TUNE an engine and go cheap on parts (no 2nd oil cooler, inadequate ATF cooler, etc...)? A standard 6 port engine, at the very beginning, would allow you to focus more energy on FI development of that engine and save money.

It would have been better for Mazda techs to have figured out the FI issue, during the R&D phase of the Renesis. This says to me, that perhaps the ultimate HP numbers of the renesis were overestimated long before emissions became an issue on the production models. Maybe Mazda techs though they could hit 280 HP or above, but a combination of issue caught up to them and prevented the Renesis from seeing those number in it NA form. This could also explain why nobody brought up the issue of going FI earlier, since they may have thought that the NA Renesis would put out higher HP numbers. Yes, the NA Renesis puts out higher numbers than an NA 13B, put you need to factor in weight and competing cars in its class. Again, making it obvious that if the NA Renesis did not hit a target HP that you should consider FI and think about that during R&D or during the early production phase.

Also, the Mazda ECU appears odd to me for a couple of reasons. It was if they never anticipated going for higher performance gains and an aftermarket. The ECU seemed to become important when it came to emissions, and a "hack" was thought of. A lot could have been done by having an easy to tune and program ECU. Eventually, people will crack the ECU and make better flashes, but it will be Pro-Tuners and not Mazda Techs. Same goes for FI, it will be Pro-Tuners that get the Renesis to really soar and not Mazda or Mazdaspeed. That is outrageous, when you think about it.

After reading about the horsepower speedsource cars make, I think the next generation Renesis will be able to make 280-300HP crank in NA form. Some of the things discussed in this thread arent that hard for Mazda to put into production. Direct Injection (better emissions, more power), lighter housings (lower weight), *possibly* lighter rotors (more power, higher rpm), also rework the exhaust ports to flow better (more horsepower everywhere, especially high rpm).

DI will definatly make it into an rotary engine. I am sure of it.

Put this motor in a 2 seater, it'll do low to mid-5s 0-60 consistently.
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I agree with a non turbo, lighter material and DI future. Aluminum house and rotors, not sure about the Eshaft.

direct injection question:
in the mazda disi engine the fuel psi is at or around 1600, would this be a suitable psi for a DI rotary??

also would the combustion face have to be redesigned in order to flow the vapor over the spark plugs in a more controlled manner or would it be control via injector placement?

Its more like 400-1600psi.

Haha, you'd have to ask RG for those =d
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NikkiBender live (http://camslivesexy.com/cam/NikkiBender)

The DISI engine runs 1800 psi of fuel pressure. I nkow the person who is wokring on DI with Mazda and he's here in the U.S. Unfortunately he won't tell me much as it's not his info to pass along but he did say the biggest challenge right now is getting the fuel pressure he wants. Remember the RX-8 runs somewhere between 38-43 psi of fuel pressure. I don't remember exactly but it's not far off. The DISI engine runs 1800 psi. He wants over 20,000 psi of fuel pressure!!! That's new common rail diesel pressures. The problem is with getting that pressure.

Logic would say to use a diesel style pump. This won't work. Those pumps are mechanical and are lubed by the fuel going through them. Diesel fuel is an oil. It lubricates. Gasoline doesn't. We'd burn up pumps. We also can't just make a pump that is lubed off of engine oil as the pressure differetial on the pump seals would be nearly 20,000 psi. The seals would fail immediately. That's the biggest thing holding it back.

They can make DI work on a rotary now but it is limited in it's abilities and not really worth putting into production at this time. They are working on it though. An interesting tidbit is that fuel injector location has a huge effect on fuel pressures required to do the job properly. Think about that one for a while.

Maybe the rotary should make the switch to diesel!! its fast burning too!. Spark ignited diesel rotary.
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Avandia Lawsuit (http://www.classactionsettlements.org/lawsuit/avandia/)

Diesel burns slower. Saying that, I don't object to the idea of a diesel rotary.

earlier experiments on DI rotary's were done with low pressure fuel injectors and were found to be sucessful at some levels. The ultra high pressure idea is needed if your going to inject the fuel right into the chamber between the spark plugs.

I'm still collecting the SAE papers on the subject.

What are the advantages of injecting fuel during compression or ignition?

