No game has really accurate sounds. The Il-2 series all aircraft have the same basic engine sound, only change is that its louder in bigger engines and modulates for multiples.
A P-38 sounds the same as a 109, which sounds the same as a Sturmovic, which sounds an awful lot like a Tony...
Thats why the custom soundpacks are great. You can record the engine sound directly from a video clip of the exact aircraft you want and use it.