Nitrous oxide has a bad rap, and the reason it has a bad rap is the same reason it is so great: it’s easy. Too easy; for about $500 and a few hours of work, you can add basically any amount of power you want. If you are a reasonable person with self-control and a nitrous controller, you can add 35 horsepower to your Ford Mustang and be totally content. This is, of course, a fictional situation because nobody who drives a Mustang has that kind of self-control.

http://www.motoiq.com/MagazineArticles/ID/4685/So-You-Want-To-Use-Nitrous-Oxide-Without-Blowing-Up-Your-Engine.aspx