Edit: Brillo answered my two previous questions.

i believe the injector location for a tradition piston DI engine is directly above to slightly more intake valve side. I think they mainly created a looping path for the fuel that turns toward the spark plug during compression to make timing easier (a quick MSpaint of what i'm thinking):http://i96.photobucket.com/albums/l187/dillsrotary/DI.jpg

I might be wrong, i'm not to trained in internal combustion, just going off some personal thought and learned physics. But to adapt DI to the rotary i was curious to the injector pressure because of the curved path of the rotor in compression towards ignition. A piston engine is 1 dimensional towards compression while a rotor is moving in 2 dimensions so i cannot think of a predictable path of injected fuel. Maybe thats while your friend wants 20K psi for instant atomized liquid fuel to a gas, which seems to erase the problem i'm thinking of in my head.

oh man, sorry, thanks for the correction, i dunno why i said diesel is fast burning, if it does it wouldnt have such a low rpm!.. my bad=/
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Another question: Could you step up the pressures though as series of pumps? You could have a lower pressure high flow pump in the gas tank and then two smaller pumps to step up the pressure in the engine compartment. One for each rotor (variable fuel pressure for each rotor) so you wouldn't have 20K PSI fuel running the length of the car and reduce your seal pressure differentials.

That is indeed what the MS6 has. a low pressure pump and then its bumped up to 1800psi with a high pressure pump in the engine compartment, i think its right above the engine from what i learned.
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Oh. Well let me tell you about this wheel thingy I just invented... :)

There are many things to consider when it comes to injector placement in a rotary. In a piston engine, you are pretty limited on where to put it. It's going to be in the vicinity of the spark plug. On a rotary, the injectors can be near the intake port way across from the apsrk plugs, right at them, or anywhere in between. The closer you get them to the spark plugs, the higher the chamber pressures get due to compression. This means you need more fuel pressure to atomize properly the closer to the plugs you get. As you move the injector towards that side of the engine, you also have less time to inject the fuel. Once you get this figured out, you still need to work out what direction the injector is sprayed as well as rotor dish shapes and fuel spray timing needed in order to get the most efficient use of the fuel injected. There's alot to worry about and much of it is far more complex than DI in a piston engine.

Hmm.. I think the rotary would need the injectors to be near the spark plugs, in the combustion chamber to make the most benefits. That'd lower the surface the fuel will stick to. To help with emissions and gas mileage. Those are the number one things the rotary needs right now. Maybe that is why the Mazda engineerer wants the 20,000psi of pressure so bad.

The MS6 gets quite good mileage last I checked (especially during crusing, when the motor can run in super lean burn), and its turbo-ed. I think direct injection in a NA engine will get very very good gas mileage. Very lean burning could be achieved.
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Your intake charge temperature is also a lot higher. How would that change your atomization effectiveness and mixing?

High fuel pressures through very small injector orifices and proper aim and timing of fuel injection takes care of that problem.

Would you want to move away from a primary and secondary injector setup and more towards a parallel injector setup at different orientations or locations to get more coverage of the charge since your injecting fuel later in the cycle and have less time to mix?

It would seem that for di a differant combusion shaped depression could be used? .blows my mind just trying to grasp the concept/advantages. Maybe two combustion chambers to each face? Am i Crazy?
Olddragger

I dont know about that, but there is so much unknown to us. It really isnt as simple as piston engines. It seems to me that developing the DI rotary would need a lot of R&D budget too... There are many things to change and combinations to experiment with.
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Would you want to move away from a primary and secondary injector setup and more towards a parallel injector setup at different orientations or locations to get more coverage of the charge since your injecting fuel later in the cycle and have less time to mix?
The DISI engine as far as I know does still run conventional injectors as well. At low rpms it runs only on the direct injection. As rpms rise it hands off to conventionlly located injectors. Keep in mind since I haven't seen one of theose engines up close, I'm only going by what an owner (MS6) friend of mine told me. Maybe Paul from Mazmart can fill us in on this one.

Speedsource Racing also alters which injectors get used on their 3 rotor race car except it isn't direct injected. The primaries are located right at the base of the manifold pointing directly into the intake port. As rpms rise, an additional set come online up by the throttleplates. They slowly handoff from the primaries to the secondaries. This supposedly increases fuel mixing.

