Cool Air vs. Hot Air

Hot air balloons float because the superheated atmosphere they contain is far less dense than outside air. Since engines require oxygen to produce power, the more dense and oxygen-packed the incoming air is, the more power the engine will make.

Types

Cold air intakes come in two basic flavors: Ambient Pressure and Ram Air.

Ram-Air Intakes

Whereas Ambient Pressure intakes simply siphon off cool outside air to feed the engine, ram-air intakes take this effect a step further by facing the intake forward. This causes the high-pressure air ahead of the vehicle to cram inside the intake, creating a slight supercharging effect as vehicle speed increases.

Hood Scoops

Hood scoops have gone out of fashion with the rise of fuel-injected engines, but remain one of the most effective air intakes available. Not only do Hood Scoops ingest cool air, but their very short intake tracts can help them to better utilize the ram-air effect of their forward-facing design.

Throttle-Body Mounting

Modern cold air intakes are usually a section of plastic or aluminum tubing from two to four feet long. These intakes often have a cone air filter on one end, and connect to the throttle body on the other.

Source:

Consumer Reviews

Nextag

Air Intake Product Review

Resource:

RSX Cold Air Intake Review (Video)