A lot of the race cars sound excellent to me. I can tell if the car passing me is the 787b or a 12 cylinder. The idea of changing the exhaust system in a race car is probably not super realistic.
I know some of the modded exhausts sound the same (though they sound good, they clearly didn't modify the exhaust on all these cars and record it). Otherwise, I think the cars generally sound great and matched if you stick with the original stuff.
Anyway, it's over 1000 cars, and they did a good job making the cars sound good, at least in my opinion.