To make your car invisible (but the cops can still see you) just pause the game during gameplay and press R1, L1, L1, R2, L1, L1, L2. You'll hear a sound when you enter the code correctly. If you want your car to be visible again just re-enter the code at the pause screen. The code will also reset after you start a new mission or quit out of the one you're currently in.

To make your car super bouncy like there's very little gravity just pause the game during gameplay and press L1, R1, R1, L2, R2, R2. You'll hear a sound when you enter the cheat correctly and will remain active until you either quit out or beat the level.

To make the game play faster, including how fast the clock counts down pause the game and enter R1, L1, L2, R2, RIGHT, RIGHT, RIGHT. You will hear a sound when done correctly. When you quit or start the next level the cheat will be de-activated and you'll have to re-enter it.

To make the action and time clock move really slowly just pause during gameplay and enter R2, L2, L1, R1, LEFT, LEFT, LEFT. You will hear a sound when entered correctly and when you return to the game the effect of the code should be quite noticeable. When you start the next level the code will be deactivated.

Have on your memory card a Midnight Club save file to unlock cars from that game.