I've seen a few comments suggesting that Mazda will supercharge or turbocharge the Renesis to increase horspower, and, of course, low end torque. I've gone on record saying that the car needs more torque, but I do NOT want to see a forced induction rotary again and would never buy one. I'd rather have a NA Renesis with less torque than a turbocharged/supercharged rotary.

Remember all the problems with previous FI rotaries? Have we forgotten already? The well-deserved reputation for poor reliabilty, durability, and usually driveability? Once the extra air is inside the engine, it does not know if it got there via a supercharger or a turbocharger. No matter how it got there, it's more air, more oxygen, and more pressure. Supercharging the engine is no more the answer than turbocharging it again. I hope Mazda has learned from its mistakes.

Forced induction is not the answer- more, or bigger rotors are. Or perhaps three rotors that are narrower than the current ones, perhaps 1.5 liters in total displacement three rotor vs. 1.3 liter two rotor.

I like low-end torque but I also think the way for the car to keep its character is to keep it normally aspirated. Mazda will find a way to wring a few more ponies and pounds-feet out of it, I'm sure. This is just the first time around.

 

Amen

 

we certainly haven't forgotten that the turbo systems on previous Mazda wankels have adverstly effected the engines durability and cost, but i wouldn't say driveability...

sadly though, we aren't the ones making the decisions; but, i am confident that Mazda will see that all out performance at the cost of anything isn't what most people want, and will certainly factor in the life of the engine no matter how the increase in performance is garnered.

but, as a footnote, i have no idea where people are getting the idea that the RENESIS will be supercharged: in only the Millercycle Millenia have i heard of supercharged Mazdas, and i still have very serious doubts about an rpm-dependant compression system on such a high rpm motor, in an application where people will expect very flat, broad, and simple driving dynamics regardless of the rpm.
... i know some people, and they know some things, and i've heard nothing about this supercharging what not, other than that one article which claims to have insider info, and Dan+Bern's tip from the Mazda engineer about it being built to "take boost"...
wider rotors it seems the most likely to be.

 

I'm with you 100 percent on the "please don't force induce my Renesis" argument. I too want to have my car for a long time.

I prefer three Rotors as a first option and secondly, two bigger rotors.

And, keep the 6 speed manual also.

 

Forced Induction done right is not going to be terribly detrimental to the life of the rotary. From what I understand the 3rd gen suffered from major overheating problems. This coupled with the sequential turbo charger caused major problems. Most 3rd gens are also modified and running one bar of boost, while not necessarily running with correctly tuned ecu. That has to be hard on any engine. What's to say that running a low boost turbo or supercharger would cause to many problems. I am all for boost. I have a really hard time seeing anything for the renesis in the neighborhood of a 3 rotor coming out. And the engineering for such, will be a feat in itself. I bet we will see the wider rotors though. As to the supercharger everyone is talking about there was an article where Mazda mentioned this was something they were working on. Hell if I can find it though

 

I'm hoping power to be gained with the the Renesis is done without boosting also, mainly for the sake of simplicity. I always thought, IF it does get boosted, my preference would be to go with a supercharger, but wakeech brings up a possible good point about rpm dependence. However, I thought a directly connected compressor may be more likely to supplement the bottom-end and midrange of the motor. I know most turbos seem to provide meaningful boost only when the rpm's are up, and the throttle is wide open. (although I heard Volkswagens tend to have little turbo lag)

I would like to see a 3-rotor based on the same internal dimensions as the 13B, in the new RX-7. (at least as an option) Such an engine could be easier to produce, using existing tooling, and would have the advantage of even smoother running due to the counterbalancing effect of the rotor timing of 3 rotors. Has anyone else thought wider rotors, and therefore, a longer eccentric shaft, could lead to more flexing, causing problems at higher rpm's? (yeah, I know, I suppose shaft and bearing diameters could be increased)

 

actually, as far as the E-shaft goes, usually, a longer shaft can handle MORE torque, because the twisting force is applied to the metal spread out over the longer span. Whether this extra torque handling capability will outweigh the extra torque applied by the larger displacement, I can't say, but trust me when I say that the longer the shaft, the better the torque handling capabilities. (I deal with shafts that handle over 1.5 million ft-lbs) but trust me, it isn't in a car..