DI has some of these things to work out and one way to do it is to raise fuel pressures up real high.

It would seem that for di a differant combusion shaped depression could be used? .blows my mind just trying to grasp the concept/advantages. Maybe two combustion chambers to each face? Am i Crazy?
Olddragger

With older experiments, Mazda has altered the shape and location of the rotor dish. They've tried precombustion chambers and different injector locations. They've been working on DI in the rotary engine for at least 15 years now and are still working on it. There is far more to worry about in the rotary due to combustion chamber shape than there is by applying DI to a piston engine.

Hmm RG, I think the DISI only has direct injection injectors. The Lexus IS has both convention and direct injection. The Speed6 guys are discussing if they need to add convention injectors in the manifold once they reach the limit of the injectors, since they wont be able to find any aftermarket solutions for higher flow direct injection injectors.
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Could be. As I said, I don't have any personal experience or knowledge about that engine.

RP what do you think about mikronite process on the housings.(they just bought out crane cams)--hearing good things.
olddragger

rg,

comments on this thread. i think it will interest you...

http://www.rx8club.com/showthread.php?p=1611752&posted=1#post1611752

beers :beer:

I'll get to it when I have a chance. I will say that raising the compression ratio won't do anything for power.

ok now just out of curiousity ive gone to school to work on cars........however have limited information on the rotary.........ok someone had posted in earlier posts......reguarding the rotors and the dish area on them that has to do with compression ratio......since our rotorsr so much better in effect as apose to u know the older 13b rotors......would it not make since for someone to take our same design n in effect make a bigger dish area to compensate for those wanting to go FI......have good strong rotors yet also having a decrease in compression for an increase in boost. Or is there someone out there with the skills, to say if u had the cash buy an extra set of renesis rotors, n have someone use there talents n create a bigger dish area........???? just my thoughts dont wanna get flamed but i my self am goin FI soon......n if i could run a little extra boost it would be nice........especially considerin my car drinks crappy 91 CA gas.....but its V power as apose to ARCO lol if anyone can message me on what i just said n let me know ur thoughts on it........i would appreciate it.

There are many with the skills to lower the compression on the Renesis, but there isnt a market to buy them.
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Hello everyone!

I’m bringing back this old thread because I think it’s a real shame that such an amount of great technical information gets lost.

A little more than one year ago, here, there were speculations about possible performance increases of the current renesis, as well as an interesting discussion about direct injection for the rotary. I think that the creation of the 16x could be an interesting point to start this discussion once again.



On top of that, I’d like to add a couple of things that had been floating in my mind:

First of all, I’ve been thinking about the feasibility of a hybrid intake and exhaust system for the rotary. As we know, side ports are very good at precisely controlling the airflow of gases going in and out of the engine at lower speeds, whereas peripherial ports allow an engine to reach very high peak power numbers. So the idea would be this, have an engine with both side and peripherial ports, with butterfly valves used to select only the most effective gas paths for every condition.

I think that such a thing was attempted several years ago by Mazda for a competition 10A engine (a butterfly valve was used to select between a side and a peripherial intake port), but no road engine ever did this as far as I know.

Going on with this reasoning, I don’t see great problems in doing the intake the way I described.
The real problems come from the exhaust, particularly when it comes to creating a valve able to stand the heat of the exhaust stream. And on top of this, this valve would also run the risk of being clogged by carbon deposits.
For this second problem, I thought that the valve could be operated whenever possible, so that it would “sweep” its seat free of carbon: during deceleration this valve could be cycled several times and, for example, every few minutes of low load operation the valve would be quickly opened and closed, causing only a minimal power loss and providing the already mentioned sweeping action.
The more I think about it, the more I feel it’s a feasible and good idea. If someone can think a reason other than cost or marketing constraints that forbade this solution from being adopted in a production car, I’d be curious to know.


The second point is more radical. It is all based on a single question: must the apex seals be straight?

