To use these cheat codes, goto the main menu and click "Create Player" and type in the cheat for the name. Click "Done" (you'll hear a little confirmation sound). Then choose your regular profile and play the game!
Gulliver
The Porsches are all shrunk down to the size of radio controlled racers and have little antennas.

Smash Up
Using the Skidpad, Destruction Derby style racing - nothing better than that!

Dakar
Tired of Street Racing? Changes car physics and tracks to Rally style.

Fuzzyfuz
Enables cops in quick race (cops may not appear on all tracks: i.e.-Monaco).

yraGyraG
Enables all cars to have 993 physics.

fetherw8
This cheat code makes cars way heavier.

Booster for Speed
Go to the (Single Player mode) and put in "freewill" as your name. Now in every race you do you can double your speed, breaking every record.