Rotarian_SC

Why exactly would they need to go back to the drawing board and build a new engine? This engine has the strongest internals of any production rotary engine, stronger than the FD internals. And if they did redesign the engine all they would need is lower compressions rotors (which I believe just involves a little calculus, because on a side note i remember my son showed me a problem he had in high school calculus that involved finding the compression on a 13B based on the curve of the rotor or something, I have forgotten the calculus needed) and even if it needed more than just some calculus, it isn't like they have to redesign the housing, or the ports to a large extent. I would favor OEM the same rotors on the Renesis because:

More off boost power
Smaller turbo, so it spools quicker
Less boost needed, less stress on the internals

The lower compression is only needed for high power, when you can't gain power by adding more boost, and I would personally not be modifying the engine to that extent.

Wow, I think RG and I need to have a competition for the longest post

rotarygod

Here's a very simple solution for Mazda that is reliable. Change ONLY the rotors to lower compression ones and retune the ecu. Add forced induction in moderation. Simple isn't it! How would that be going back to the drawing board?

rx8 dx

You would think that Mazda have a group of highly knowledgeable builders and designers, but from what I can see: In this forum there is much more talent (Rotary engine dynamics) than overseas. They should have consulted with the rotorheads here in the USA while there were working on the RX8 project. Maybe that way, at this time we would have been enjoying a super engine.

PhineasFellOff

Can someone make rx8 dx stop posting? Or at least send him to the Lounge section. I think he may be a junior high student.

Rotarian_SC

Agreed on that one. Does he think that he should have been consulted to build the Renesis, because he seems to be making these claims like it can't take boost because I guess he thinks he is knowledgeable about the Renesis. I would have to say I would go with RG over him, as would many on this forum I hope.

Gomez

There's been a lot of figures, facts, and fiction in this thread.....but the one undeniable fact is that Columbo was not an adventurer. He was a dude in a trenchcoat with a dicky eye.

Factually Yours, Gomez.

:D

T-von

I say that Mazda should build a NA 3 rotor Renesis w/aluminum side plates to reduce weight. Overall the car would probably cost as much as a FI 13b and have a ton more low end. Mazda could easily sell a ton of these higher powered 3 rotors because not everyone has confidence in the reliability of a FI rotary. I know I would easily pay thousands more to have that engine in my car.

cortc

Time will tell...

Rotarian_SC

I don't think Mazda will do a 3 rotor, that would basically reverse the changes and advances to the Renesis, and I think it would be more likely for them to just increase housing size than add a smaller third rotor in the middle because then there are new balancing problems, etc

NAVILESRX8

iTrader: (1)

Can I get a stronger drivetrain before we start worrying about more power? HAHA...All I really want or need would be the 25-35 horsepower that the CZ gives, but from the factory....that's all. I would like to see a higher performance rotary in what it really belongs in.......a 2 seat coupe.....you don't have to call it the RX7. I don't care what they call it....

Jerico

FI will reduce the overall lifespan of ANY engine. Rotory or not. Unless of course its your grandma driving it and the turbo never has a chance to spool up. Nonetheless FI is more maintenance and more $$ on any engine, in any car. It has nothing to do with the fact that theres triangular thingies spinning around in there.

Maybe Kerry will win the election too. It all boils down to one basic, simple common denominator. Every car manufacturer around the world that exists and once did exist spends loads of money on R&D for piston engines, and has been doing so since people started calling the horseless carriage a "car" for short. The rotory has never seen this sort of attention and thus it'll take more time and more money to find the sort of common knowledge about things like emissions, fuel economy, and FI that there is with bangers. When you really look at the big picture you wonder how it could ever possibly be economically viable for Mazda to pursue such a thing like the RX-8 to begin with. But then to go redesigning the whole engine for some extra weight under the hood, a unique wooshing sound and 50 extra ponies? I just don't see it... Its those kinds of aspirations that can bring a auto manufacturer to its knees. DeLorean anyone?

nucleus

You really don't know what you are talking about! If Mazda didn't want to spend the buck on retooling for the intermediate housing and eccentric shaft we would have an engine that was 3 inches longer and it would have full size exhaust ports in the intermediate housing. Same thing could be done with a three rotor.

