Let's all have a discussion of the cool engine that will power the Rx-8! Hopefully, I understand some of the charactersitics of the new engine well enough to intelligently discuss them. If i don't, I hope that this discussion will educate me.

The renesis works much like other internal combustion engines by igniting an air-fuel mixture and using the expansion to do mechanical work. How can engines make more power?

1. More displacement - Is there no replacement?

2. Better volumetric efficiency - How much air can we get in the engine?
a. Stuff more air into the engine (ie. turbocharging, supercharging, Nitrous, Miller cycle?) More air is good. Compressing air also heats it though.
b. Cool the incoming air (ie. intercoolers, nitrous) Cool air is good because it is more dense.
c. Let more air into the engine. (ie. dual intake valves, tuned intake manifolds) More air is good.
d. Let exhaust leave the engine easier - (ie. dual exhaust valves, headers, high flow exhaust) More bad air going out means more good air can come in. More air is good.

3. Better use of the air/fuel mixture for power (Thermal efficiency)
a. Higher compression ratios. The air-fuel mix will be more prone to detonation & will need higher octane gas though.
b. Better thermal efficiency
c. Improved fuel atomization
d. More powerful spark
e. Better combustion stability

4. Less friction / resistance to movement (Mechanical efficiency)
a. Use lighter weight moving parts - waste less energy
b. Improve pumping losses (ie. Miller cycle with shorter compression stroke than expansion *huh?*)

How and why does a renesis make more power than previous rotaries?

1. Larger displacement - No.

2. Better volumetric efficiency
a. The side exhaust allows an intake port approx 100% bigger than previous production rotaries.
b. The side exhaust allows an exhaust port approx 30% bigger than previous production rotaries. Unfortuately, the port is not open as long as previous production rotaries and the exit path for exhaust is not as straight.
c. The intake manifold has been greatly improved to provide laminar airflow and uses 3 different length paths to tune the dynamic effect of the intake air pulses. This improves the supply of air to the engine for the entire powerband.

3. Better thermal efficiency
a. Better atomization of fuel due to ultra fine fuel injectors
b. More powerful spark due to higher power coils
c. Higher compression (unknown how high?) - [limited by sealing improvements and reliability]
d. Improved combustion stability/efficiency at low speed & light load due to no overlap.
e. Better thermal efficiency due to longer power stroke (exhaust port opens later)
f. Better thermal efficiency due to possible use of cermet (ceramic/metal hybrid alloy)?

4. Better mechanical efficiency
a. 14% Lighter rotors. Rotors will be approx 8.2 lb (9.54 * .86) leading safely to higher revs.
b. Shorter and lighter driveshaft. Carbon-fiber driveshafts are cool. :)

What else am I missing? I believe the side exhaust design was never used in the past because the peripheral exhaust offered a straighter path and led to greater power. While I'm sure that peripheral port rotaries with port jobs are capable of at least as much power as the renesis, we should congratulate Mazda on their R&D of the side exhaust port renesis since we can now have a rotary with larger ports AND greater fuel economy and emissions.

The future may yet hold a displacement increase for the rumored rx-7. Either by the addition of another rotor (3 rotor) or by something similar to how the 10a became the 12a (by increasing the width of the 2 rotors).

Brian

Great post Buger.

Yeah, good post Buger. I have to admit stunning ignorance with regards to how engines (and rotaries) work. I've got the basics, but little interest in the details. I like posts like this because they're far enough beyond my knowledge that I learn something, but not so far out there that I can't follow.

One question, I'm curious about the RX-7 displacement point. It seems to me that increasing the displacement of each rotor would be fairly difficult. Wouldn't that mean significant changes to the manufacture of the rotors, seals, and much of the rest of the engine? It seems that Mazda needs to keep manufacturing costs down more than other car companies, simply because they're so much smaller, even with Ford's help. Also, would this make the engine less responsive and less willing to rev, as I naively would assume?

I just had a thought, and perhaps this is a good place to ask. Could anyone describe to me how a 1.3 liter 2-rotor would differ from a 1.3 liter 4-rotor? In other words, if you cut the size of the rotors and increased the number, would it be more rev-happy and smoother, yet keep the power due to keeping the displacemnt the same? If they were smaller they could also be placed lower to lower the center of gravity, right? Or is there a good packaging reason to stay with 2 rotors? I seem to recall someone saying something about the eccentric shafts being difficult to place in a 3 rotor, am I completely off the ball here? I hope this question doesn't reveal my ignorance too much... :)

Thanks guys,

Originally posted by Rich
One question, I'm curious about the RX-7 displacement point. It seems to me that increasing the displacement of each rotor would be fairly difficult. Wouldn't that mean significant changes to the manufacture of the rotors, seals, and much of the rest of the engine? It seems that Mazda needs to keep manufacturing costs down more than other car companies, simply because they're so much smaller, even with Ford's help.

You are right about the costs and Mazda will probably not increase displacement in this way because of it. There is precedent in Mazda increasing displacement by using wider rotors though. I just threw it out there as a remote possibility since a recent article from Newsmotoring (http://newsmotoring.news.com.au/news/story_page/0,8269,5337129%255E21822,00.html) said the following:

"Mazda powertrain managers have ruled out the chance of turbocharging the RX-8 RENESIS rotary engine but admit they are looking at ways of increasing capacity of the 1300cc two-rotor engine, bringing more naturally aspirated power to the lightweight unit."

I was confused by the "looking at ways of increasing capacity" part because it would have been simpler to just say that they were looking at using a 3 rotor. In thinking about other ways Mazda could increase displacement, I found that they have widened the rotors in the past to increase displacement.

Also, would this make the engine less responsive and less willing to rev, as I naively would assume?

I think it would. The larger displacement would produce more torque but the tradeoff would be a lower redline due to the higher weight of the rotors.

I just had a thought, and perhaps this is a good place to ask. Could anyone describe to me how a 1.3 liter 2-rotor would differ from a 1.3 liter 4-rotor? In other words, if you cut the size of the rotors and increased the number, would it be more rev-happy and smoother, yet keep the power due to keeping the displacemnt the same? If they were smaller they could also be placed lower to lower the center of gravity, right? Or is there a good packaging reason to stay with 2 rotors? I seem to recall someone saying something about the eccentric shafts being difficult to place in a 3 rotor, am I completely off the ball here? I hope this question doesn't reveal my ignorance too much... :)

Hmm... I would think that a hypothetical 1.3 liter 4-rotor would rev higher. I think that the smaller rotors would exert much less stress on the eccentric shaft even if the total weight of the rotors were the same. I mean it's not like the entire weight of the rotors is moving up and down. :)

There are many added complexities though. I would also think that it would be exponentially harder to manufacture the parts because even finer tolerances would be needed on the miniaturized engine. If all of the world's car manufacturers were building rotaries, I'm sure there would be a wide variety of sizes. As it is now, Mazda is lucky they had enough financing to come out with any kind of new rotary. Of course, I am no expert on any of this stuff and I hope that I am corrected if I misunderstand anything.

It will be interesting to see how Mazda increases horsepower on the rumored rx-8 mps and the rumored rx-7. It is possible that turbocharging the renesis will not bring the same dramatic power increases as turbocharging previous peripheral port rotaries. I think that part of the reason is that the amount of air coming into the previous rotaries was the biggest limitation. The simple answer would have been to increase the intake port size but Mazda wouldn't have been able to market a car that couldn't pass the epa mileage guidelines (especially after the 70's gas crisis).

I read that the peripheral port design leads to much stronger "exhaust pulses" because of the straight path out of the engine and because the edge of the rotor effectively "pushed" the exhaust out of the port. The renesis has changed that by moving to the side exhaust port. Looking at the new design, we can see that the exhaust port is now larger and open for a shorter interval. This would seem to have strong "pulses" (with a longer interval between them though) even without the straight path. What effect would that have on a turbo?

Well Buger, you present excellent thought in the theories you've got...

Ya, increasing the width of the rotor would be the easiest way to increase displacement, but i suppose that Mazda's found a really favourable comprimize with the bore (width) and stroke (fixed: the area change when viewing the rotor between TDC and BDC) ratio with the 80mm width it's at.... supposing, however, that Mazda DOES increase the width again, i really don't think that the increase in mass would hurt RPM so much: the mass of one rotor right now is 8.62 pounds, and the rotor itself is 80mm wide, thus 1.08 pounds per mm of width. to make a big, HUGE inaccurate guestimation of the mass of a 90mm wide rotor would be a mere 9.70 lb., which is still really fricken' light, considering where rotor manufacturing technology was 10 years ago in the 13BREW.

i'm not convinced that a 1.3L 4 rotor would rev any higher than a 2 rotor, as the comprimize is greater amounts of friction, possibly (i suck at math, so i can't really calculate any of the data i'd need to know this is true or not; Grimace?? a little help??) a greater ratio of rotating mass to displacement (which i'm guessing wouldn't be a good thing)... but, on the plus side, the RELATIVE tolerances of some of the key components in the engine (supposing they're made in the same fashion of the same materials) increases as they're miniaturized: ie. apex seals, eccentric shaft... they have to deal with less force at once, right??

ya, the gains of adding a forced induction system on such an already sophisticated atmoshperic system would be less than the 13Bs (and variants)... that variable length induction runner technology is adapted from the 787B!! :D coolness...
and thus when you butcher those runners with a turbo system to slegde hammer the power in, so to speak, the net gains wouldn't be as high, and would probably take a chunk out of the low end torque (supposing they have to reduce the length of the fixed length runner)
IF they could come up with a variable length runner system, AND pop a turbo on there, i'd have NO IDEA what the hell that would look like, but wow...that would be a sight to see...

as per the differences on the exhaust side, the power stroke on the RENESIS is more efficient, as the force (which is pressure*area-pressed-against) is greater longer into the stroke, where the exhaust port is open later (thus pressure is held higher as the volume expands toward BDC: exhaust starts to be expired later...)
i suppose though, that because of that early opening in the 13B, the exhaust is expelled with greater velocity (smaller exhaust port, and the exhaust gases are at a higher pressure when expiration stage begins), and the pluse lasts longer than it does with the RENESIS, doesn't it?? so, that may feed the turbine side of a turbo better than the shorter pulses of the RENESIS, without any overlap either...
also, yes, the direction of flow is a little contorted now, but i wouldn't want to guess on how much that would affect output...