To understand what I mean, take a look at the (very crude :) ) rendering I did of a standard rotor (the one to the right, without the red pieces) versus one with curved apex seals (the one with the red pieces). You should see what I mean with “curved” vs. “straight” apex seal.
So, after the “what” section, you’d expect the “why” section; however, before that, I have to go to the “how” section.

As some may already have imagined, such curved apex seals would not work with a standard housing. They would need a new, grooved, housing.
The fact is that, since the angle at which the apex seals are with respect of the housing surface does vary, the groove on the housing cannot have the same depth everywhere. It’ll have to be deepest where the seals are perpendicular to the housing surface and flatter elsewhere.

And here comes the “why”: the housing groove would have to be deepest, among other places, right where the minor axis of the throchoid is, that is between the spark plugs. In other words, it would form a channel for the gases to pass, while in the current design the gases are forced to pass this “chokepoint” using the rotor recess. And, in turn, this is why increasing the compression ratio with a straight apex design (that means making the recess smaller) beyond 9:1 does not bring appreciably more power.
On the other hand, the housing groove on a curved apex design would provide the same passage area while allowing higher compression ratios.
In fact the deepest groove area between the spark plugs is surrounded by the shallowest groove areas immediately above and below it. This means that at TDC the chamber volume will still be small.
Conversely, the BDC positions will use housing areas with deep grooves (the areas near the major axis of the throchoid), thus increasing chamber volume.

Also, the more rounded shape of the combustion chamber might help with the heat loss problem.

Just like with the eccentricity of the housing, it will be possible to choose how much curved the apex seals will be, going from a nearly straight design to a heavily curved one. Of course the optimal bend radius would be determined after several experiments.

I know, it’s a very radical modification, but, at least to me, it seems it would be effective. Does anyone know if such a thing was ever attempted before?

Opinions?

P.S.: I hope that what I wrote was understandable :) . Writing such things in a language that is not your own is not that easy!

On top of that, I’d like to add a couple of things that had been floating in my mind:

First of all, I’ve been thinking about the feasibility of a hybrid intake and exhaust system for the rotary. As we know, side ports are very good at precisely controlling the airflow of gases going in and out of the engine at lower speeds, whereas peripherial ports allow an engine to reach very high peak power numbers. So the idea would be this, have an engine with both side and peripherial ports, with butterfly valves used to select only the most effective gas paths for every condition.

I think that such a thing was attempted several years ago by Mazda for a competition 10A engine (a butterfly valve was used to select between a side and a peripherial intake port), but no road engine ever did this as far as I know.

Going on with this reasoning, I don’t see great problems in doing the intake the way I described.
The real problems come from the exhaust, particularly when it comes to creating a valve able to stand the heat of the exhaust stream. And on top of this, this valve would also run the risk of being clogged by carbon deposits.
For this second problem, I thought that the valve could be operated whenever possible, so that it would “sweep” its seat free of carbon: during deceleration this valve could be cycled several times and, for example, every few minutes of low load operation the valve would be quickly opened and closed, causing only a minimal power loss and providing the already mentioned sweeping action.
The more I think about it, the more I feel it’s a feasible and good idea. If someone can think a reason other than cost or marketing constraints that forbade this solution from being adopted in a production car, I’d be curious to know.



It's the maiden post so let me just say this is a great site and I enjoy referencing the vast knowledge here.

As to your hybrid exhaust ports, I would think that in addition to the carbon deposits that would surely build up on the inside of the unused port, there would also be an added level of aerodynamic inefficiency added to the chamber as it came past this lip. That'd create turbulence and probably reduce the amount of exhaust evacuated.

I was thinking along your lines, how about if you could create a hybrid port using both port types at once, 1 Peripheral connect through the housing to 1 Side Port. Rotarygod talked about the sudden pulses of the peripheral exhaust port... behind each one of these strong exhaust wave pulses there is a low pressure area (sort of like the big trough behind a large wave). If you made a peripheral port that had a smaller size than a 13B (so as to not suck out too much of the gasses in the initial burst), you could create a pulse down the pipe and connect the port to a side port immediately after the peripheral port. That way the power of the pulse from the initial peripheral blast could suck out the gases through the side port, or at least help to, especially as the rotor passes the peripheral port but the side port would still be exposed. The gasses of the side port would help fill in the pressure drop behind the peripheral wave, and allow the burn of the air/fuel more time to complete.



