After you've become World Grand Prix Champion, turn on the system and hold A + B when the screen "Now loading the data from controller pak..." Now go to the Driver Selection screen and the '96 Forti drivers will now have an Ubi Soft Original H-RA V12 Car.
Note: You need a controller pak to do this code.
Unlimited Fuel
In any Grand Prix race, set your fuel to 10% before starting to get max acceleration and don't worry you dont lose any fuel during the whole race!