zoom44

fred has been known to say that from time to time. so the formula for figuring out volume is

Excentricity X Radius X Width X 5.196. then multiply by the number of rotors. found it here http://66.102.7.104/search?q=cache:h...ient=firefox-a and here http://www.rotaryaviation.com/rotaryhistory.htm

E x R x W x 5.196 = 750cc . so lets plucg in some numbers and see what we can find out. lets keep the W the same as current and solve for E and R. what is the current W?

globi

I agree that it makes more sense to add a supercharger (be it turbo, mechanical or whatever) on the current engine than designing a new engine that is slightly larger and I'd be also very surpised if they came up with some 15B.
But even if you can't increase the port area you can still increase the power of the engine. If you increase the stroke on a piston engine you increase power over the whole rpm range even though the valves didn't increase in size either. Admittably, the power gain is higher in the lower than in the upper rpm range.

rotary crazy

the thin is that mazda prefers NA (as do I) and the logic for going bigger is the same that was used to go from 12a to 13b and remember that the 12a turbo made the same power that the 13b NA.

If mazda wants to keep up with the competition they must find a way to increase power and TORQUE in NA form and if you look at the competitors they all increase power by increasing displacement.

what way is mazda going to use? we'll see and have fum guessing

but there are 2 ways of doing it 1 increase the rotor wid( more easy and faster) 2 increase the entire engine wid and height, entire new engine, more heavy but a lot more power

rx8wannahave

3 rotors anyone....

Allow me:

rotary crazy

I sugested 3 rotors as the best solution but most people here think is too expensive for the rx-8.

rotarygod

This is true. If there was more power from a 1.5, this gives us some different possibilities. If in fact a larger 1.5L Renesis with the same port size does in fact make more power due to added intake velocity, this would also imply that the current Renesis has ports that are too large and it is not making the power that it could be. In which case you could get more power yet out of this engine and therefore have no need to go larger. You also need to remember that the current engine brings more intake ports and area online as rpm's rise because they are maxing them out. This doesn't imply there is much room left in area to get much more power.

We can't really compare the old 10A, 12A, 13B ,15A, engines to the Renesis and it's scale. Remember that all of those old engines, including the 15A, had smaller intake ports than the current engine. They could very easily vary their size to make some larger than others back then as they had room to grow. There is no more room to grow. Also remember that with a peripheral exhaust port a wider rotor housing also allowed a larger exhaust port while being able to keep the same port timing. With the side ports, we can not add exhaust port area. We are out of room.

It has been said that there won't be a 3 rotor (even though we've had one before) due to added costs and complexity. Dont' foprget the complex nightmare that twin turbos were also that they also used instead of cheaper simpler singles. It is also unlikely there will be a larger 2 rotor due to lack of airflow capability and the fact that mileage will suffer. Don't bring DI into this as a justification. It's not a solution to making an engine larger although it does have it's benefits. What is most likely is that we will see the current size stay right where it is but using forced induction. We will probably also see it progress into the realm of DI to improve other areas. I just don't see a larger engine that makes no more power that uses DI to just bring it back to the current engine emissions and mileage numbers being a practical thing to do. It would make more sense to improve what we have and then to boost it. That would be the cheapest alternative.

It is interesting to note that Mazda has progressed from an 8A and smaller (testing only) to a 10A to a 12A to a 13B and then tried the 15A and 21A configurations but still settled on the 13B size. Use the gas crisis as an excuse all you want but it is this size that had the fewest compromises. It was also this size that was used to add a rotor for the 20B rather than just making a larger 2 rotor. The Renesis castings are all new from the 13B and share nothing. It wouldn't have been any more difficult to make a 15A sized engine if it was so advantageous. All the castings changed anyways. As I've said, I'd be more than happy to see a 1.5L 2 rotor appear. I won't complain. It just doesn't make much sense and the appearance of one would hint of potential improvements that should be made to the current engine.

zoom44

this one was started by wheels magazine.

the original rumour was started by mazda engineers. follow the link in the 2nd post by buger in this thread from 2002
https://www.rx8club.com/showthread.p...t=widen+rotors

edit- oops the link doesnt take you to the article anymore, s'okay as buger quotes the important part.

Aoshi Shinomori

Interesting write-up, thanks for the info

Something that I didn't know and think I know now; the 20b was actually ~1950ccs? I never really thought about it, but it should be just around the 1950-1960 range if it's just another rotor from the 13b, correct?

globi

Actually there would be a way to increase the port area on a 15B. Granted that this would increase complexity, but they could add peripheral ports in addition to the side ports.
Of course the peripheral ports should then only open above a certain rpm (e.g. 6500rpm), to keep the benefits of the side ports.
Also, a widened 15B could still reach the rpm of a 13B.

rotarygod

We are never going to see a peripheral port added in due to emissions reasons so that isn't a viable option. There is no way to get more port area. Even that porting style was tried back in the 70's.

rotarygod

The 20B is just another rotor of the same size added on.

