Beat the game and become World Champion. Then save the game to a control pak and restart the game. When the words "Please Wait While Loading" hold A B. Now go to the Car Selection screen and you will see a new secret car.
Beat the game and become World Champion. Then save it and restart. At the Driver Selection screen highlight a driver and press CLeft or CRight to change the current engine.
In Grand Prix Mode set the Fuel Setting to 10.