To unlock more cars, you simply need to complete more Boss levels. The Porsche Carrera GT can be earned after beating Blacklist Boss #3. The Subaru Impreza WRX STi requires you to beat Blacklist Boss #9. The Mercedes-Benz CLK 500 can be enjoyed after winning against Blacklist Boss #8, and driving the Toyota Supra means you beat Blacklist Boss #13.
You do not need to upgrade prior to a Boss level. Your car should last for several levels as is.Learn more about Adventure Games