In regards to displacement,

Correct me if I am wrong but I seem to remember reading that a method of increasing displacement in rotaries is in scalloping out a portion of the rotary surface. Thereby increasing volume and decreasing weight.

Obviously this can only been carried to a point before the rotor loses strength. Anyone know if this was done to maximum potential in the Renesis?

Thanks Wakeech. I always like reading your posts too. :)

Originally posted by wakeech
Ya, increasing the width of the rotor would be the easiest way to increase displacement, but i suppose that Mazda's found a really favourable comprimize with the bore (width) and stroke (fixed: the area change when viewing the rotor between TDC and BDC) ratio with the 80mm width it's at.... supposing, however, that Mazda DOES increase the width again, i really don't think that the increase in mass would hurt RPM so much: the mass of one rotor right now is 8.62 pounds, and the rotor itself is 80mm wide, thus 1.08 pounds per mm of width. to make a big, HUGE inaccurate guestimation of the mass of a 90mm wide rotor would be a mere 9.70 lb., which is still really fricken' light, considering where rotor manufacturing technology was 10 years ago in the 13BREW. [/B]

I actually found that Mazda has increased the bore (width) at least twice in the past. The 10a was originally 60mm wide. Mazda increased the width of the 10a to 70mm for the 12a. Mazda then increased the width of the 12a to 80mm for the 13b. The mass of the last generation rotors was 9.54 lbs and the fd3s had a 8000 redline (9000 tach). Mazda says that the renesis rotors are 14% lighter so they should be approx 8.2 lbs with a 9000 redline (10000 tach). Using the same guesstimation method, a 90mm width renesis rotor would weigh approx 9.225 lbs. Still pretty fricken' light and the redline of a hypothetical renesis with 90mm rotors should be somewhere between 8k and 9k.

i'm not convinced that a 1.3L 4 rotor would rev any higher than a 2 rotor, as the comprimize is greater amounts of friction, possibly (i suck at math, so i can't really calculate any of the data i'd need to know this is true or not; Grimace?? a little help??) a greater ratio of rotating mass to displacement (which i'm guessing wouldn't be a good thing)... but, on the plus side, the RELATIVE tolerances of some of the key components in the engine (supposing they're made in the same fashion of the same materials) increases as they're miniaturized: ie. apex seals, eccentric shaft... they have to deal with less force at once, right?? [/B]

You're right that there are many factors. Maybe an mechanical engineer can tackle this one. :)

ya, the gains of adding a forced induction system on such an already sophisticated atmoshperic system would be less than the 13Bs (and variants)... that variable length induction runner technology is adapted from the 787B!! coolness...
and thus when you butcher those runners with a turbo system to slegde hammer the power in, so to speak, the net gains wouldn't be as high, and would probably take a chunk out of the low end torque (supposing they have to reduce the length of the fixed length runner)
IF they could come up with a variable length runner system, AND pop a turbo on there, i'd have NO IDEA what the hell that would look like, but wow...that would be a sight to see... [/B]

A turbo renesis will definitely not be as "elegant" as the efficient na renesis. Part of the appeal of the rotary is from its elegant design without valves, cams, timing chains, etc. Then again, there are a lot of people who don't give a @#$$ about elegance and just want more peak torque and power! :)

as per the differences on the exhaust side, the power stroke on the RENESIS is more efficient, as the force (which is pressure*area-pressed-against) is greater longer into the stroke, where the exhaust port is open later (thus pressure is held higher as the volume expands toward BDC: exhaust starts to be expired later...)
i suppose though, that because of that early opening in the 13B, the exhaust is expelled with greater velocity (smaller exhaust port, and the exhaust gases are at a higher pressure when expiration stage begins), and the pluse lasts longer than it does with the RENESIS, doesn't it?? so, that may feed the turbine side of a turbo better than the shorter pulses of the RENESIS, without any overlap either...
also, yes, the direction of flow is a little contorted now, but i wouldn't want to guess on how much that would affect output...[/B]

You make a good point that the earlier opening of the 13b exhaust would be expelled when the pressure is higher. I hadn't really thought of that before. :)

Two unknowns about the renesis that I am eagerly awaiting info on are the compression ratio and if there will be a new coating for the engine housings. I think it was one of the Autobild articles that mentioned something about ceramic. One of the disadvantages of the rotary is the lesser thermal efficiency than the piston engine (because of the larger surface area of the combustion "chamber"). I wonder if Mazda is going to be using something like the "cermet" that they used on the 787b? :)

Brian

Originally posted by Aesculapius
In regards to displacement,

Correct me if I am wrong but I seem to remember reading that a method of increasing displacement in rotaries is in scalloping out a portion of the rotary surface. Thereby increasing volume and decreasing weight.

Obviously this can only been carried to a point before the rotor loses strength. Anyone know if this was done to maximum potential in the Renesis?

Hi Aesculapius,

See my previous post about how Mazda increased displacement from the 10a to the 12a to the 13b by increasing the width of the rotors. Mazda has also added another rotor to increase displacement.

I think that Mazda changes size of the depression on the rotor to change compression? Perhaps somebody that knows more can explain how Mazda changes the compression as it would seem that lowering compression in this manner would also increase displacement marginally? (or vice versa)

Who here can give some input on how Mazda changes the compression of rotaries?

Brian

yup, the bathtub is exactly what you think it's for: controlling the compression ratio, as well as creating a cumbustion "chamber" (or so they describe it) for a good place for the flame front to form, and give the plugs some clearance... BUT, on the port side of the engine, this channel is a big reason emissions were smoked with tons of HC's flowing down to the exhaust port (kinda have to go through it to get there), after the inspiration port was given a wicked street and bridge port...

let's see.... some of the ongoing turbo discussions that were happening when i first joined the board were throwing around compression ratios of 10.5:1... i dunno if that's official or not (Boo??), or some guy just guessing... if it's a guess, that's exactly what i'd guess too :p

OH!! ceramics, forgot to say something abotu that before.... you know that iron sleeve in the expiration port of the 13B block?? i heard about the RENESIS incorperating ceramic materials into port linings, or around the block, or something??? the impression that is in my mind is that it was used as a sleeve similar to that iron one in the 13B...

here's something that's been buggin' me for a while: i've thought about it for a while... that 30% savings in mass, does that imply that the iron-intensive bits in the block "sandwich" have been switched to aluminum based alloys???

Wakeech,

I think that the side housings are still going to be made of iron. As I understand it, the "30% lighter" largely comes from the lack of turbos and associated hardware. I think they include the weight of the turbos when refering to the weight of the 13B-REW.

As far as keeping the variable length induction system if a turbo is added, I don't really see that as much of a problem. You wouldn't have to replace the intake manifold to add a turbo.

Originally posted by wakeech
yup, the bathtub is exactly what you think it's for: controlling the compression ratio, as well as creating a cumbustion "chamber" (or so they describe it) for a good place for the flame front to form, and give the plugs some clearance...

I can understand how the "bathtub" size could control compression but wouldn't a bigger bathtub marginally increase displacement also? Shouldn't low compression rotors give you a displacement of something like 1309 cc rather than 1308 cc? Or is the difference in size so small that it makes less than 1 cc of difference in displacement?

let's see.... some of the ongoing turbo discussions that were happening when i first joined the board were throwing around compression ratios of 10.5:1... i dunno if that's official or not (Boo??), or some guy just guessing... if it's a guess, that's exactly what i'd guess too :p

I think that the compression ratio is one of the factors that Mazda was playing around with when coming up with the renesis. The higher fuel efficiency and power of higher compression ratios needed to be balanced with long term reliability concerns. The rx-8 has to be reliable. (Perhaps Mazda will be a little more aggressive on a next gen na rx-7?) The compression ratio is probably one of the main factors that brought the projected power from 280 hp to 250 hp. Of course, one of the advantages that rotaries have over piston engines is that lower octane gas can be used for any given compression. :)

OH!! ceramics, forgot to say something abotu that before.... you know that iron sleeve in the expiration port of the 13B block?? i heard about the RENESIS incorperating ceramic materials into port linings, or around the block, or something??? the impression that is in my mind is that it was used as a sleeve similar to that iron one in the 13B...

The low thermal conductivity of ceramic coatings could be the perfect way to counteract the lesser thermal efficiency of the rotary due to it's relatively large surface area.

here's something that's been buggin' me for a while: i've thought about it for a while... that 30% savings in mass, does that imply that the iron-intensive bits in the block "sandwich" have been switched to aluminum based alloys???