Aoshi Shinomori

And each rotor roughly covers about 654 ccs, when talking about this particular engine, correct? You learn something new everyday

globi

Actually if the peripheral ports are only "add-ons" you can place them very far apart such that overlap is reduced.
Besides if the peripherals only open at a very high rpm, it won't cause emission problems because the drive cycle doesn't require the engine to go up to 8000 rpm or something.

Japan8

RG... what do you think of the use of hybrid over FI? You can loose some weight as you no longer need several conventional drivetrain parts. The electric motor would give the car the needed low-end boost it needs while also improving fuel economy. We can see they are at least studying it with the Premacy/Mazda5 RE Hybrid.

Speaking of which... what do you think of Mazda "re-engineering" the RE to fit transverse mounted in the Premacy/Mazda5 RE Hybrid? Mazda planning other applications?

globi

This is all speculation but for following reasons I believe it would make more sense to 'widen' the 13B to a 15B than to make a 3 rotor 10A:

* The 2 rotor is already perfectly balanced (so what's the point?).
* The 3 rotor is obviously more complex and therefore more costly (33% more intakes, 33% more headers, 33% more injectors, 33% more valves, 33% more rotors, 33% more seales etc.).
* The 3 rotor will be heavier.
* The 3 rotor would have 33% more sealing surface (= more frictional losses and more pressure loss since no seal is perfect).
* The 3 rotor has a higher overall surface to volume ration (= more heatloss = less efficient and less power.)
* If the 3 rotor has 2 spark plugs per chamber the 2 rotor can have 3 spark plugs per chamber.
* The 3 rotor in this configuration (10A) wouldn't allow higher rpms without overstressing the crankshaft. If the rotors were wider and smaller in diameter then there might be a point in making 3 rotors (higher rpm = more power). But would general customers want to buy a car that needs to be run at 11000 rpm to get somewhere?

Why did Mazda built a 20B? Maybe because it wouldn't have gained enough power by widening the 13B or maybe for the same reason it built a 1.8l V6?

zoom44

.

rotarygod

Not true. You have 2 counterweights. One front, one rear and they both weight different amounts. Yes a 3 rotor still has 2 counterweights so this really changes nothing.

Actually it's 50% more which is still less than any piston engine in terms of total number of needed parts. Valves??? They've obviously done it before and put it into production which is more than can be said for a larger 2 rotor.

And? Not much if done right as the rotors and housings would each be smaller. A wider 2 rotor would also be heavier than the current engine. Not much advantage either way.

Again it's actually 50%. It would also have the potential for more breathing ability over the current engine which a 2 rotor wouldn't have. A 3 rotor Renesis of any size can always have 50% more breathing ability than a 2 rotor Renesis of any size in terms of port area. A larger 2 rotor would also have more stress per seal as each seal is responsible for a larger area. A seal that has less stress on it also needs less spring pressure against it (this is assuming a 1.5L 2 rotor vs a 1.5L 3 rotor) which would actually result in a seal that would last longer and housings that wouldn't wear out as fast. [/QUOTE]

Since a 3 rotor could actually breathe better and a larger 2 rotor couldn't, you can't really claim less power and less efficiency from a 3 rotor. You've got it completely backwards. The positive far outweighs the negative in this regards as the negative has a miniscule impact in the first place. The internal surface to volume ratio is an advantage to a smaller chamber based 3 rotor in terms of combustion and fuel distribution. [/QUOTE]

I don't even understand where you are coming from with this one. What makes you think that there is any reason why a 2 rotor can use 3 plugs per chamber and a 3 rotor can't. How does the amount of rotors affect this?

First off, why would you need to rev a 3 rotor higher? Second even if you wanted to (but it's pointless) a 3 rotor could potentially allow higher rpm's than a larger 2 rotor could. One obvious reason which I have already stated is that it could breathe enough to matter up here. There is really no reason to rev higher than the current limit. A larger 2 rotor could not even rev as high as the current engine could for this very reason. The second reason is that a 3 rotor has more eccentric shaft support due to an added bearing. A longer eccentric shaft for a 2 rotor is a longer distance between bearings which is far more stress on the shaft at higher rpm's. This would cause the shaft to flex. It already does at high rpm's to some extent. Making the rotors wider would worsen this effect. A skinnier rotor puts less stress on the shaft due to distances from each bearing. 50% more bearing area for the same displacement would be a good thing. Less stress on components goes back to more reliability. Customers wouldn't want an engine that needs to be revved to 11000 rpm but there is no need to rev one this high as I've already stated so that is a moot point anyways.

Maybe! Maybe because a 3 rotor made more sense than a larger 2 rotor for all of the above reasons! I don't speak of archaic piston engines!

rotarygod

I just went back and read Buger's comments. Here's the relevant part.

If you notice, all Mazda engineers have stated according to a magazine (we know how reliable magazines are about speculation) is that they are looking at ways to increase the capacity. It was Buger himself and not Mazda engineers who made the connection that Mazda has widened rotors in the past. Already stated how this was actually advantageous with a peripheral exhaust port as you actually could get increased port area. He also goes on to show how a multi rotor makes more sense from a performance standpoint.

