Here is my story.

Changed my S5 engine with an S4 short block streeport. I was doing my break in procedures. Everything was super fine until I arrived at the step of 5500 rpm. The engine shackes and I felt it under my seats (tranny suports). Then, just by revving it on neutral, small vibrations began around 4000-4500 rpm...

I've talk to people and they suggest it is the flywheel. I've put an S4 flywheel on my shortblock, but I bought from a guy that told me it was an S4. Didn't check the number on it, but I thought it was ok cause it was different from my previous S5 flywheel. Could it be a turbo flywheel ???

I want to know everything I have to check before I pull the tranny down... any suggestions that could cause the vibrations at high revs ? Already bought a S4 flywheel (326). For now, the rest of the car is completely stock except for an high flow cat.

Thanks

 

does it do it while your under load?

 

No... it's only at high rev. I don't think it's the engine mounts.

 

without knowing for certain which rotors and front counter weight are installed in the motor you can only guess as to which rear counterweight the motor would like.

who built the motor? it could be miss-matched rotors, wrong front weight, or wrong flywheel.

 

RX7 specialities built it in Calgary, Canada. It's S4 rotors and I really hope that the front counterweight is the good one...

Is it possible to install turbo flywheel on NA engine ? Cause the flywheel was different, but could it be a turbo one ???

 

No, the turbo flywheel is bigger and a non turbo clutch wont bolt on. I'm not even sure if a turbo flywheel will fit inside of a N/A bellhousing.

 

Does it always happen at high rpm? Even if you hold the clutch in?

Your motor mounts should be easy to check, I would try those first.

 

It happens even when I hold the clutch in and it has nothing to do with speed I'm going.

I could check the mounts cause it's easy to do, but I doubt cause it does nothing when I kick it.

 

Is it possible to verify if I have S5 or S4 rotors ???

 

Maybe, S4 rotors have a rough cast finish on the rotor pockets and the S5 is a machined finish. You could peak in the exhaust manifolds but there may be too much carbon to really tell.

 

Problem solved.

Might help someone: just had to change the fan. 4 bolts, that's it !!! Probably too resistant so it turned with the engine at high rev and made it vibrate !

So dumb... I freaked out for nothing !!!

Nic

 

Thank god for this thread, after alot of cursing, I found this thread with the simple "rx7 5500rpm" on google.
Took my fan away, and problem is gone!!

Yehaa!