I've been struggling to synthesize satisfying engine sound and tire squeal for a game, my best efforts sound like an engine that runs on soap bubbles. I think the cutting edge solution involves harmonic analysis of samples to find or make smooth looping points within the engine cycles. Crankcase audio has some tool that does this https://www.youtube.com/watch?v=kpeJdErx5b4 . Way too expensive for me though.