My friend has a C5 Z06 with a built/forged bottom end and a D1 setup that put out 690rwhp. After the tune was complete it was driven for a few days and WOT runs were made. Then after one particular WOT 3rd to 4th run, the motor cut and upon a restart, knocked badly, spit out plumes of dark smoke, then would not restart later after turning it off for a few minutes. After a tear down, they found a piston hit a valve and mushroomed, along with a crack in that cylinder. The tach was only brought out to a max of 6,500 RPM. I'm not sure what the limiter was set at.

My questions are:

1. Is there anything besides an over rev that could have caused this damage (bad tune, springs, etc)? I was told before the run the engine did this strange stuttering/cutting out thing a couple times, but didn't show any issues on the runs.

2. Is it safe to assume that revving a fully built and properly tuned motor of this sort to 6,500 RPM should not cause internal damage? Again, assuming the motor is built and tuned properly.

I'll see if I can get more specifics on the build. Just looking for any input. Thanks.

 

Was it #7 cylinder?

 

I'll ask him and let you know. Let's assume it was; I'm assuming that's significant?

 

I'd say that cylinder was detonating if I had to guess, and the motor wasn't overeved!

 

I talked to him and he said the piston to valve was in the number 5 cylinder. And the crack was in the number 7. Why do you say it wasn't over-revved?

 

Usually valve don't mushroom from hitting the piston, they just bend. If the head of the valve looks like it has mushroomed or gotten really concave and has grown in length, that's usually from detonation. Now there is a possibility that the valve spring wasn't good enough to handle the amount of boost/rpm and a valve did tag a piston though, causing other things to happen also. Check everything once you get it apart.

 

Thanks for the information, JPH. Can anyone else confirm what JPH is saying? (I'm not doubting at all, just looking for as much advice as possible as to what might have caused these symptoms).