Vroom Box utilizes a powerful microprocesor to digitally recreate the sound of your favorite muscle cars, and syncronize them to the engine in your own car. So when you step on the gas, you get the powerful roar of a '71 Barracuda, a Shelby Mustang, etc. It sounds so realistic, it will blow you (and the guy next to you) away.

http://www.vroombox.com/