D1 Grand Prix Cheats

Bonus cars:
Beat that particular opponent and you will unlock its corresponding car.

AE86: By defeating Keiichi Tsuchiya (opponent 32).
B310: By defeating Zaku (opponent 5).
Cop Car P34: By defeating opponent 38.
Eclipse Advan JZA80: By defeating Manabu Orido (opponent 20).
RB1: By defeating Manabu Suzuki (opponent 10).
Stream Option Z33: By defeating Daijiro Inada (opponent 15).
Taisan Benihana Viper: By defeating Tarzan Yamada (opponent 26).

Extreme mode:
By winning every season in the D1 Series (including Custom) and finishing Survival mode.