5. Underground Racing
Car: Audi R8 GT
There are those who are happy spending $200,000 on an Audi R8 GT and are pleased with the 560hp 5.2-liter V10. Then, there are those who think that's weaksauce and install twin-turbos into the insane road car that already gets to 60 mph in 3.6 seconds. Underground Racing helps those who fall into the latter category. The custom shop developed a kit, split into four stages, that can get you up to 1,500 horsepower on a heavily modified race-ready engine when using 117 octane racing fuel. With the stage 3 kit using regular gas, it still gets up to an estimated 1,000 horsepower. The stage 3 kit will cost you another $94 grand. If you're interestd, you're going to have to be patient. The kits would require refittings throughout the engine and can take up to a couple months to complete.