Rotarian_SC

This is what I was responding to, sorry about not giving the quote before. If Mazda was going to increase displacement, they would not use a thinner middle rotor, because they could just achieve the same thing by using wider rotors in a two rotor. Also I would be willing to bet that the more powerful engine is not a 3 rotor. 3 rotors weigh a lot, the old 20B weighs double the 13B, because there are lots of balancing issues to be worked out. If Mazda wants an engine that can produce 325hp or so, why would they choose a 650lb 3 rotor engine, a >500lb two rotor, or a >400lb turbo two rotor? I the less just so my numbers don't look conservative, but is the increased displacement in a Renesis going to account for 200lb more, or will a turbo add a 100lb to a Renesis, I think they will each add much less weight that that, and the 20B weighed over 700lbs, so that is at least a 250lb and 150lb weight difference for the 1.6L (I've heard 1.5L as well) and turbo engines compared with a 3 rotor.

I agree with you there, except as far as I know Mazda had trouble building aluminum rotaries that could last, but this is the only way I can see Mazda building a 3 rotor, if it is made out of Al.

Japan8

Are you sure? Everything I've read says an electric assissted turbo for the Renesis... not for the RX-8. Could this be the new RX-7 engine?

Japan8

Well said! This is exactly why I don't want Mazda to FI the 8, and I have doubts about an FI version appearing. Once you combine this with the thought that they may be planning a more hard core 2 seat rotary... there a realy serious question of where is this care going to fit in the lineup?

T-von

Your 20b weight calculations are off a bit. 20b's don't weigh that much(550lbs max with all accessories in turbo charged form). Its the accessories(turbos & manifold, center plate extra rotor ect) that really increase the weight. If a "factory" style turbo is added to the 13b Renesis, I'm pretty sure the overall engine compartment weight will increase nearly 100lbs(turbos,cast iron manifold, plumbing, IC, ect). A 20b short block weighs about 100lbs more than a 13b. So if you compare a FI 13b Renesis to a NA 20b, you would come pretty close to the same weight under the engine compartment. Also if 20b is build with aluminum side plates, the weigh would be further decreased. Mazda can easily do this, it just won't ever happen.

Rotarian_SC

Well I did do a search and about all the websites I found stated a 350kg weight for the dressed Cosmo 20B.

MrRogers

..these guys seem to be.

http://www.pettitracing.com/wp-conte...lureTheory.pdf

i am very interested in turboing my 8. ive spent easily twelve hours reading on the subject. i plan to purchase a second motor and port it correctly before i put a turbo together.

Brettus

iTrader: (2)

Nice thread bump .
What you probably don't know is that the Petitt 'failure theory' was formed from seeing what happened when the OMP was disconnected and the cars were run on premix .
That failure mode does not happen on street driven turbo renesis engines that retain the OMP. Whether the same thing happens on turbo renesis race engines that do retain the omp is not confirmed however.

Karack

those engines were also probably run hard and on the track for extended periods of time while in boost where the engine related issues would be most prevalent. like Brettus said, on a street driven car you likely won't ever need to worry about the heat.

backpressure has always been an uphill battle with the rotary engine, you can see any seal skip over an open port that generates pressure: lead/trail spark plug ports and exhaust ports. being that the side seals absorb heat quickly but also disperse it quickly puts them at risk in the renesis engines with a turbo that see high temperatures and boost for shorter lengths of time between boost again(internal cooling).

when a critical area inside the engine absorbs too much heat and only has a second or 2 to cool back to normal temperature you usually won't get the desired result no matter what you do.

the reason the early engines could handle boost was because the apex seal absorbed the heat and lifted over the exhaust port, except the much thicker seals could handle the abuse.

so what makes the difference for reliability in non street driven turbo rotaries? periperal exhaust ports.

Brettus

iTrader: (2)

Sounds plausible .............. but do you know for sure ?

Karack

i don't think anyone will ever know for sure, but the kicker is that the side seals are usually first to go with a turbo renesis and the reason why is fairly obvious. the 7 engines could handle whatever boost until you detonated and spit an apex seal due to engine tuning limitations. the 10:1 compression would play a large role in that as well but the failure modes seem fairly straightforward.

i'd be rather curious to see a turbo 8 stock configured engine on the track at 10PSI+ and what the result would be, i'd put a bet on the side seals burning up within a session or 2, maybe quicker.

skc

Mazda Australia did produce a turbo RX8 and competed in the Targa Tasmania race. The engine performed well. Ric Shaw racing purchased the car and has run several races without issues.

The engine had race seals, ceramic bearings amongst other engine upgrades. Power figures was not quoted however we believe it is around 400hp. The car chewed up the gearbox in its first run due to the power upgrade.

TeamRX8

iTrader: (25)

What street driven turbo Renesis engines are running 400+ Whp???

Brettus

iTrader: (2)

The Diaso race cars ran mid to late 300s which is , coincidentally, only marginally more than what mine and
Slash's are running .