I think I read that the weight savings was mainly from the turbo related components. Of course, the rotors are 1.33 lbs lighter each. Who knows what other components were lightened?

Brian

Originally posted by Buger
Of course, one of the advantages that rotaries have over piston engines is that lower octane gas can be used for any given compression. :)


Why? The specs/fuel requirements of other rotaries seems pretty much in-line with similar piston engines. I can see how the twin-plugs might help, but I thought those were just to compensate for the inherent inefficiencies of the combustion chamber shape in a rotary.

Originally posted by Macabre
Why? The specs/fuel requirements of other rotaries seems pretty much in-line with similar piston engines. I can see how the twin-plugs might help, but I thought those were just to compensate for the inherent inefficiencies of the combustion chamber shape in a rotary.

Hi Macabre,

I read that NA rotaries are less susceptible to pre-ignition and detonation because of their design. In the rotary, the intake and exhaust "strokes" are in separate areas of the engine than the power "stroke" whereas in a piston engine, all of the strokes are in the same area. This supposedly lessens the chance of ignition of gases when it isn't supposed to happen.

One of the marketing points of the rotary in it's early days was the ability to use lower octane fuel. One of the major concerns about the rotary after the gas crisis in the mid-seventies was it's fuel economy. The rotaries had comparatively better mileage at high revs than low. The entire reason the US has EPA mileage ratings for both city AND highway is because of Mazda pushed for the dual ratings. :) I read that one mitigating factor that the rotary had during the gas crisis was that it could run on 70 octane gas. Of course this wouldn't help the general public because the lowest octane gas available at the pumps was something like 85 (US uses ron+mon/2). The general rule for unmodified na rotaries is to use the lowest octane you can get.

The ability of the rotary to run on low octane gas was important because leaded gasoline was phased out and replaced by unleaded. The properties of lead were great for engines because it prevented detonation, pre-ignition and supplied lubrication. Unfortunately, the properties of lead are not as great for people.

Brian

Hmm. That's interesting. Sounds good in theory, but in practice I don't know. I do know that the third gen's required premium (91+?) fuel, similar to piston engines of simialar displacement and boost, with a 9:1 CR, but that's not necessarily a representative example. I can definitely see the point about pre-ignition being reduced, since there shouldn't be any hotspots to ignite the mixture in the portion of the chamber used for intake (although some could form on the rotor itself?). I don't see how the risk of detonation would be reduced though. Anyways, thanks for the info.

These conversations will be far more insightful when we have the final specs on the renesis and the RX-8 :D

Originally posted by Buger
I can understand how the "bathtub" size could control compression but wouldn't a bigger bathtub marginally increase displacement also? Shouldn't low compression rotors give you a displacement of something like 1309 cc rather than 1308 cc? Or is the difference in size so small that it makes less than 1 cc of difference in displacement?
I found the answer to my own question. :)

http://members.tripod.com/~hardebeck/engine.htm has the below info:

"Rotary engine displacements seem small when compared to piston engines of similar power. In fact, both displacements are measured the same way. Displacement is the sum total of positive combustion chamber volume increases for one complete revolution of the main shaft (crank or eccentric). In a piston engine, this means the total amount of space swept by its pistons. In a rotary, it is easiest to think about the difference between the maximum and minimum volumes for a single chamber multiplied by the number of rotors (where each rotor has 3 chambers). Remember that the rotor actually revolves at one third the speed of the eccentric shaft, which is the reason only one chamber's displacement is used in the calculation."

Since displacement is the sum total of positive combustion chamber volume increases, a bigger "bathtub" does not affect displacement.
Originally posted by Macabre
I can definitely see the point about pre-ignition being reduced, since there shouldn't be any hotspots to ignite the mixture in the portion of the chamber used for intake (although some could form on the rotor itself?). I don't see how the risk of detonation would be reduced though.
I was using the terms pre-ignition and detonation interchangably when they are very different indeed. Thanks for the link (http://link.sandiego.com/scripts/wheelbase/message.idc?passin=297) which explains the difference between the two very well.

The same site also has an article (http://link.sandiego.com/scripts/wheelbase/message.idc?passin=334) about how a rotary is much less subject to pre-ignition than a piston engine:

"First, hydrogen is subject to preignition. A conventional piston engine converted to hydrogen use tends to light off its incoming charge on hot exhaust valves or spark plugs...

...The HR-X is powered by one of Mazda's Wankel engines, which neatly sidestep the hot-spot problem by having separate areas for mixture induction and combustion."

Here is a question for some of the mech engineers (tallguylehigh, pelucidor, ...) and other smart people on the forum. What other changes do you think would be made to increase power on the rotary in the rumored 4th gen rx-7?

The specs for the rx-evolv had 280hp @ 9000 rpm. One of the things that Mazda did to make the rx-8 a little more conventional is to focus on hp at lower revs. Mazda may have also lowered the compression a little bit (from the rx-evolv) for improved reliability.

What other changes could future rotaries have?

The current renesis has no overlap. While this is great for lower revs, I read that "scavenging" effect of overlap improves power at higher revs. How about a small peripheral port exhaust that opens at high rpms?

What about the miller cycle rotary which was under development in the 90's? The belt driven lysholm compressor used in the Millenia was more efficient at compressing air than any engine could be. Could this be the much speculated about intercooled & "supercharged" rotary? This could increase fuel economy under light load conditions by reducing pumping losses while adding hp & torque across the powerband also.

I remember that our much respected Boowana mentioned that he thinks "a 300HP for the Mazdaspeed version is not out of the question". (http://www.rx8forum.com/showthread.php?s=&threadid=919&perpage=15&pagenumber=4)

He also mentioned that "Robert Davis, a VP at Mazda stated that there will be a Mazdaspeed version of the RX-8 with 300 HP but did not say that it was turbocharged." (http://www.rx8forum.com/showthread.php?s=&threadid=983&highlight=300) Was this another hint? :)

Brian

I think the Renesis makes more power because the intake port are larger and open earlier. I think they will be able to be bridge ported if the exhaust port closes close to TDC or before because you would half to do this so there would be no overlap with the intake port. TDC or Top Dead Center is when the rotor is in the postion to make the smallest chamber. There is only one true TDC and it is on the Spark plug side of the housing but there is one the intake and exhaust side too. Think about the power possible with a bridge ported rotary. I think there would be no down sides to it as there is with rotarys to date.

Originally posted by MWG
I think the Renesis makes more power because the intake port are larger and open earlier. I think they will be able to be bridge ported if the exhaust port closes close to TDC or before because you would half to do this so there would be no overlap with the intake port. TDC or Top Dead Center is when the rotor is in the postion to make the smallest chamber. There is only one true TDC and it is on the Spark plug side of the housing but there is one the intake and exhaust side too. Think about the power possible with a bridge ported rotary. I think there would be no down sides to it as there is with rotarys to date.

Hi Mwg,

Welcome to the forum. The increased intake port size is one of the factors listed in my original post. I don't believe it opens earlier though. From what I have read, the port timings for the new side port are below:

Primary intake .....opens 32° ATDC .....closes 40° ABDC
Secondary intake opens 32° ATDC .....closes 30° ABDC
Aux. intake ..........opens 45° ATDC .....closes 80° ABDC
Exhaust ..............opens 50° BBDC .....closes 23° BTDC

The intake port timings are exactly the same while the exhaust port opens 25 degrees later (increased thermal efficiency) and closes 71 degrees earlier.

Hopefully somebody can confirm this information?

Also increasing the port size will probably not have quite the same effect as it had on previous rotaries.

Brian

interesting idea you've come up with there Boogs, with the auxillary exhaust port on the perhipheral side... hmmm.... but i think our friend MWG may be onto something, with the bridge port idea... maybe with heeeeeeeeaaaaaaavvvvvvyyy reinforcement of the bridge itself, and not going too aggressively (making the bridge too thin, or not leaving a very very thin "fence" to keep the apex seals squarely on the rotor housings) for maximum width of the port, and didn't go for max overlap, or just bridging on the secondary inspiration ports (the 5th and 6th controllable ones), they could increase factory hp by double digits at peak numbers, without really comprimizing much other than emissions...

i was thinking, what if they had secondary ports, ie "5th and 6th" ports for the expiration side... when i think about trying to pipe a perhipheral version of the same, it'd be a real mess of spaghetti, so i think maybe the side would be more easily accomplished....

hmmmmmm.... :) interesting. i wonder how much Mr. Joe Average could screw around with this block without totally f***in' the whole thing... probably not much... :(

Originally posted by wakeech
interesting idea you've come up with there Boogs, with the auxillary exhaust port on the perhipheral side... hmmm....

A small peripheral intake port that opened at high rpms would probably be more practical than the exhaust one although either one would affect emissions a little bit.

It is also possible that there were improvements to the apex seals since they no longer have to travel over peripheral ports now?

Brian

oh yes!! that also may be true... they MIGHT be gettin' away with softer and lighter seals, as even though they were supported on either side of the gap as they travelled over the exhaust port in all pre-RENESIS layouts, there'd still be some wear on the leading edge of the seal as the port "fully opens" and "fully closes", yes??
those softer and lighter seals would obviously provide better sealing (higher degree of emissions friendliness), and maybe even lend themselves to prolonging good engine compression, eh?? wow... good one...

hey guys!! EVERYONE, welcome back.