 

I could see your point about a longer shaft handling more "twist", but a longer shaft supported at both ends would have a longer unsupported area, which would allow more movement perpendicular to the shaft at that area, wouldn't it? I'm thinking in terms of the forces the rotors place on the eccentric shaft to cause it to rotate, throughout their "stroke" in the chamber.

 

So, you're in the **** industry?

:D

 

It is a crying shame that I was beaten to that punch line. Life must go on however. Back to the topic at hand. Personally, I would be absolutely thrilled to see a three rotor engine in the near future. Although I would be just as happy to see a return of the twin turbo system of the 3rd gen. I was under the impression that most of the reliability problems from this system came from either a lack of cooling, or a poorly managed engine. Both of which could be addressed with a little tlc from mazda's engineers.

 

Have you forgotten that unmodified FC turbos lasted as long as other factory turbo cars of the time? Have you forgotten that the reliability issues with the FD engines was not because it was turbocharged, but in how it was designed and implemented? Mazda's error with the FD was not with the fact that they turbo-ed the car, but with the fact that they tried to make a complex system work for too little money. As a friend of mine says "They tried to make a $50k car for $30k". And to get to that price point, they ended up sacrificing reliability and longevity.

If they don't make that same mistake with the next forced induction car, then things shouldn't be so bad.

---jps

 

Right on brother! The FD's enemy was heat, pure and simple. In fact, the J-Spec FD's front nose was redesigned to make for better airflow and numerous changes were made under the hood to improve longevity. The 2003 model FD had even more power and torque than the last US-Spec model and was more reliable to boot. If Mazda introduces forced induction into the RX-8, it will most likely be in a single turbo configuration, which is has been a rock solid design for Mazda in the past.

I think that a forced induction model could be built to be easier on gas than a bigger motor would, plus give the benefits of extra power.

 

See, this is where my inexperience with rotaries comes in to play. (I'm just an engineering guy) Does the E-Shaft have a bearing between rotor housings? or is it supported only on the ends?
if it is supported in the center, than this will absorb the extra lateral forces. If not, than yes, these extra forces could be a concern with the longer shaft and flexing forces. Ideally a shaft like this should have a center bearing, but like I said, I'm a little new to rotaries.

Edit: Keep in mind, that it would take a LOT of extra forces to cause a problem, and if you are already talking about building a new longer E-shaft, you ought to be designing in the exta strength needed.

 

Yeah, the e-shaft on the two-rotor engine is unsupported in the middle, only front and rear mains. They can use a one-piece center housing then, and still assemble/disassemble the engine. (see link) http://www.rx-8.mazda.co.jp/products/driving10.html

The 3-rotor has a two piece shaft with a tapered (I think) coupling, with an extra bearing between the front and center, or rear and center rotors. (I don't remember which it is)

 

You know I would trust you but you are wrong. If you are an engineer you better review your sophomore strength of materials class. A longer shaft of the same cross sectional properties cannot handle more torque. Does this little equation ring a bell?

Torque = [(Max Allowable Shear Stress) X (Polar Moment of Inertia)] / Shaft Radius

The only difference in regards to torque for two shafts of equal sectional propoerties but differing lengths is angle of twist.

 

Not only reliabilty is a problem with forced induction but the extra costs associated with it. Do we want to the Japanese manufacturers prices themselves out of the market again like they did in the mid 90s with all those expensive turbo cars (Supra T, 300ZX TT, RX-7)?

I think the RX-8 packaged just about right now with a decent amount of HP, styling, tech and cost. Looks like Nissan doesn't want to make the same mistake also with their non turbo 350Z.