The second point is more radical. It is all based on a single question: must the apex seals be straight?

To understand what I mean, take a look at the (very crude :) ) rendering I did of a standard rotor (the one to the right, without the red pieces) versus one with curved apex seals (the one with the red pieces). You should see what I mean with “curved” vs. “straight” apex seal.
So, after the “what” section, you’d expect the “why” section; however, before that, I have to go to the “how” section.

As some may already have imagined, such curved apex seals would not work with a standard housing. They would need a new, grooved, housing.
The fact is that, since the angle at which the apex seals are with respect of the housing surface does vary, the groove on the housing cannot have the same depth everywhere. It’ll have to be deepest where the seals are perpendicular to the housing surface and flatter elsewhere.

And here comes the “why”: the housing groove would have to be deepest, among other places, right where the minor axis of the throchoid is, that is between the spark plugs. In other words, it would form a channel for the gases to pass, while in the current design the gases are forced to pass this “chokepoint” using the rotor recess. And, in turn, this is why increasing the compression ratio with a straight apex design (that means making the recess smaller) beyond 9:1 does not bring appreciably more power.
On the other hand, the housing groove on a curved apex design would provide the same passage area while allowing higher compression ratios.
In fact the deepest groove area between the spark plugs is surrounded by the shallowest groove areas immediately above and below it. This means that at TDC the chamber volume will still be small.
Conversely, the BDC positions will use housing areas with deep grooves (the areas near the major axis of the throchoid), thus increasing chamber volume.

Also, the more rounded shape of the combustion chamber might help with the heat loss problem.

Just like with the eccentricity of the housing, it will be possible to choose how much curved the apex seals will be, going from a nearly straight design to a heavily curved one. Of course the optimal bend radius would be determined after several experiments.

I know, it’s a very radical modification, but, at least to me, it seems it would be effective. Does anyone know if such a thing was ever attempted before?

Opinions?


As to this second point, I would think the answer is relatively simple, but like I said it's my first post so I'm not a rotary god by any means.

Centrifugal force acts on the air/fuel as it is rotated in the housing. With a flat apex seal, as the air/fuel is pressed against the housing evenly across the width of the rotor. Creating an even pancake. With a curved housing I imagine the combustion would probably be slowed. The fuel would probably sink into the trough, not atomizing as fully as the flat shape.

Also I'd imagine the tolerances would have to be tighter because of the seal extending out into housing, and they'd be further from the axis of the eccentric shaft and amplify the flexes of the shaft at high rpm.

Lastly, the curve would make the apex seals longer increasing the amount of friction.

Please feel free to correct any mistakes in understanding I might have about rotary function. I'm on my first rotary engine and enjoy it thoroughly, though I'm pretty revved up about getting a 16x when they hit the states (as long as it's not mounted in a CX-7 or something)

The topic of heat keeps coming up in here. Especially in relation to the exhaust and the catalytic converter.

I was thinking, what if mazda created an upper exhaust manifold that included a water jacket. This way, the combustion temperatures could be raised through either more radical ignition or compression (a la fmzambon) and still be cooled to the point of equalling an Otto cycle at the catalytic converter.

The manifold would only need to be like 8" out of the ports and could bolt up with a metal gasket. Then from there, a more traditional tube unit could carry it down to the cat. Also, since the exhaust would be undergoing rapid cooling and slowing, the pipe diameter would have to be kept small to maintain exhaust velocity to an adequate level.

The water from the manifold would probably need to be run through it's own heat exchanger at the front of the vehicle before being re-introduced into the cooling system.

However with this exhaust cooling system, I imagine that under hood temperatures would drop sharply. The cat would have more life and performance could be raised while still meeting emissions controls.

The topic of heat keeps coming up in here. Especially in relation to the exhaust and the catalytic converter.

I was thinking, what if mazda created an upper exhaust manifold that included a water jacket. This way, the combustion temperatures could be raised through either more radical ignition or compression (a la fmzambon) and still be cooled to the point of equalling an Otto cycle at the catalytic converter.

