I have Android version, and i can clearly hear turbo while driving my F50...

It seems they used engine sound from some other turbo car in game (F40?)

We all know F40 has V8 twin-turbo, F50 engine is V12 normaly aspirated.

And why there isn't a car spec button in car preview screen, that would be

some 100kb of additional data for all 93 cars in rr3 ?