Originally Posted by Phatman
I thought it was because the Nitrous has more oxygen per volume then regular air, thus getting more air into the engine.
It's a bit of both.
When nitrous is heated (above 570F, I think) it splits into oxygen and nitrogen, thus making more oxygen available for combustion in the engine. And when it vaporizes, it provides a cooling effect on the intake air, which increases the air's density thus making even more oxygen available for combustion.
Not flammable at all.