The manifold would only need to be like 8" out of the ports and could bolt up with a metal gasket. Then from there, a more traditional tube unit could carry it down to the cat. Also, since the exhaust would be undergoing rapid cooling and slowing, the pipe diameter would have to be kept small to maintain exhaust velocity to an adequate level.

The water from the manifold would probably need to be run through it's own heat exchanger at the front of the vehicle before being re-introduced into the cooling system.

However with this exhaust cooling system, I imagine that under hood temperatures would drop sharply. The cat would have more life and performance could be raised while still meeting emissions controls.


This could be an interesting idea, provided one has enough cooling capacity available. This is the real problem IMHO, getting enough cooling capacity.
After all, even in the current renesis, the exhaust runners are surrounded by water passages, so a simplified version of your idea is already in action.

Furthermore, the warmup phase could not be altered: a secondary water pump (or even a simple thermostat) could be used for the exhaust cooling circuit, and this pump could only be switched on after the catalyst has reached operating temperature.

By the way, as far as I understand it, a higher compression ratio would result in a naturally lower exhaust gas temperature, due to the greater amount of heat that's converted into useful work during the expansion phase overwhelming the higher initial combustion temperature. But I may be wrong on this point :)

Just one more thought about my curved apex idea and your point about the fuel concentrating in the trough: couldn't this concentration be used to create a stratified charge engine? I mean, the spark plugs are palced along the middle of the groove, exactly where the fuel tends to concentrate. This sould mean that even a low amount of injected fuel would produce a mixture around the spark plugs that's rich enough for ignition. Better fuel consumption is my next thought...

Just one more thought about my curved apex idea and your point about the fuel concentrating in the trough: couldn't this concentration be used to create a stratified charge engine? I mean, the spark plugs are palced along the middle of the groove, exactly where the fuel tends to concentrate. This sould mean that even a low amount of injected fuel would produce a mixture around the spark plugs that's rich enough for ignition. Better fuel consumption is my next thought...
Hmmm, ok I think I've got an analogy that might help with this. Let's say you had 500 people that all needed to eat a 3 course meal in 5 minutes. Now, you have two ways of timing this 5 minutes. You could have them all sat down at different tables, homogenously spread throughout the room with their food all put on plates in front of them. Or you could have the tables and the food already out there, but all of the people standing jammed to one side of the room. When you start the timer, the people sitting are going to have alot more time to eat than the people standing.

This is like the gas particles (people) and the food (air). Without being in the midst of the air, the fuel won't combust. This is why you hear them going on about fuel atomization (making the finest mist possible) all the time in relation to fuel economy. That's why GDI with the piezo injectors are such a big deal because fuel pressure goes up from the low 100 psi range (120 psi was about the limit) to anywhere from 200 (as seen in the 3.0L BMW twin turbo N52 motor) to 4000 psi in an injector that is 5 times as fast as a standard fuel injector. Plus by putting the injector directly into the combustion chamber, you can run a wider angle spray than in the inlet, making the air/fuel mixture homogenous across the entire rotor. Also, by injecting fuel straight into the chamber at the start of compression, you give the fuel less time to heat up, thereby increasing lowering charge temperatures before ignition. Lower charge temperatures means more compression can be achieved without risk of detonation, more compression means faster flame fronts and more complete combustion before reaching the exhaust ports. Better fuel economy for everyone.

Does that help? :)

I understand what you mean, but I was looking at this situation the other way round. That is, if there is very little total fuel in the mixture, then this concentration could be useful, instead of a problem.

If this amount of fuel were evenly distributed in the whole chamber, the resulting mixture would be way too lean to be ignited (reliably) by a spark plug.
This concentration would make the mixture (locally) rich enough for ignition. That's what I meant, if it makes any sense at all :)

Ohhhh, I got you.

Why would you pump all that extra air into the engine if you weren't going to use it? Also, this would cause it to run super lean and possibly burn the sparkplugs. At least if you allowed the fuel to fatten up when you hit the gas pedal because your ignition wouldn't be able to do both well without changing physical parts. It seems like it'd be easier to try that cylinder shutdown thing that they have now for the pistons. Just have the computer not inject for said rotor or produce spark on it's pass. Balance this with the other rotor so the eccentric shaft doesn't go all wobbly.

