Press Up, Down, Up, Down, Left, Right, Left, Right at the 'Press Start' screen. If you entered the code correctly, a message will appear stating that you have unlocked a "Special Challenge Event" will appear. At the main menu, select the "Challenge Series" option. Scroll all the way to the bottom and choose #59, the Burger King Challenge. Successfully complete the challenge to be able to use all Junkman parts on cars you have in "My Cars". Note: Before applying Junkman parts, press A in the performance parts place to get them as high as they can go, then apply Junkman to each part. By doing this, it gives better stat raises.