Win the indicated group to unlock the corresponding car:

Apachee 200X: Finals Group A
Bornbad GT90: Professionals Group B
Buster GSt: Amateurs Group B
Firespitter RS: Professionals Group A
Incubator V12: The Final Fight
Ironhorze V8: Professionals Group B
Pick'Em'Up V8: Professionals Group A
The Wrecker: Finals Group A