[MB38]

On a very basic level, nitrous is used because it's damn cold. When you do a basic intake setup, nitrous is sprayed directly into the intake. It instantly cools down everything it comes in contact with, be it air or the piping itself. As you should know, colder air = denser air. The colder the air getting into your engine is, the more air is getting in, the more power you make. That's a simple setup.

Several companies make an intercooler sprayer. Nitrous (or CO2 in some cases) is sprayed directly onto the intercooler fins. This works like an intercooler water sprayer on steroids and cools the air passing through the intercooler that much more.

Some systems pass CO2 through the fuel rail, cooling the fuel. I'm not as clear on this concept, but I suspect that the colder the fuel, the colder the air it mixes with, leading to the same end result. One product similar to the fuel rail cooler is what's known as a "NOSzle." The standard fuel injectors plug into these nozzles, and the nozzle plugs where the fuel injector usually would. As a result, nitrous flows directly in with the fuel, causing the same end result. These are popular due to their simple installation.

The "best" form of nitrous usage is what's called "direct port nitrous injection." In this case, holes are actually drilled into the intake manifold runners. Each runner gets its own fogger. When the nitrous is activated, nitrous is sprayed directly into the runner. I'm not as clear as I could be on this type of injection. I know it cools the air, but I believe nitrous ends up getting into the piston and explodes (in addition to the cooling effect). I very well might be mistaken here, so wait for somebody else to clarify.

The purging that you've probably seen in videos/movies (for instance, 2F2F) is exactly that. When the bottle is in the trunk, a rather long line must be installed to connect it to the engine. As a result, the liquid nitrous in the line will begin to dissipate when not used. It will collect in the lower points of the line and the rest will be a gas. Instead of firing this potentially dangerous and uneven mixture into the engine, a button is pressed which vents the compressed gas to the atmosphere, allowing the line to fill with liquid nitrous again.

Hopefully that helps a little.