Is Fmod just a way of creating samples to use? Or is it an engine which the game must support in order to use it?
The last sample, #3, sounds great. I would however increase the pitch a little at the top end. As the revs get higher so should the sound/pitch. I hope this makes sense.
But if it's supposed to be a corvette engine and it's sampled off a Ford engine why does it matter if the others sounds are good or bad? Only one sample sounds like a Chevy.