Start a new game from the very beginning of the story mode. You will have to enter a name for your hero from the bunch of Japanese letters.
Now enter the following Japanese hiraganas: MaKeINu. You will now have the jet engine. Select it in your dining room. Later in the races, press L and R at the same time to activate your jet engine. Your car is now ultrafast!
By entering the name "Go Ki Bu Ri- Na" in hiragana when the Story mode starts, you can enter the sound test mode.
Start a new game with the Story Mode. Enter the name "Me Mo Ri" in katakana and then "Ke Shi Te" in hiragana, that's "MeMoRi(katakana) KeShiTe(hiragana)".
Boom! All your game saves are now gone!
Go to the pit shop. When the keeper greets you a "irasshaimase" (Welcome), hold down X, and press left, up, down, down, up, right, up, down, down, up, right, up, down, and down, and then release X. You now have the "torakushon C" (Traction C) installed in your car.