Go the the Main Menu, then Extras and then enter the following codes to activate the listed cheat effect.

Effect	Code
AAA Shell	Chet, Skidmark, Smooth Move, Skidmark.
Firestone Shell	Turbo, Whiplash, Turbo, White Shadow.
New Shell #1	Skidmark, Whiplash, Turbo, Skidmark.
New Shell #2	Smooth Move, Turbo, Burn, Smooth Move.
New Shell #3	Smooth Move, White Shadow, Smooth Move, Turbo.
New Shell #4	Turbo, Chet, White Shadow, Turbo.
New Shell #5	Whiplash, Skidmark, Smooth Move, Whiplash.
Play as Skidmark	Skidmark, Whiplash, Turbo, Burn.
Reverse mode	White Shadow, Turbo, Smooth Move, White Shadow.
Turbo's original racing shell	Burn, Smooth Move, Turbo, Burn.