Use RX8 Engine Rotors in FD build or other rotor?
 

Doing a pretty big build and wanted some thoughts on possibly using RX8 rotors in my engine build. I previously considered NA 89-91 rotors for their lighter weight an higher compression (more torque). Then I was referred to 86-88 NA rotors, still higher compression (vs FD rotors) and stronger. I was wondering if RX8 rotors are a viable alternative? What are the benefits, costs, and risks for my setup. IIRC they are 10:1 compression.

The vehicle purpose is for autocross racing. I would like to make power reilably till 9000rpm and make torque down low in the rpm range.

The engine build will include:
Street Port
RX8 Eshaft
Balanced rotating assembly
RA Black Apex Seals
OEM gaskets/other seals
Race Clearancing (do I need this if I get the rotating assembly balanced?)

(note: turbo is a T04E with a 60 trim, and will most likely stay unless it's been compromised by the apex seal. peak boost will be around 18psi on 100 octane)

I think the RX8 rotors have problems with the thinner apex seal going over the exhaust port, but maybe you can make the groove deeper and use FD apex seals?

Aren't the stationary gears different?

The rear stationary gear requires a "grove" to be machined into the bottom of it (like the FD's) for a O-Ring, to seal the oil from the rear of the engine, other then that, you can use the gears in a REW


J.

There are a lot of differences between the Renesis and REW rotors. The Renesis is a much better/modern design for sealing, lower emissions, etc but it is made for side exhaust ports and all the main rotor seals are different:

https://www.rx7club.com/attachment.p...1&d=1288939557
Source: Ohkubo, "Developed Technology of the New Rotary Engine (RENESIS)," 2004 p. 11

The Renesis rotors also have a cutoff seal which is another thing to deal with. I just don't see enough benefit to using them.

The series 5 9.7:1 rotors would be ideal if you are ok with having a compression ratio that high. The series 4 9.4:1 rotors are heavier so you will need to take steps to balance the assembly. They also have sloppier manufacturing tolerances, and thus the compresison ratio can vary by as much as .3:1 . The combustion recess (bath tub) is cast on series 4. Series 5+ has a machined combustion recess, are 14% lighter than series 4, and have better manufacturing tolerances. Series 4 are generally considered "stronger" rotors but that probably won't matter unless you are building a huge HP monster. They have thicker internal ribbing than the later rotors (3mm vs 2mm on series 5+)
(Source: Matsuda, "New Technology Employed for the Latest 13B-Rotary Engine," 1990 p. 9)

Thanks! Since I already bought the seal kit, I'll stick with 13B rotors. Sounds like S5 Non-Turbo will work best for my application. HP goal is around 400-450.

Anyone know where too look for good condition S5 Non-Turbo rotors?

Has anyone ever cracked 400Rwhp with that small turbo? Why not go sequential BNRs. Thats what Chadwick runs and Im pretty sure he is competitve on the National level:nod:

I beat Dan at nationals with this turbo. (sorry Dan).

Edit: I think Dan runs modifief Jspec twins. Regardless, this thread is about rotors not turbos. I think he runs Racing Beat lightened S5 high compression NA rotors.

9.7:1 rotors and a T04E with a twin scroll manifold would be very responsive, although you may have to wind it out to 20+ psi if you really need power. Controlling detonation would be the biggest concern.

Kevin Landers of rotary resurrection may have some. kevin@rotaryresurrection.com

I run 99 spec twins.

LOL, but you didn't beat Brian in my car at Nationals :P. My 99's are not modified and the S5 NA rotors are not lightened. The rotating assembly has been balanced.

Dan

Yeah. Car sat solidly between both of you in the final standings, which I was thrilled about. You boys can certainly drive. I had to call out that little glory when djseven bashed my single setup (lol). Regarding the modded turbo, I was just referring to the fact that you modded the wastegate / pre-control system. I am glad to hear that the S5 NA rotors work well without the $$$$lightening$$$$. Where did you get your rotating assembly balanced?

That chart implies that REW's don't have oil control rings...?

^ The REW doesn't have a cut off seal. The cut off seal is a new combustion seal on Renesis engines only, because of the side exhaust port. It's designed to reduce the internal EGR effect by blocking exhaust gas from diluting the intake charge. The reduced EGR allows the Renesis to idle at 14.7:1 AFR normally, with stable combustion.

https://www.rx7club.com/attachment.p...1&d=1289259971

Thanks for clarifying. It was the arrow on reference image above the chart that had me confused.

Don't waste your time with renesis rotors. Rx8 e-shaft is about half a lb lighter but weaker. If I recall correctly it is not forged. I have heard of several breaking in higher hp builds.

rx8 rotor with 3mm seals has been done

CLR Motorsports

It actually idles at 15.0-15.1 AFR and cruises at 14.7 AFR.

I wouldn't want to use RX-8 rotors in a build that plans to go to 18 PSi due to the higher compression. What is wrong with FD rotors? They're the lightest (excluding RX-8) and are still high boost friendly.

thewird

Stick with an FD e-shaft. The RX-8 shaft is weak and I have seen it twisted and bent in a mild turbo engine.

if any one is interested in N/A FD

rx8 rotor with 3mm seals has been done

there is a 12page thread on this forum about it

it was installed in 13B PP N/A FD3S race car .... that made 250 RWHP and they are hoping to make 280 RWHP when its all done

search it and you will fined the thread

as far as boosting on rx8 rotors inside FD engine you should be ok with 10pis max but thats it......- you might as well get a rx8 and slap turbo on it


bout if you wanna go N/A and make some power what i would wanna do is
20b PP with RX8 rotors or ( light weight FC3S N/A rotors) on E85 now that would be SWEET -- i would throw out my current single turbo setup for this

^ I've tuned an RX-8 to 12 PSi on pump gas which has been running for a little under 2 years now with a few track days. This year he's porting his motor and installing 3mm ceramics and we're gonna add some AI and crank up the boost. Note, there is nothing wrong with the motor, he just wants more p0w3r.

thewird

every time I've driven an rx8, it just screams for boost