I do have to point out that if they have ruled out the chance of turbocharging the Renesis, how come Mazda keeps playing with forced induction on the Renesis? I'm not sure I put any trust in a magazine article that has never been substantiated especially one that is 3 years old and came out before the RX-8 even did. I've seen alot of magazines post pictures of the "new RX-7" too and they've all looked different. Not sure I trust them either.

rotary crazy

RG, in your opinion can mazda make a 3 rotor power rx-8 for less than $30,000? a performance version mazdaspeed, lihtter, better handling, 300 NA hp, no accesorys like the evos used to be .

I read some where that mazda was making 20b crate motors for racing teams is this true?

I heard from a very relible source that mazda was testing a lot of diferent comfigurations of rotary engines, 3 rotors, wider rotors, turbo and super charge, hybrids, etc. And the teams that where wining where the 3 rotor the wider rotors and the hybrids, turbo and super charge had relaiblity concerns but this is just a RUMOR .

rx8wannahave

Yeah, RG...it seems your a 3-rotor guy (like myself while I know little about rotary engines).

So, the E-Shaft has to be bigger but from the looks of one rotor housing it seems that the difference wont be that much.

So what's keeping the 3-rotor from becoming the norm? Maybe Mazda should make it slightly smaller (1L) add a rotor to make it a 3-rotor engine and then use direct injection to help with the fuel economy. Also, since it would have more power and torque they then could re-do our tranny to have a higher top end so in reality fuel economy might actually get better and not worse.

But, I don't know much about this stuff. From what I hear from the members here going with a Turbo or SC might just make things worse and I think it's time that the rotary engine starts producing more HP as a NA engine if it wants to gain more acceptance in the car world.

Listen up Mazda...give us a 3-rotor 1L rotary engine making about 325HP along with direct injection and a higher 6th gear and we might just have solved all our complaints in one engine design.

I'm such a dreamer...I know...lol

rotary crazy

And sell the renesis 3 rotor as a crate motor, mazda could sell 10,000 engines.

A lot of RX-7 and RX-8 will fit this engine to they'r cars

zoom44

of course i noticed i knew exactly what he wrote when i posted it i like argueing in circles it keeps people on their toes.

to sum up for those that dont read the link- it was Buger that started the wider rotors rumour 3 years ago but even he was against the idea and pointed out the reasons why a 3 rotor would be more advantageous. later in the thread its wakeech who champions the 1.5 or .6 2rotor. its amazing to me how the conversations repeat themselves with new players

globi

Yes of course it's 50%. 50% more parts is even more money. Of course it has valves or how can it open different inlet ports. (I'm obviously no talking about poppet valves.)

Actually a 3 rotor obviously needs 2 more walls. Which makes the engine longer and heavier.

Yes it's 50% and therefore even worse. It's only the apex seal that needs a higher spring pressure. The side seals are the same and deal with the same pressure.
As I mentioned before you could always add peripheral ports in addition to the side ports if side port area was indeed a problem. However is port area really an issue and is it not port timing? The S2000 has smaller sized valves than the Renesis has side ports relative to its engine size and can still spin as high and generate even more power (breath).

Especially heat losses are obviously substantial in a rotary engine and they are mainly based on the much worse surface to volume ratio of the rotary engine (hot gases cool and therefore lose pressure) compared to a piston engine. And as I said before more seals lead to more 'blow-by' (= pressure loss = less torque). So one should try to reduce that inherent disadvantage and not make it worse by increasing the surface to volume ratio.
With a smaller volume you can achieve better fuel distribution, but if fuel distribution was indeed and still that bad it would have a hard time with emissions in the first place.
Also, frictional losses are almost 50% higher in a 3 rotor 10A vs. a 2 rotor 15A.


Of course it can, it just costs 50% more.

If an engine has higher heat and frictional losses and more 'blow-by' it produces less torque and is less efficient at a given rpm. In order to offset this you need to increase rpm.
This has been known with piston engines and I don't see why this would not be applyable to rotary engines at all.

rotarygod

I still don't buy any of that.

A rotary engine HAS NO VALVES!!!!! None. How else do the intake ports open? It's called the movement of the rotor itself past the port. There are no valves. No poppet valves or anything.

rotary crazy

all of the losses in a 3 rotor are ofset by the increase power, a 3 rotor renesis will produce more power than a 15l or 16l, MPG is another cuestion but theres a lot of people runing aroun with stock port 20b in NA form getting 250+ rwhp and about the same 12 to 15 mpg the renesis gets, theres even a couple of members in this forum with street ports 20b NA getting 320 + rwhp and this all its done on older tecnology.

the thing is that a renesis 20B does not need the gearing to be so agresive so maybe 3.90 instead of the 4.44 the rx-8 has now, or keep the 4.44 but put taller 5ht and 6ht gears.

the sheap solution in the short run are FI systems but if mazda wants to invest in the rotary future the 3 rotor or wider engine and the hybred's must be adopted.