It turns out that the only thing worse then programmer art is programmer sound. My game very accurately models automotive power trains, it includes engine rpm, power band, gear boxes, rear axles and wheels. I have good input, I need tips or outright help with making authentic sounding output.

I've had a peek at the resources used in some older racing games. I'm not sure if things have gotten more advanced in the past decade, but back then they seemed to record a real engine running in different gears at a mid-range RPM. They then choose the right sound to play based on what gear you're currently in, and then pitch-shift the sound based on your current RPMs.
This requires a lot of sampling and a lot of tweaking. I also have no idea how they edit the samples to make sure that they loop properly...