When you win the cup in the Grand Finals the best car in that class will become unlocked.

Unlock Bullet Gt:
Win Street Finals.

Unlock Venom:
Win Derby Finals.

Unlock Insetta:
Win Race Finals.

Try entering these codes if you need some help in the game, to enable them go to 'Extras' at the 'Main' menu and then to 'Enter Code'.

Unlock ALL Cars and 1 Million Creds:
Enter the code GIEVEPIX

Unlock ALL Tracks:
Enter the code GIVEALL

Unlock Flatmobile car:
Enter the code WOTKINS

Unlock Big Rig:
Enter the code ELPUEBLO

Unlock Big Rig Truck:
Enter the code RAIDERS

Unlock Pimpster Car:
Enter the code RUTTO

Unlock Rocket Car:
Enter the code KALJAKOPPA

Unlock Mob Car:
Enter the code BIGTRUCK

Unlock School Bus:
Enter the code GIEVCARPLZ