RX7 motors in RX8
 

I was just wondering why every time you see a race rx8 (drift, time attack, touge, tec.) it had an rx7 motor in it or in extreme drag cases a 20b. I know the 13b has a long track record, but is there something that is wrong with the renesis so people don't want to use it?

my opinion/guess ... and this may sound strange to some ... is probably reliability. i have my own thoughts on comparative reliability between the older 13Bs and these new 13Bs, but that's for another time and thread.

my thinking here is that the Renesis is pretty close to maximum performance in stock form, whereas the older engines have a lot more potential and versatility. obviously people have turbocharged Renesis engines, some have experimented with different porting configurations - and some even make impressive power with their chosen changes, but i don't know how many of them regularly race on a serious level. given the extreme conditions of the events you mentioned, i suspect reliability would be a serious issue and i feel the older engines are just a safer decision.

Three years ago, I attended The Mitty at Road Atlanta. A representative from Mazda gave a presentation on Mazda's racing efforts. I asked why the 20B was in the race RX-8s and if that meant it would be offered, at some point, in a production car. He said the 20B had already been homologated. The answer to the second question was "No". :(

rx7 motor is build for Turbo

Renesis isn't

IIRC the corner seals on pre-Renesis rotors aren't able to seal proper and (I think) are at some point completely unsupported by the side plates. Awhile ago someone posted pictures of this. I'll try to find it.

quattro

Fitment
 

Will an RX7 engine fit on the same motor mount locations as a Renesis and are they both dimensionally the same?

I know one reason is the exhaust port. The side exhaust port on the renesis was done for emissions, and given the thickness of the material around it, does not take well to porting. A peripheral exhaust port is better for performance...

...or so I remember overhearing at the Mazdatrix booth at 7stock.

Are you sure you don't mean the side seals? I know they moved the side seal further out at the apex. I didn't think one could move the corner seal much closer to the apex than it already is.

For race use an all peripheral port engine would be a better option than an all side port engine. Even those running streetport style 13B's have the advantage over the Renesis of lower compression. The side exhaust ports can be an issue with really high horsepower as the housings can warp in this area if submitted to lots of heat. For race use where reliability is a concern, the 13B or 20B is hard to beat. It's proven.

For street use however I prefer the Renesis. Preferably the '09 Renesis as it has some improvements over the pre-'09 engine. In fact if I ever have a 3rd gen, the first thing I'd do is to take the engine and turbos out and throw them away. Then I'd replace it with a Renesis, an aluminum flywheel, a 6 speed transmission, and no turbos. That may sound sacreligious to most but that would be a far nicer car than stock. Definitely just as fast which is fast enough and it would be far more reliable.

I can relate to this for sure.

older 13B motor has different ports that flow better for turbo applications. while the new 13B is a great NA drive every day motor it isnt one that is favored on the track.

That's a hell of alot better than throwing a damn v8 in there. :lol:
I'm surprised you don't see more Renesis engine swaps in older RX's?