 

Heat is the main problem for turbo FI autos in general, and faulty boost timing coupled with an inadequate cooling design in the 7's rotary block (inadequate for turbo apps anyway) created a disaster waiting to happen. My understanding is that the repositioning and resizing of ports within the Renesis was brought about partly because of the previous problems associated with OEM FI models with the idea being to dissipate more heat. while the porting for the 6MT RX-8 looks pretty involved as far as connecting any FI system, I'm fairly confident it will be done eventually. Posi pressure Eaton Roots style (NOT centrifugal) S/C applications should provide some good gains in low and midrange HP and torque. I think the draw toward superchargers is a direct result of the heating problem (turbos share engine oil, so if it isn't setup right you're basically screwed across the board) since S/C systems are generally self-contained and retain far less heat. The pressure concern is noted, but the general consensus is that the block will take a ten pound boost, which should be more than adequate for anyone who still wants to use this car on the open road. Doubt we'll ever see a twin turbo application again given the advances in singles, and though that whine and growl as it spools up is satisfying...so is blowing by the guy who's turbo is still winding up:D once we realize the potential the 8 has, 911s best beware

 

What about all the blown apex seals? Surely extra pressure in the chamber had something to do with those...

It will be interesting to see what happens in the future with the Renesis. I still like the idea of bigger, or more rotors. Could Mazda make a 3-rotor with narower rotors, so it has the same physical dimensions as the current 1.3L Renesis?

 

I would imageine the blown seals have more to do with the engine overheating causing than with the pressure. The seals see a LOT of friction, and I would imagine they are probably the hottest part of the engine.

 

And the 3000GT VR4, MR2... While FI engines don't normally last as long as a NA engines, alot of the apex seal problems on FI rotaries were caused by excessive pre-detonation. It's all in the tuning...

---jps

 

i originally thought this was thread was about no one force inducing their engine, but i'll have to agree w/ the majority of you guys out there, i don't think mazda should sell the renesis force induced...but just leave it to the owners to take it upon themselves =)

 

Is that what the majority thinks? Not according to this poll:

http://www.rx8forum.com/showthread.php?s=&threadid=3189

At the moment I write this post, there are twice as many people who think Mazda should offer a forced induction version of the Renesis as there are people who think Mazda shouldn't.

Is this poll accurate? Or have the nay sayers just declined to vote up to this point in time? The only way we'll know for sure is if everybody votes.

And before you ask: Yes, this was a thinly disguised plug to encourage more people to vote in my poll :D

 

Blown apex seals are usually due to detenation, which is caused by improper tuning (too lean). There are a large number of heavily modified TIIs and FDs that are running a LOT more boost than stock, the last a long long time (when they're properly tuned). Many people even daily drive them.

 

Blown apex seals are usually due to detenation, which is caused by improper tuning (too lean). There are a large number of heavily modified TIIs and FDs that are running a LOT more boost than stock, the last a long long time (when they're properly tuned). Many people even daily drive them...from M477's post

that is exactly why seals were destroyed. many people just threw the usual intake/ catback exhaust combo and forgot to upgrade the fuel system and engine management. i know some that had an engine rebuild and got the 3mm seals to safe guard against detonation, but eventually a new engine would be needed because their fuel delivery was inadequate. no matter how thick the seals are, proper tuning is what protects the engine.
obviously, allowing the engine to breathe more freely will increase boost, leading to lean conditions. as a "rule", more than 2 mods will require upgrading the fuel system.

also, letting the car sit for long periods of time led to deterioration in the apex seals. even if you can't drive the car, let it idle in the garage for fifteen minutes once a week, and your rotary engine will last a while.

don't ask me how i know this.

 

You took the words right out of my mouth. This pretty much sums it up ... rotary turbo's can be reliable. But it's the rats nest of vacuum hoses, solenoids, and actuators that isn't