PLEASE CHECK THIS OUT AND RESPOND, 'cause it's mega mega cool...

over the break i took to posting on the (ugh) Autoweek forum, and there're two or three really smart fellows over there, but they're all muscle-heads... support for the rotary was absolutely insane!! lots and lots... everyone thinks it's cool...

to get back to what i was gonna say, one of the smart and resourceful guys over there found out (and calculated) some really neat info which goes into why the rotary engine (our RENESIS) makes so much power from such little displacement, and is so keen on revving so high.

i've not gone back and read everything, 'cause it's too much, but i've addressed Formula1 engines in many of my posts (not necessarily in this thread). to hit 19k rpm, the engineers have designed the pistons with as wide a bore, and as short a stroke as they can (limited by the fact that the valves have to FIT into the combution chamber), with horribly horribly oversquare designs. the short stroke and broad piston face lets them rev very very high (short distance to move over), and lots of force (as force = pressure * area) per stroke, which together add up to immense power.

back to the rotary. can you guess how oversquare this sucker is?? can you?? the stroke is 1.575 in (40 mm)... that's it. 654cc displacement, 40mm bore. think about that.

the "bore", calculated as if it's a piston (which it obviously isn't), is the full volume, divided by pi, square rooted (that's to the half power), times two (if my mental algebra holds up...).

the "bore" of the 80mm wide rotors of the 13B and now RENESIS are in the order of 5.681 in (144.3mm)!!!!!!! :eek::eek::eek::eek:

unbelieveable, but true. that short stroke and long rotor side really add up to some amazing oversquareness in this engine.
Boowana just said yesterday that the RENESIS was tested at 17k rpm...
LOOK OUT F1!! ;) heh heh heh...

Compression ratio in the production rx-8 is 10:1 which is marginally higher than the 9.7:1 of the previous NA rotary. I assume the compression ratio wasn't engineered higher because Mazda wanted the RX-8 to be incredibly reliable to counter the perception that many people have after the twin-turbo 3rd gen.

Mazda can produce more horsepower with this engine very easily...

Brian

The "bathtub" size has no effect on displacement because displacement is determined by the difference in volume between the combustion chamber at its largest and smallest. By increasing the size of the bathtub you increase combustion chamber volume in all cycles, which does not affect displacement. It's like adding the same amount to both sides of an equation, the difference is still the same.

A 1.3L 4 rotor wouldn't rev as well as a 1.3L 2 rotor for a very important reason. While smaller, lighter rotors would be more eager to rev, a longer eccentric shaft is more susceptible to flex at high RPM. I have serious doubts about an eccentric shaft that long holding up without using highly exotic materials.

I understand that Mazda is developing an engine with the same trochoidal dimensions but with the rotor width increased to 90 mm, giving a displacement of 1477cc.

Since the old 12A, 13B, 20B designations are going by the wayside, I expect it the 1.3L and 1.5L to simply be called the Renesis 1.3 and Renesis 1.5, respectively.

Originally posted by SmokingClutch
The "bathtub" size has no effect on displacement because displacement is determined by the difference in volume between the combustion chamber at its largest and smallest. By increasing the size of the bathtub you increase combustion chamber volume in all cycles, which does not affect displacement. It's like adding the same amount to both sides of an equation, the difference is still the same.

A 1.3L 4 rotor wouldn't rev as well as a 1.3L 2 rotor for a very important reason. While smaller, lighter rotors would be more eager to rev, a longer eccentric shaft is more susceptible to flex at high RPM. I have serious doubts about an eccentric shaft that long holding up without using highly exotic materials.

I understand that Mazda is developing an engine with the same trochoidal dimensions but with the rotor width increased to 90 mm, giving a displacement of 1477cc.

Since the old 12A, 13B, 20B designations are going by the wayside, I expect it the 1.3L and 1.5L to simply be called the Renesis 1.3 and Renesis 1.5, respectively.
Hi Smokingclutch,

Nice post. I'm aware that the bathtub size has no effect on displcement though as I answered myself at the bottom of the first page of this thread. :) I actually sent a message to howstuffworks.com so that they can correct their article on the rotary but I never got a response.

You are right that a longer eccentric shaft would cause more flex *if the rotors were the same size*. The main reason why the renesis is allowed to rev higher is because the rotors are 14% lighter so they don't cause as much e-shaft flex. Of course a 4-rotor 1.3L engine would have rotors that are verry light and would not cause anywhere near the flex of previous 9.54 lb rotors.

Whatever the case, there is new information out there to be found. I am past my previous ruminations. :)

Brian

Great discussion guys. This belongs in techno forum asap! :D

here's some stuff i wrote in my thread entitled "Ahhh, the "weird" Bevel", and since it appears to me that very very few people have taken the time to read it, AND this thread is now in this section, i will simply snip and paste... :)


ladies and gents, Sputnik has posted some rather beautatious pics of the RENESIS cut-away model at the Detroit show Boowana is storming, and gives us a rather excellent view of the new spec rotors...

here's the link: Boowana's Beautatious Pics 'o' the RENESIS (http://www.rx8forum.com/showthread.php?s=&threadid=1603)

i've heard of this trick on rotary tuning pages, where the leading sides of the rotor are ground away (corresponding with the side inspiriation ports) to advance the intake timing without cutting into the perhipheral housing with an extended J-Port ("Monster" port)...
so, this means that to really get "Zero" overlap, Mazda could advance the intake timing to the point where the rotor is JUST coming around to TDC when it starts to open (that's like, earlier than piston engines friends)... COOL BEANS TO THE MAX!! :D

of course, with the "correct" porting you could advance the timing wellllll before TDC, not that it'd be a good thing, but you could... :p

here's a link i made not moments ago (well, okay, a bunch of moments together) about ignition and stuff... mmm mmm, noobilicous... :DStuff on Rotary (13B) Ignition... (http://www.rx8forum.com/showthread.php?s=&postid=20206)

now, for those who're new, i'm Andrew, and all that i know i cannot back up with solid learning... i'm a 19 year-old university student, studying economics, and i yearn to touch wrench to bolt, but as of yet haven't... ;)

Turbodyne and Garret are working on mass producing an Electric TurboCharger (e-charger).

Nissan is working on Bi-E-Charger for the next Skyline-GTR...

If TurboCharging the RX-8 is very difficult, how about an E-charger?

Also, I am very interested in the MPS RX-8 with 300 HP...

My CLS does nw low 14s in 1/4mile with all bolt-ons (more than 300HP @ crank)..Therefore, a low-rpm Hi-Torque is a must...

Hopefully we can see some 200+lbft of Torque on a RX-8 engine...

RX-8 is a very cool car... :D

on your question about "adding torque", well, there are a few ways you can do this: increase the displacement (the good ol' American way), increase the volumetric efficiency with some kind of magical inspiration and expiration system, or using forced induction get the same result (more air and fuel to burn at once)...

a wider rotor'd version of the RENESIS has been speculated, which would go a long long way to upping the low rpm torque, but this doesn't answer your question.

to increase the volumetric efficiency in an all-motor application, what you need is a system of inspiration and expiration that will automatically adapt to the needs of the engine. at low rpm, the induction runners must be long and small in diameter to maximize this, as there is an optimum velocity for the air being drawn in at a certain rpm, and this is affected by the amount the engine is trying to suck in per second (obviously determined by rpm), and the diameter of the induction runner. also, the length must be tuned to the rpm, as the positive and negative pressure waves (as the port is opened and closed) can be used to "suck" in more air at the opening (during a negative pulse), and can somehow deaden the effect of a positive pulse (?? Boogs??), i think... in any case, to do this at 100% efficiency, you'd need to have runners on both the inspiration side and the expiration side changing their diameter and length to every change in rpm, throttle position, and load. Mazda's done well, and has a system of three different RUNNERS ( not three different intakes), of three different lengths which are selected by the cpu to maximize efficiency.

as for forced induction, it's a fairly simple equation in theory, and unbelievably complex in practice (at least at the high-dollar, high-performance level). more air, plus more fuel, equals more pressure in the combustion chamber, which equals more force on the eccentric shaft, which equals more torque. more torque at the same rpm equals more power, and you go faster.
can you do it on the rotary?? why not?? no room?? if you were serious as a heart attack about making an 8 fast in the 400 (meters, that is ;)) throw stuff out of the engine compartment, onto the ground or into the trunk, or whatever you like. can you make it work with the variable length induction runner system that Mazda's put on the RENESIS?? depends. a supercharging system, i could see that working (specifically your e-charger, as it'd be easier to locate about the engine), but turbo charging?? i think you'd be asking for it, hard, and exactly where i'm guessing you're not ready for it... that's right, in the wallet. ;)
seriously, it'd be a miracle for anyone to get the systems to work together, never mind fitting it in any vehicle short of a truck (a big, big truck). if you were gonna turbo the RENESIS, you'd probably throw the stock induction system in the bin, and pick a single length and diameter for the impeller to blow through. this'd absolutely kill your low-rpm torque (obviously), but you'd be pumping the horses up top.
i've just gotta add this: backpressure is bad, but that doesn't mean a bigger tip for your exhaust system is necessarily going to increase efficiency. think of the velocity, and this'll make sense. please, don't be a tail-pipe farter.

ah yes, now, as for adding speed in the quarter mile, it's as simple (as Rich and Sputnik like to say) as "adding plenty of lightness". the RX-8 will probably weigh between 2850 and 2950 as a rough estimate, which is considerably less than your CL with all that other stuff you've got on it (the sunroof, spoilers, etc etc)... how much does it wiegh?? probably more than the 3470lb estimated curb weight that Acura quotes. unless you already do this, you could shave a tenth or two off your ET by having less than a quarter tank of gas in it (with some in a can for a top up to get home), and leaving everything that you can take out of it back at the staging lane...