That super lean mode would be useful for idle and very low load operation. It's basically one of the ways in which direct injection reduces fuel consumption (ultra lean operation at low loads).
The spark plugs would be in the fuel rich area, so I don't see a great problem with them getting damaged.

The problem, as you say, is the piggy rich mixture with a normal injection volume. But that can be avoided if the fuel is injecter directly into the engine just before the spark plugs. This way, it does not have the time to collect in one spot and will remain well distributed. This solution would call for (at least) two injectors per rotor, but the new 16x appears to already have this number of fuel injectors (the only difference is that, with the 16x, one is in the intake manifold); the only problem remaining is getting enough fuel pressure to be able to fire a fuel injection right at the highest pressure position in the engine (near the spark plugs).

Rotor deactivation would be another thing to consider. Just disable the fuel injectors for one rotor (the ignition system can remain active or be switched off, it doesn't matter) for a certain amount of time. After that, reactivate the rotor and, when it's running steadily, deactivate the other rotor. This way both rotors get their "rest" time and their "working" time, and wear should be well balanced.
Then, if during single rotor operation you press the gas pedal a little more, the inactive rotor comes back on line and the engine is immediately able to provide full power.

Leave it to us Italians to come up with the craziest, most complex engine possible *cough*Desmodromic*cough* :lol:

Naaahhhh...

I prefer rotaries :)

Both simpler and more complex than a desmodromic engine at the same time...

Rotaries are quite fascinating, though I wish another company would take a swing at making one. Mazda is a good company, but it seems like more expensive production methods of some componentry in the engine would not hurt profit margins and would make these engines go faster and longer.

We all agree that piston engines have thousands more moving parts than rotaries and are alot bigger (more metal). Motors like the 3.5L V-6 out of the TL Type-S (J35A3) and the 3.0L Twin Turbo BMW (N52B30) are loaded out with sweet magnesium components and variable timing systems. You can get both of these engines in cars that are less than $10000 US dollars more than a 40th edition RX-8. My question is, what's holding Mazda back from spending more on material and production costs for an engine that's half the size of most Otto cycle engines?

Simple answer: low production volumes.

Were the rotary used by more models, development costs could be spread much more. High development costs for a low volume item mean much higher final price; thus lower sales.

If you can't increase production volumes, the only other alternative is to limit development costs. Otherwise you need to get something serious to sell for that price (think Nissan GT-R, BMW M3 and up toward Ferrari, Lamborghini and the like).

Simple answer: low production volumes.

Were the rotary used by more models, development costs could be spread much more. High development costs for a low volume item mean much higher final price; thus lower sales.

If you can't increase production volumes, the only other alternative is to limit development costs. Otherwise you need to get something serious to sell for that price (think Nissan GT-R, BMW M3 and up toward Ferrari, Lamborghini and the like).
I was just saying that all of the housings are probably about 1/2 the volume of metal that a standard V-6 engine would use for head and blocks. That trend continues throughout the drivetrain.

I suppose you're right though. Maybe they could just offer two engines like most car companies do it. Make 90%-95% the standard rotary and make a limited run super trick motor with the magnesium parts, engine coatings, billet eccentric shaft, ceramic apex seals, Moly coated side seals. I'd pay for a $40000-$45000 RX equipped out like that for sure.

it's threads like these that keep me loving this site..

Just wait until the book comes out! ;)

Bump this one.

The RX8 has three fuel injectors and two fuel rails. The Secondaries fire in the intake manifold which has been shown to improve mixing of the air/fuel and more complete atomization at high loads (in addition to cooling benefits) in piston motors. The downside being that in low load situations the fuel can actually create an intake backfire (in extreme examples on piston race motors; sudden deceleration has lit air boxes on fire).

The primaries fire much closer to the ignition event (P1's are more responsible for low load and idle; then the Secondaries come on in order to provide better fueling in the torque peak; and then the P2's come on in order to (and here is my question):

1 - Cover fueling shortfall by the P1,Secondary combo (despite its less stellar location).

2 - Cover fueling shortfall and needs less time to fully atomize at the super high load point of the engine.

I am curious as to how the physical location and the stock fueling maps are interrelated.

