Need for Speed Underground Rivals Get the Edge in Drag Racing: In drag racing, rather than holding the nitrous button down, tap it. Your car will gain speed faster. Freeze the Computer: When in Lincoln Connector, simply force your computer opponent into the first shortcut you see. Once in there, the computer will freeze for a while, letting you get a huge lead. Unlocking The 4 Boss Cars: Getting a chance to race the Boss Cars depend upon what level you are racing at and what car you are using. In PRO Level Boss Races, keep changing your car until you get the race you want against either the Subaru Impreza or 1969 Dodge Charger. In MASTER Level Boss Races, you may also have to change your car until you can race the Chevrolet Corbette Z06 or the Nissan Skyline R34 GTR. You will have to beat these Bosses in other Boss Races in order to unlock them.