back onto the topic of the RENESIS, please remember this: it's a 1.3L engine. i'll write it again, because i like that number: it's 1.3L in displacement. if you didn't read it before (i suggest you do), this engine is gargantuanly oversquare (40mmx144mm) and it STILL makes 159 lb/ft of torque at peak, with 90% of that being made from 3000 to redline (right?? i can't remember... Boogs, you know)... even factoring in that it does have twice as many power strokes per revolution in an equally displaced 4-stroke piston engine, you'd still only be at 2.6L corrected. here's a little piece of info from the TSX (the latest Acura sports sedan to be offered):

The TSX features a 2.4-liter DOHC, i-VTEC engine that generates 200 horsepower at 6,800 rpm and 166 lb-ft of torque at 4,500 rpm.

think about that... horribly oversquare (more so than an F1 engine, i'd wager... they don't give out borexstroke measurements, so you can't be absolutely sure), an fundamental engine design which has existed for about half the life of the piston engine, making such incredible power at high rpms, with a wide power band (quite linear), and still makes nearly as much PEAK torque as one of the best 4-bangers in the world.

it's STILL one hell of an engine... :D

Originally posted by NashuaCLS
Nissan is working on Bi-E-Charger for the next Skyline-GTR...

i dunno if the next GT-R is gonna be a Skyline... you've seen that thing, right??? nice car, but... i need my :rolleyes: !!! :p

ahhhh, forgot forgot forgot...

torque at the flywheel doesn't mean all that much, because the flywheel doesn't push your car along, the wheels do, yes?? well, the gearing of the RX-8 is supposedly quite aggressive, which could possibly translate into sub 6.0s 0-60mph times (by Buger's fairly generous estimation in CarTest).

200 lbft of Torque from Renesis does not hurt? maybe the MPG...but that is oKay if your bills would increase like $100 per year.

It is nice to improve on excellent car to start with...a 13.5s $35K car that handles great is a great idea...

BTW what is the competion for RX-8 (less than $35k)

WRX STI..
EVO lanncer...
SRT-4...
S2000 Coupe/Roadster
G35c
CLS-6 speed.

The first 2 would beat the RX-8 in all categories excpet the aspect of luxury

The SRT-4 would accelerate and it is rummored to be a good handler... (It could be true but not sure about it) forget about luxury.

S2000 is as fast as the RX-8 Excellent handler (but 2 seater)

G35 Luxury and Performace and even Beats the 330Ci in every aspect

CLS-6 Excellen Acceleration... Front Heavy but suspesion mods (sway bars a lowering springs and good set of tires, headers, CAI) Still great 14s car for less than $35k!


Mazada has to convence the smart buyer that the RX-8 is an outstanging car and value and performance included..

Not Bashing the RX-8... I like the car.. howver, why not give light weight rims and Brambo Brakes... and bit more Performace ...at least as on option... I expect that such goodies would be on the MPS version... :D

Let me try to answer all your questions...

First of all, comparing an AWD or FWD car to the RX-8 is a bad comparison... they have very different driving characteristics. Sure speed and grip are noted with AWD but you don't get the feedback you do with RWD, nor can you gas it and get the tail out for some fun drifting (though I'd never do that! :)) That takes the STi and Evo out of the comparison.

The CL-S, RSX-S, SRT-4, all FWD. Great handles AS front wheel drivers, but face the fact.. you have no control over that rear end. Driving wheels in the back are generally better for track use (which is why Miatas beat lots of cars at an Auto-X). So toss them out.

Now here are the right comparisons. 330i, G35 Coupe/Sedan, 350Z, S2000... these are the competing vehicles.

Let me first say that the G35 doesn't beat the 330 in much anything other than price and accelleration (and with the new 330's engine, doesn't do that any more either). Braking is better, steering feedback is better, handling is better.. skidpad... etc etc... If you drive the two cars back to back (I did one day) you will understand. Also, the G35 (and I don't care what people say) has a cheezy interior with bad materials thruout. While Mazda may not be BMW quality, the day I drove the G35 and stepped back into my Millenia, I was a happier camper as per the interior materials. But I digress..

You say the RX-8 needs Brembo brakes? Given the data available, and mathematical computations, the RX-8 will stop faster than an M3 can. Faster than the 350Z (With the Brembos). Brembos are great for the company that wouldn't like to invest money in developing their own braking system for whatever reason. BMW develops their own and as a result has better braking in class because they design their brakes for the car. Other companies that use Brembo get a 'fitted' design that isn't always ideal and while it may stop fast, a properly manufactured design from the company is usually better. So let's understand first out of all the cars, the RX-8 will have the best braking.

Next comparison will be accelleration and for lack of patience on this question, I'll simply say that yes, it's in the middle of the pack. It should beat the 330i (current engine) to 60 and in the quarter but the 350Z will probably beat the RX-8. The G35 Coupe with the 6 speed and RX-8 will be neck and neck (this is a guess, but a good one I think). Keep in mind that for most of the rev range aside from low end (3-5k) the RX-8 exerts more torque than the G35 and 350Z. That's where track driving becomes fun :)

Luxury I'll put the RX-8 second. Since they decided not to go with the cheezy silver trim the Mazda6 has in it and the G35 has in it, the car is the better for it. I think that BMW will be #1 here, with RX-8 not too far behind.

In the end the 'smart' buyer (as you put it) will see that the RX-8 can run with the best if not out perform them, has an appealing shape both inside and out, isn't cheap like the 350Z or G35 inside, and doesn't cost as much as any of them. That is why the RX-8 is a good car and in my mind, the best car overall in the pack. Granted I think the 330 will be a better handler (or maybe I'll be proven wrong with final production reviews coming out..), but for about 10 grand less... who can argue?

Bravo herc Bravo. that was excellent, i think you have summed it up quite nicely. totally agreement :cool:

Let me say this ... What does the MPS RX-8 should provide to make it a "smart buy"?

BTW, discounting 4WD , AWD is a mistake...

Handling, grip, and winter perforance for us living in the north... is a MUST.

Second rally cars are about performance, great traction, great handling...

WRX Stil and EVO are excllent track cars if you can forget about the luxo factor...

Yeah,... I forgot about the Z350 ... another excllent track car that handles like a Porsche...

Originally posted by NashuaCLS
Let me say this ... What does the MPS RX-8 should provide to make it a "smart buy"? Stiffer suspension, wider rotors (more power), lighter materials.

So you get handling and power upgrades to the MPS. Same thing as if you jumped from a 330i to an M3. Handling and power.

Originally posted by NashuaCLS
BTW, discounting 4WD , AWD is a mistake...

Handling, grip, and winter perforance for us living in the north... is a MUST.

Second rally cars are about performance, great traction, great handling...

Discontinuing 4WD,AWD is NOT a mistake. These do not necessairly improve handling or grip. Suspension design and tires do that. Awd actually adds unnecessary weight and drivetrain complexity. Even the 911 Turbo system is primarily RWD and only sometimes it adjusts power to the front. The only time awd is beneficial is in powering out of a corner in slippery conditions. 99% of people do not NEED to do that while it's raining/snowing.. we're not rally racers. AWD would help in the winter, yes.. But a rwd car with dedicated winter tires can outperform an AWD car with all season tires on. Personally I can live without the added cost, weight and maintenance for awd.

Originally posted by Hercules
Let me try to answer all your questions...

First of all, comparing an AWD or FWD car to the RX-8 is a bad comparison... they have very different driving characteristics. Sure speed and grip are noted with AWD but you don't get the feedback you do with RWD, nor can you gas it and get the tail out for some fun drifting (though I'd never do that! :)) That takes the STi and Evo out of the comparison.

The CL-S, RSX-S, SRT-4, all FWD. Great handles AS front wheel drivers, but face the fact.. you have no control over that rear end. Driving wheels in the back are generally better for track use (which is why Miatas beat lots of cars at an Auto-X). So toss them out.

Now here are the right comparisons. 330i, G35 Coupe/Sedan, 350Z, S2000... these are the competing vehicles.

Let me first say that the G35 doesn't beat the 330 in much anything other than price and accelleration (and with the new 330's engine, doesn't do that any more either). Braking is better, steering feedback is better, handling is better.. skidpad... etc etc... If you drive the two cars back to back (I did one day) you will understand. Also, the G35 (and I don't care what people say) has a cheezy interior with bad materials thruout. While Mazda may not be BMW quality, the day I drove the G35 and stepped back into my Millenia, I was a happier camper as per the interior materials. But I digress..

You say the RX-8 needs Brembo brakes? Given the data available, and mathematical computations, the RX-8 will stop faster than an M3 can. Faster than the 350Z (With the Brembos). Brembos are great for the company that wouldn't like to invest money in developing their own braking system for whatever reason. BMW develops their own and as a result has better braking in class because they design their brakes for the car. Other companies that use Brembo get a 'fitted' design that isn't always ideal and while it may stop fast, a properly manufactured design from the company is usually better. So let's understand first out of all the cars, the RX-8 will have the best braking.

