I said it in another thread, American V8's. More specifically just a Mustang/Camaro V8 hybrid that can compete in the GTR class. 400 some odd horsepower, torque can be their advantage, rpm redline can be their disadvantage (though not sure anymore what v8's rev too, unlike the muscle car era).
I'll second the AC Cobra. This car is a must in any racing sim!!! It is almost everyone's dream car.
This has been said before, late 60's early 70's era American Muscle cars. Mustangs, Camaro's, Baracudas, Trans Ams, Chargers, etc.