Caveat - I may 100% wrong in which case I anxiously await correction.

On a related note; it looks as though the stock PCM is set to push all the fuel on the P1; and then once the Secondary come online; then it ramps them equal; and at high RPM it actually gives the Secondary more fueling than the P1.

So it would seem that the PCM has a small preference toward the Secondary; but doesn't actually push more fuel onto that injector - even though it could.

Thoughts?

They *probably* have their reason to do what you said above, but I still think Mazda is having a hard time trying to perfect the timing of the engine.

What we're seeing is probably the *closest* to perfection.

The newest flash actually advanced the timing a bit isnt it ?

Yeah timing is a whole nother ball of wax - I am just trying to understand what they are doing fuel wise; but it appears that they are kinda working something like this.

http://www.usrallyteam.com/content/tech/injector_staging_article.pdf

Yeah timing is a whole nother ball of wax - I am just trying to understand what they are doing fuel wise; but it appears that they are kinda working something like this.

http://www.usrallyteam.com/content/tech/injector_staging_article.pdf

they mention Cosworth in the article, hmm, too bad they dont do any Rotary stuff :(

I like their MZR parts ... :)

LOL - FOCUS MAN!

JK, it would be nice to have a lot more smart people on all of this; but every bit we learn helps. I have a plan to emulate Mazda's stuff as close as possible; I'll uplod it soon.

LOL - FOCUS MAN!

JK, it would be nice to have a lot more smart people on all of this; but every bit we learn helps. I have a plan to emulate Mazda's stuff as close as possible; I'll uplod it soon.

Well, who knows what Mazda is thinking. After all this is their engine, and they've been working 40 years on it. Maybe they're working on something like that. Who knows :)

it seems that with every flash they just *feel like* to try something new.

Well, who knows what Mazda is thinking. After all this is their engine, and they've been working 40 years on it. Maybe they're working on something like that. Who knows :)

it seems that with every flash they just *feel like* to try something new.

HAHA; you may be right - we are beta testing. I am in the Army; so Im used to it.

Guinea Pigs FTW!

HAHA; you may be right - we are beta testing. I am in the Army; so Im used to it.

Guinea Pigs FTW!

I hate to say it but ... yeah I think we're all Guinea Pigs ...

I am still on Last recall's flash(RB version) and I premix so Im ok for now ... I kinda want to do MSP16 cuz people's result are pretty positive.

thinking ...

Too bad there isn't an easy way of changing out just the 6th gear ratio. All the other ratios are fine with me, but 6th is too short.

I 100% agree. I don't even care for the jump between 5th and 6th. All the other upshifts pretty much drop my revs exactly where I want, except for 6th. I'm all for close ratios; but why does 5-6 have to be even closer than 1-2, 2-3, 3-4, or 4-5?

:banghead:

That super lean mode would be useful for idle and very low load operation. It's basically one of the ways in which direct injection reduces fuel consumption (ultra lean operation at low loads).
The spark plugs would be in the fuel rich area, so I don't see a great problem with them getting damaged.

The problem, as you say, is the piggy rich mixture with a normal injection volume. But that can be avoided if the fuel is injecter directly into the engine just before the spark plugs. This way, it does not have the time to collect in one spot and will remain well distributed. This solution would call for (at least) two injectors per rotor, but the new 16x appears to already have this number of fuel injectors (the only difference is that, with the 16x, one is in the intake manifold); the only problem remaining is getting enough fuel pressure to be able to fire a fuel injection right at the highest pressure position in the engine (near the spark plugs).

Rotor deactivation would be another thing to consider. Just disable the fuel injectors for one rotor (the ignition system can remain active or be switched off, it doesn't matter) for a certain amount of time. After that, reactivate the rotor and, when it's running steadily, deactivate the other rotor. This way both rotors get their "rest" time and their "working" time, and wear should be well balanced.
Then, if during single rotor operation you press the gas pedal a little more, the inactive rotor comes back on line and the engine is immediately able to provide full power.

I'd love to see rotor deactivation as you described, along with a stop-start system in the 16X. If Mazda included both of those features, that might actually be compelling enough for me to consider trading my 2004 RX-8.