Next comparison will be accelleration and for lack of patience on this question, I'll simply say that yes, it's in the middle of the pack. It should beat the 330i (current engine) to 60 and in the quarter but the 350Z will probably beat the RX-8. The G35 Coupe with the 6 speed and RX-8 will be neck and neck (this is a guess, but a good one I think). Keep in mind that for most of the rev range aside from low end (3-5k) the RX-8 exerts more torque than the G35 and 350Z. That's where track driving becomes fun :)

Luxury I'll put the RX-8 second. Since they decided not to go with the cheezy silver trim the Mazda6 has in it and the G35 has in it, the car is the better for it. I think that BMW will be #1 here, with RX-8 not too far behind.

In the end the 'smart' buyer (as you put it) will see that the RX-8 can run with the best if not out perform them, has an appealing shape both inside and out, isn't cheap like the 350Z or G35 inside, and doesn't cost as much as any of them. That is why the RX-8 is a good car and in my mind, the best car overall in the pack. Granted I think the 330 will be a better handler (or maybe I'll be proven wrong with final production reviews coming out..), but for about 10 grand less... who can argue?


I think people tend to overyclassify cars into ridiculously rigid categories. Now, that's not to say an individual shouldn't have their individual preference of cars to choose from, but I do not think its unfair to compare fun-to drive cars that are within a somewhat similar price range that a fair number of people will cross-shop. Based on objective tests (though IMHO of less importance than subjective feel), I think the RX8 will have a difficult time with the EVO, STI, 350Z and the S2000. However, this remains to be seen.

I do agree with you that AWD cars will have a much different (but not necessarily less fun) feel. The same goes for a FWD car.

I will agree, that in general RWD cars give more potential for sportiness (though some could argue this point for AWD too), but I think design execution and tuning are much more important. Hell, a RWD car can be desinged to understeer. Yes, you could upgrade the suspension, breaks, etc. to compensate for this, but to me it just seems like something that shouldn't need to be done (at least right away) when you throw $30K down. I would have taken an integra type r over most similarly priced RWD sports cars of its time (at least in terms of handling) because of its high limits, confidence inspiring cornering, and all over hard-core, no-nonsense nature.

My biggest concern has and still remains the possibility of its design lacking this soul or spirit. Like it or not, different design goals have been merged to form what we know as the RX8. Until, I see real proof that this car lives up to its claims, I will remain skeptical.

Originally posted by NashuaCLS
Let me say this ... What does the MPS RX-8 should provide to make it a "smart buy"?

BTW, discounting 4WD , AWD is a mistake...

Handling, grip, and winter perforance for us living in the north... is a MUST.

Second rally cars are about performance, great traction, great handling...

WRX Stil and EVO are excllent track cars if you can forget about the luxo factor...

Yeah,... I forgot about the Z350 ... another excllent track car that handles like a Porsche...
Sorry, but a 350Z doesn't handle ANYTHING like a Porsche.

Obviously I don't know for sure, but having seen the log manifold on the Renesis, I would wager that there are significant gains that would be possible simply by moving to an equal length header setup. How this would work with the side ports, I'm not sure, but I can guarantee Racing Beat already has a Renesis in their shop and are figuring it out as we speak.

yes, it's true you could probably gain a little bit of torque (for a whole lot more power) up near the redline with a shorter length header... the exhaust header would bolt on directly underneath the intake headers, and might make things a little tightish if you're doing a custom setup with great big flanges (like Racing Beat always does)...

i'm not sure why Mazda would use that "log" style of exhaust header, other than to more easily monitor it (O2 sensors and what have you), and to maybe slow down the velocity for the cat (enhance the reaction)??

the rest of the exhaust system, SEEMS at first glance, to be top-notch... the muffler is obviously going to hold back a little power, but i don't wanna guess how much could be gained by going to a "low backpressure" fart can...

hey Buger, math-wunderkind-and-idol-to-millions, i've got a good 'un for you...

what would the projected bore be of the "16B" RENESIS (hinted at by Dan The Man), supposing Mazda goes up another 10 or 15mm?? stroke is 40mm, as i've posted earlier...

i'll see what i come up with, and we can compare notes :D

buger 'keech and anyone else with rotor knowledge i read this from glenn butcher over on mazdarotaryclub.com:

"The RENESIS Rotor Housing (photo taken by Dan Mazzella) looks very much like it could be adapted to still use the Peripheral Type Exhaust Port.

OR you should be able to take an older style Peripheral Port housing and bolt it into the engine. Therefore having Side Ports and Peripheral Ports. More gas in and out means more power!

This is absolutely brilliant for racing engines! NOT RECOMMENDED FOR STREET USE OF COURSE!"

does this sound actually possible and reasonable?
:o :eek:

heh heh... boogs wanted to have an rpm+throttle sensitive perhipheral port...

but it COULD happen, but not with the Racing Beat style mega-flanges, 'cause they're huge.... or wait, duh, i'm stupid... they'd make one that fits all four of the holes that're comin' out of the engine...
that'd be quite sick, actually... look out SPEED World Challenge!! ;)

hmmm... about that intake side though... how could you increase that without resorting to traditional things like a bridge port??

Originally posted by wakeech
hey Buger, math-wunderkind-and-idol-to-millions, i've got a good 'un for you...

what would the projected bore be of the "16B" RENESIS (hinted at by Dan The Man), supposing Mazda goes up another 10 or 15mm?? stroke is 40mm, as i've posted earlier...

i'll see what i come up with, and we can compare notes :D

Hi Wakeech,

Hmm... I briefly read the thread on the autoweek forum that you mentioned a while back. I was going to post something when you originally mentioned the "oversquare" nature of the rotary but I think there are a lot of things that need to be explained before we can even discuss this.

The first thing would have to do with piston bore/stroke measurements and how it relates to rpms, torque, etc. Bore is the width (diameter) of a piston and stroke is the length that the piston can move up/down. If I understand it correctly, a piston engine with the same bore and stroke measurements would be called "square". Typically, engines with a long strokes and short bores produce more low end torque and don't rev as high. Engines with short strokes and wide bores have less low end torque but tend to rev higher.

If we are comparing rotary and piston engines based on their "squareness", we must know what how squareness affects a piston engine. Theoretically, some people say that the oversquare and undersquare engines should have the same torque characteristics if the displacement is the same. In the real world, a piston engine with a very wide bore and short stroke has more area to have larger valves than one with a short bore and long stroke. Short explanation is that a short bore/long stroke engine can breathe comparatively better at low rpms than high and a wide bore/short stroke engine can breathe comparatively better at high rpms than low. This would explain why the long stroke engines generally have higher low end torque than the short stroke engines. Short stroke engines can also rev much higher than long stroke engines because each revolution of the driveshaft on a piston engine means that a piston goes up and down the length of it's stroke. A short stroke engine has less distance to move so more revs can happen for a given time span.

It is true that you can compare the rotary engine by trying to give it piston measurements like bore and stroke. What I earlier found was that the eccentricity of all recent Mazda rotaries is 15mm (not the 40mm that JustinTX had?). You guys did a good job to figure out the calculations to compare the rotary to the piston however. :)

A piston displacement is measured by looking at the displaced cylinder volume. A cylinder can be thought of as many flat circles that are stacked so that they have height. The volume then can easily be figured out as pi * r^2 (area of a circle) times the height (stroke) of the cylinder.

To figure out the "piston related bore" of 1308cc rotary engine see below:

given: "stroke" = 15mm = 1.5cm
Displaced volume of one rotor is:
stroke * [pi * (bore/2)^2] = 654cm^3
1.5cm * [3.1416 * (bore/2)^2] = 654cm^3
3.1416 * (bore/2)^2 = 436cm^2
(bore/2)^2 = 138.78cm^2
bore/2 = 11.78cm
bore = 23.56cm or 235.6mm
1.3L rotary has a bore of 236mm and a stroke of 15mm?

The above result is even more "oversquare" than your previous calculation! After all of that work however, I don't think the comparisons are meaningful. The rotary and piston engines are very different in certain ways and I don't think that the reasons why an oversquare piston engine can rev high are the same as the reasons why a "oversquare" rotary can.

I think the redline of a rotary is determined by weight of the rotors (lighter weight means less e-shaft flex) and by breathing effectiveness. In the case of the Renesis, I don't think e-shaft flex was the limiting factor in the redline. If breathing effectiveness at high speed was the limiting factor, how can we get more air in at high rpms? Perhaps something I mentioned in an earlier post in this thread? A peripheral induction port/path that opens at high rpms would induce some high speed overlap and aid in volumetric efficiency yes? I'm no mechanical engineer however and Mazda has people that are far smarter than me. Whatever options there are, I'm sure that Mazda is exploring them.

The most obvious way to increase hp/torque would be the first thing mentioned in my original post in this thread. Of course we are hearing the rumblings about a possible 1.5 or 1.6L renesis for future cars. 90mm rotors will give the new engine a displacement of approx 1475mm and 95mm rotors will give the new engine a displacement of approx 1553mm. Hopefully SuperDan will have more info for us about this stuff. :)

Brian

Originally posted by Buger
The first thing would have to do with piston bore/stroke measurements and how it relates to rpms, torque, etc.

The above result is even more "oversquare" than your previous calculation!

I think the redline of a rotary is determined by weight of the rotors (lighter weight means less e-shaft flex) and by breathing effectiveness.

The most obvious way to increase hp/torque would be the first thing mentioned in my original post in this thread. Of course we are hearing the rumblings about a possible 1.5 or 1.6L renesis for future cars. 90mm rotors will give the new engine a displacement of approx 1475mm and 95mm rotors will give the new engine a displacement of approx 1553mm. Hopefully SuperDan will have more info for us about this stuff. :)

Brian

thank you for the timely reply. ;)

sorry to all, for ranting about oversquarness, whilst those not into engine design havin' NO idea what i was talkin' about. uh, let's see....

