Best parts are the engine sound under load, slight delay when opening throttle and changing down a gear to force engine braking.
Are exhausts/mufflers modelled?
For ages I've wanted to simulate different designs for exhaust headers and systems, to be able to possibly create different/interesting sounds from certain engines - i.e. can you add some additional headers with a different length and make an I4 sound like an I6?
Live for speed IIRC did have a fully synthesized engine sound but most games now have samples and some clever interpolation / synthesis as mentioned by others.
"Simulating an Entire Car Engine (yes, it makes noise)"