I have been building a new 13 PP motor this Spring for a rally RX-7 that gonna compete in a tarmac cup in Sweden this summer. Here are some specs:
RX-8 10:0 cr rotors
PP with intake porttimes as factory race D-port with a 42mm throat, exhaust as close to factory race spec except for earlier opening timing.
Hurley 2 mm Apex seals
Balanced assembly
Weber 51mm with 43 mm chokes and 5" air horns
F-7 e-tube 250 main jet 160 air jets and 1 mm squirters
ProSpark distriburless ignition with 4 coils
650 mm header with 50 mm innerdia and a 3" exhaust with one Apple 600 mm full flow silencer

I have built a very similar engine 1 year ago that made 276 hp with same port timing and flow numbers so i had hope for little more power.
First pull of the day was only 237 hp with a conservative timing L=15' T=10' and 44 mm chokes.
Switched to 43 mm chokes and upped the timing to L=18
T=13 this time the peak numbers were close to 260 hp.
I had so far used 2 mufflers, 1 presilencer and 1 full flow
3" mufflers, then i switched to the Apple racing 3" muffler and picked up another 8 hp! Still not satisfied i re jet the carb and raised the ignition to L=21 T=16 and did some minor adjustments to the float bowl and after some more pulls i had 284 hp@8600 rpm and 180 ft/lb@7500 rpm But the biggest improvement was in the 5-7000 rpm band where i had 11-20 more hp compared to last years 276 hp motor. Maybe i culd have tried a few more ignition degrees but didn't dare if knock would occur. Of the 4 PP motors i have dynoed this was the most driveable motor dyno man Pär said with a power band from 4500 rpm (145ft/lb) to 9000 rpm (155ft/lb). One thing i noticed with this motor was that both the engine temp and oil temp was up 10-15 degree Celsius with the same Motul oil and Inugel expert cooling media that i always use. What you guys
think is it the higher chamber pressure that the water and oil system can not handle. The exhaust temp was close to last years motor peaking at 845 C compared to
860C. Is there any body who have done some testing with RX-8 rotors and have some numbers to share

 

Sounds really good!Great numbers your getting!

I understand from what your saying,that it had more midrange?.Which is a great achievement for a PP motor making that HP.

Congrats! I enjoy someone that experiments with different components,to do something new.

Any sounds/pics of it perhaps ?

Karis

 

If those are engine dyno numbers the torque seems a little low. I may be horribly wrong, but I would normally expect closer to 200lbft torque for a peri. However maybe you have just traded off well to get the wide power band. And of course there are all varieties of PP from tiny (NSU) to huge. Very good though

On the temperature issue I would have to think. Certainly the rotors are less massive so likely to conduct more heat through to the oil, but there must be something else going on

 

yuh,with the lower exuast temp and high engine temps, maybe the rotors are absorbing more heat

 

good to hear
what apex seals are you using

 

I wonder why not use 58mm IDA from GENE BERG.

 

If it runs best with 43mm chokes, I don't think getting a bigger carb would help at all.

 

Well i really try to get some more torque of my PP engines but with the last 4 i built there is always "only" 170-182 ft/lb as best. The engine dyno is very conservative so with the engine in a car and on the rolling roads.. I have assembled one factory PP engine and it was dynoed on an Australian rolling road (don't know it's name) and that one made 318 hp translated to fwhp.

 

2 mm Hurley race seals.

 

Cost to much and my customers don't dragrace, otherwise i will go electronic fuel injection

 

Yeah i think so to! The inlet min throat dia is only 42 mm, i know dragracers in Usa use up to 2" inlet dia for higher power peak and higher 7-11000 rpm powerband.
I build my motors for rallycross and rally so i have to have a 5-9000 rpm band.

 

Sweet to hear that your new motor is stronger than the old. Did you mess around with different length airhorns at all?

Question about the RX8 rotors. I read somewhere that they have a slightly different rotor depresison, that is more like the older engines. And that it's shape yields it self to really advanced timing, is this true or a bunch of BS.

 

wow that's amazing!!
I'm starting to grow facinated with PPs....and those numbers are definitly impressive for an NA rotary!

 

The depth of the bathtube chamber is only 5 mm for RX-8 rotors compared to 12 mm for 89-95 9.0 c:r rotors. The depression is what i could measure same as 89-95 rotors with a feeler gauge measuement of 0.5-0-7 mm against the trochoid curve.