*sound of 200lbs of man falling over flat on the floor*
MORE oversquare??? :D heh heh heh heh... you're right this ratio doesn't apply to the rotary, mostly because it doesn't operate as a cylinder, but more how an orbiting and rotating "fat triangle"... the output shaft the rotor acts upon travels at a higher rotational speed than the rotor, completing 270 degrees of rotation for one "power stroke", which lasts only 120 of rotor revolution. for reference, piston engines have (piston-to-crankshaft) connection rods which act upon the crank shaft for a (theoretical) maximum of 180 degrees per power stroke. this extra 90 degrees of output shaft rotation (not to mention the rotary's inherent efficiencies with regard to maximizing leverage during the power stroke) must have a large role to play in the magically magnificant torque figures this engine, with a 15mm stroke, can make. i really hope i'm not repeating something that's already been said (on this board...).

shaft flex is something pretty easily overcome, with regards to evolving the engine, and as you said probably isn't the reason the RENESIS starts to choke at 8400 rpm... breathing.
actually, i've been lookin' towards the (horrendously) complicated intake system, which is really quite beautiful, but is really leaning towards the over-complexity of the 13BREW's twin turbo system... ;) that must mean it's fast!!
the large airbox was said (by a member whose name i can't remember, sorry bud) that it created a slow flowing resevoir of air, ready to be sucked up by the engine when one gets on the gas "spiritedly"... so let's ignore inefficiencies in front of that, and let's look to the hind (toward the engine). the triple-path induction runner system is obviously not going to be as efficient at a certain rpm that an uninterrupted, single runner system would be (at the rpm it was specifically tuned for), but does deliver a pancake-esque torque curve.
from the display cut-away engines, i could percieve no difference in the diameter of the runners, but that doesn't mean there isn't any. if, in the instance that it is all the same diameter with the aim of reducing production costs, then when one thinks of the turbulence which would be present in the short runner at WOT operation, a runner of slightly (single digit mm's) larger diameter may increase the efficiency of the runner enough to get another few hundred rpm of useful operation. oh, to explain why this increase in diameter would help with the turbulence, the velocity of the air being inspired reduces (as it's a certain volume of air/min at maximum volumetric efficiency of the engine, and thus it's speed depends upon the area of the oriface it's travelling through), reducing specific momentum, and also the boundary layer (the turbulent layer of air which drags slowly upon the walls of the runner) may be inhibited in its ability to slow down the intake air. let's not also forget that this would hold true for a perfectly straight runner, and that the runner in the RENESIS is contorted... although it's probably not possible to help it, straightening the whole thing out would in fact help a little efficiency-wise.

again, thanks buger for your cool post... these always take me a long time!! i hope yours are all fast (they don't seem to take you much time to type...:))

First off, AWD can have as much oversteer as you want. I can go buy a $150 adjustable rear sway bar that will have me spinning out at every corner.

Also, Audi AWD cars were banned from Touring Car Races after Dominating the everyone else, including BMW. Audi runs FWD now. Does this mean AWD is the ultimate answer? No, just means it sure isn't a mistake!

Now, on to the subject at hand. On the previous engines, the exhaust port Could be widened along with wider rotors to take up the extra exhust. No-one has mentioned that with the side exhaust ports, making the Rotor wider means the exhaust gases get farther from the exhaust port. More of the exhaust stays with the chamber when it cycles around for intake. Isn't this effectively the problem with older engines - Intake/Exhaust overlap? Great for racing maybe, but emissions would drop.

With the old design, the intakes and exhaust could scale with rotor width, while with the side ports the sizes are determined by the fundamental shape of the rotorary. With the side ports there is an optimum comprimise in size/shape for a given rpm range.

Tom

P.S. If you would like a good demonstration of AWD oversteer, the first Rally of the season (Monte Carlo) is coming up this weekend. Speed will have coverage Wednesday and Thursday after.

sorry Tom, but i don't follow you on almost any part of your post regarding the rotary engine... except that recycling partly-combusted exhaust gases (from the cool zones on the rotor) is better for emissions, not worse... :)

the Audi Quattro banning i think had more to do with engine size allowed than the 4 wheel drive, IIRC, but i could be wrong... it's not THAT big an advantage though, especially in road racing.
also, a poorly setup car spinning isn't the same as having oversteer... even FWD cars can spin, but not rear-end oversteer...

oversteer on a loose surface, however, doesn't really count as that's more related to momentum than power-on oversteer...:)

I tend to blurt out my answer without any of the steps I took to get there. Let me use an example for the side versus peripheral port thing - take the RX-8 rotor, and double the width. I know that wouldn't be done in production, but I need an example.

When the rotor width doubles, that means twice as much air needs to get in to take advantage of it. The intake and exhaust ports need have twice as much area to get twice the air in.

To let the engine breathe with all this new found capacity, peripheral ports means the port width can also double, to let the air in. The size of the ports aren't limited when the engine changes size, since the port width can scale right along with the rotor width.

With side ports, the shape of the port is increased to double the cross sectional area (roughly a 40% increase in each dimension). With this new area, the intake port intrudes either into the exhaust part of the cycle, or the compression part of the cycle. The bigger exhaust port would intrude either into the power cycle or intake cycle. That's why I was saying the intake port on the new engine is the best comprimise for the engine. I'd draw something up but I'm at work so I have to look like I'm working. :D

On the emissions, I'm still catching up on rotary design - I switched around some of the problems the old engine had, I think. with the RX-7, all the unburned stuff got scooped out with the periphery port, and I mixed that with carrying it over to the intake cycle. I guess the carryover of exhaust isn't entirely bad, to a point.

As for the sway bar, it affects both lift-of throttle oversteer and power-on throttle oversteer. My car isn't powerfull enough to over come the built-in understeer except in first gear. In rain & snow, this is easy, while on pavement it takes a lot of TLC and doesn't stay long (the limited slip kicks in and trys to steer me straight)

I guess it seems silly to say AWD has no oversteer when the major racing series that actually uses oversteer to a significant degree (World Rally) is dominated by AWD. As I said earlier, check Speed Wednesday and Thursday for coverage of a Paved Road Rally.

For a good video (12megs I think), Try this:
http://www.randyzimmer.com/video/music_videos/wrc-2002.wmv
Set to Linkin Park.

AWD Donuts (3.5megs)
http://www.oman-hp.com/videos/imprezadonuts.mpg

Originally posted by SlideWRX
I guess it seems silly to say AWD has no oversteer when the major racing series that actually uses oversteer to a significant degree (World Rally) is dominated by AWD.

the oversteer in the WRC is, again, from momentum, and not power. i've been into the WRC, and it's tech, for a few years now and really, on the asphalt the only way you get oversteer is when you set the diff to throw all the torque to the rear wheels, effectively makin' it a RWD car (a la Panizzi at last year's Corsica Rally, doin' the big ass doughnut at forget-the-name-of-the-big-hairpin)...
the reason that WRC has been dominated by AWD for the last, what, 20-25 years is because it simply distributes the accelerating force to all four wheels... on a loose surface, that's surely double the amount of available acceleration in comparison to a RWD or FWD only car...
in a road race, however, often there is sufficient grip in the driven wheels that distributing that force more equally about the 4 wheels doesn't garner any significant advantage, and adds all the weight and complexity of the drive system.

anyhoo, back to the RENESIS... i completely understand now, thanks for untangling the web of "sides" "ports" and "perhiperals" you seemed to have weaved in the first post... i really had little idea what you were talkin' about.
thanks.
pertaining to that, i also have the same concerns about the possible 90mm wide rotors that are rumoured to be in a higher powered next model RENESIS... the ratio of port size to combustion chamber volume is down, and it'll be interesting to see how taht problem would be solved... supposing of course they will make wider rotor'd engines :)
then again, as i said earlier, the chokin' of the engine in the mid 8k rpm range may just be from inefficiencies in the induction side runner system, and may have nothing to do with the ports at all... :confused:

Good point about the exhaust port area and increased displacement SlideWRX, the exhaust port size will probably not change very much (if at all) for the proposed 15B.

Even if the exhaust port size does not increase, it should not have much of an impact on a small 10mm increase of the chamber width. Note that the 1.3L renesis already increased the exhaust port area approx 100% over the previous 13Bs and exhaust efficiency is very good.

In the long term future, I don't think Mazda will increase the width too much more. Mazda had already experimented with a 15a (15mm eccentricity, 105mm generating radius, 90mm width) in 1973 so a new 1.5L renesis will not really be breaking new ground in terms of it's dimensions. Mazda was also going to experiment with a 22a (18.2mm eccentricity, 127mm generating radius, 95mm width ? ) but the oil embargo in the early 70s killed both the 15a and planning of the 22a.

It is interesting to see how Mazda changed the intake system on the renesis from 1999 to 2003. The original design in 1999 had 3 seperate intake paths and 3 different dynamic effect lengths. The 2003 design has only 2 seperate intake paths serving the 3 different dynamic effect lengths. The press kit diagram of the intake seems to show at first that the all of the paths are interconnected. Not many people know that they are not. See below comparison of the 1999 and 2003 intakes.

Brian

Buger, I think you're right - the ports are so much better that with a 10-20% change in width it shouldn't matter much. It is probably more a matter of tuning the intake/exhaust manifolds. I think I'd rather see a third lobe, just for the huge increase in power. Considering two lobes make 250 hp, three should make ~375! :) :) :) Aw, heck just go for four lobes!

