The engine sounds pretty good, not quite like the real LT5, but convincing enough. However, the C4 Corvette is a very noisy car. Lots of wind/road noise and it rattles like mad on the track. (Maybe this is only my own car?) Perhaps you can give those sounds a boost?
Also, the AI cars are quite a bit louder.
When this is all sorted out, this mod will be a must have.