Decrease time warp:
Pause the game, press R2, L2, L1, R1, Left, Left, Left.
Invisibility:
Pause the game, press R1, L1, L1, R2, L1, L1, L2.
Lighter cars:
Pause the game, press L1, R1, R1, L2, R2, R2.
Increase time warp:
Pause the game, press R1, L1, L2, R2, Right, Right, Right.
No gravity:
Pause the game, press R1, R2, R1, R2, Up, Up, Up.