Tom

(lobes??)

anyhoo, i've got another idea to bring this thread back to the fore: does anyone know how exactly the 5+6th ports on the RENESIS will be actuated??? they'll again probably be (what'd they call them...??) rotational valves again, as they were in the 13B, but how will they be controlled, and by what??
in the previous 13B, they were actuated by a mechanical system which directly applied exhaust back-pressure to two small push-rods, which then rotated the valves (which are like tubes with holes cut in the side to match up with the ports they open) to open the ports... well, alright, i've never seen or touched this system all apart, this is just what i get from 'net readin', so i could be way off...

in ANY case, does anyone know if these extra ports will be operated mechanically, or electronically, governed by the ECU???? that would be pretty neat... :D

If they were electronically control you could change it with maybe a new ecu or switch. That is a good question.

It is interesting that we are hearing rumors of a 300 hp Mazdaspeed RX-8 or next gen RX-7. People are speculating whether the increased hp will come from a supercharger, turbocharger, increased displacement, etc.

We have already heard the rumors of a 10mm increase in rotor width but that alone would not seem to explain a 50 hp increase from the current renesis.

How do guys think Mazda might get the 50 extra hp? :)

Brian

No guesses anybody? It is possible that the compression ratio may go up to 10.3:1 or something. I believe it is pretty common for other makers to take the same engine from their other cars and up the compression for their top of the line performance cars.

Perhaps the reason why the estimated horsepower went down from the RX-Evolv's 280 is that they lowered the compression a little to erase any reliability concerns for their new engine. It is interesting that there was not a single leak about the compression ratios of the evolv or pre-production rx-8s. Hmmm...

Buger,
What they may end up doing is taking some of the linear torque band out, run a different type of intake that is only setup for high rpm running. Seems to me that you could clean up the intake track and add a few horses on the top end. Problem would be you now have a peaky engine but you get a higher horsepower. With this the redline could have been changed and then the gearing raised to give fast times. Compression ratio could also be another option. I believe rotary news said something about there could be some porting that could be done to raise RPM. Maybe a conjunction of many things to get the 300hp. I think they will not FI the engine though. Can't wait to hear the renesis at 10k or even maybe 11k. hehe

I also think that Mazda will probably tune the intake a bit to improve the high rpm breathing. The ports may be a little more aggressive unless the difference is too minor and Mazda wants to bring some costs down by using the same side housings.

If the same width rotors are used, I could see a higher redline if the intake can supply enough air. The increased weight of wider rotors would raise the rotor weight to about the same as the old 9.54 lb ones though so I don't know if the wider renesis will have a higher redline than the current one.

Hmmm... intereting point in here. All, I know Mazda have not done much with their cast/forge re-tooling in their two factory where rotary parts are made to produce an all-side port rotary engine. They have just innovated their current designs due to cost. I assume their bigger displacement 13B/Renesis 2 rotor version of 10mm more per housing, will just increase their cost of producing rotaries. Since now they totally have to make new rotors, housings, eccentric shalf, plates, & R&D.etc.etc. I see this to be stewpit IMHO. I would just use the same concept of the 2 rotor-RENESIS & make a 3 rotor-RENESIS (all-motor). Since most of the tooling are already made, most of the parts are interchangeable & it's already proven that the 3-rotor works good in Japan. If they where to produce a 2 rotor that's bigger 10mm, the cost of R&D will be as much if not more to make a 3-rotor RENESIS.

A (20B) 3-rotor RENESIS w/stainless rotors (like the 2-rotor renesis) will approx. produce easily 355-400Hp@7000rpm all-motor & produce torque of arround 250-300ft.lb.@3000rpm. And, rev up to 8000-8400rpm reliably on stock Cosmo 20B eccentric. If eccentric shaft upgraded to 1 mm dia. like the Mazda 13G, 9000-10000rpm, but I'm not sure if rotor bearings riability will be good due to more component friction. Also, the 3 rotor will have the revolution speed of a 2-rotor, but with the torque of a small-block V8, thus the engine will not beg you to turn off the A/C, & other engine accessories like the 2-rotor. The 3-rotor RENESIS will seriously meet most emission standards, cost in production (the tooling it's already made!), and give the competition some serious performance competition. Since, IMHO I think this would be a worthy replacement for the Rx-7, since the whole concept of Rx-7 with sequential turbo totally failed in the US due to mechanics training & easy tampering of the engine... and now bigger displacement of just 1.4 or 1.5 liter will just be dumb .

sorry amgtortoise, a 3 rotor just ain't happening...
it's easier to leave it 2 rotor, and simply cast wider rotors, and wider rotor housings, with slightly longer e-shafts. it's more a matter of cost than capability: Mazda doesn't need to make a 500 hp rotary motor yet. if/when they do, then they would probably step up to a three rotor.

a thought: what if, now that the EXHAUST ports are on the side, we put the a really big INSPIRATION port on the PERHIPHERAL SIDE as the main port, eh?? then with controllable secondary side ports (or maybe just one)... how about THEM apples, eh??

... i'm just surmising such a thing, as HC leakage mayn't be such a problem with a perhipheral inspiration port (now with the side exhaust ports), as it would have been in the past... i mean, the only reason Mazda moved the intake ports to the side was to try and eliminate as much overlap as possible, but couldn't move the exhaust ports 'cause the apex seals'd coke up without them there... hmmmmmmmm.... *evil laugh*

Originally posted by wakeech

a thought: what if, now that the EXHAUST ports are on the side, we put the a really big INSPIRATION port on the PERHIPHERAL SIDE as the main port, eh?? then with controllable secondary side ports (or maybe just one)... how about THEM apples, eh??

hmmmmmmmm.... *evil laugh*

wait wait wiat ..... say that again?!:confused:

You can buy perhipheral intake port housings from racing beat for the current 12a, or 13b engines, but for street driving they suck, they dont make any power until about 9-12k rpm at which point they become unholy powerful. Of course these housings also have the perhipheral exhaust ports as well, maybe side exhaust, and perhipheral intake would be a different story.

yeah, those're the racing housings...
what i mean is a wide (very wide, with those 90-100mm wide rotors) and not-very-tall perhipheral inspiration port, with auxillary computer controlled side ports... it COULD be positioned (i'm guessing) so that there'd be not too much overlap...

but yes, i am talking about an unholyly (;)) powerful 1.5-1.7L RENESIS... for the next RX-7, eh??

Buger . . . you look like a rotary nut. Congrats and thanks for a great breakdown of the rotary renesis.

Originally posted by wakeech
sorry amgtortoise, a 3 rotor just ain't happening...
it's easier to leave it 2 rotor, and simply cast wider rotors, and wider rotor housings, with slightly longer e-shafts. it's more a matter of cost than capability: Mazda doesn't need to make a 500 hp rotary motor yet. if/when they do, then they would probably step up to a three rotor.

First of all, IMHO it's not easier to make a larger displacement 2 rotor which will involve a completely redesign of a new engine. The R&D cost will be much higher, & why would Mazda manufacturing go for "RE-TOOLING" to produce a larger displacement, the current 13B-RE & 13B RENESIS design tooling have already being PAID for, all they had to do it's to innovate, thus we got the RENESIS. I could only think of multi-rotor (3 rotor or 4 rotor) production as their next step in innovation. And, btw we are lucky for FORD executive allow Mazda to re-introduce the RX-8 Rotary engine. The RX-8 car sales will decide the fate of the rotary, otherwise they will kill the rotary engine.

no, there would be almost no re-engineering necessary. as it stands, they would need only to add 15mm to the middle of the rotor housings, stretch the lobes on the e-shaft by 15mm each, and widen the rotors by that same amount... in all, you're only changing 3 pieces, none of which present a problem in being changed that way... it's been done before, and would be a good solution again.
the engine would then be only about 30mm longer, in reality, with very little in the way of added mass. the few hundred cc's increase in displacement would allow for a pretty big increase in power, and would be a very good candidate for a higher power rotary motor at a very low cost.

with a three rotor, however, you have to come up with new a new intermediate housing (which has two outer gears on it) that can still aspirate two rotors on either side, and a make two peice e-shafts... this adds up to more expensive components, real R+D cost, and a much much bigger engine. really, this is engine is just too expensive as a higher power alternative, not to mention too much engine for a sports car in this price range. would it rock if Mazda did someday again make a 3-rotor motor?? yeah, but i sincerely don't think it would be in their best intrests right now, especially with the considerably cheaper alternative of just making a wider twin rotor.

Originally posted by zoom44


wait wait wiat ..... say that again?!:confused:

whoops!! sorry, okay i'll do it again.

imagine your regular 13B, with a perhipheral exhaust port and side intake ports, but stand on your head.

now the intake is on the perhiphery, with the exhaust ports on the side... the pehiperal intake port would not be of the same shape (not so tall), and further up to try and keep overlap closer to zero... also, this would still allow for controllable side intake ports, which could come in at a certain RPM...

admittedly, this idea of a side-exhaust and side-peripheral intake is an idea that Boogdawg kinda came up with before me, but i'm thinking the ("small" by racing standards) perhipheral port would serve better as the primary port with side ports as the higher rpm auxillaries... of course, this setup would probably lend itself to a high power, rpm motor... something which would go well in an ultra-light next gen RX-7... ;)

ok i get what your saying although i think turning the engine over would have been easier- cause now my head hurts :p