Every cold air intake has an air pod which acts as a filter for dirt and crap from the air, to put it simply, a CAI is a metal pipe connecting to the throttle body fitted with an air pod at the end, and the air flow meter somewhere in the middle of the pipe, look them up on the net, you will see what i mean. Its less restrictive than the original air box, as more air enters the pod, and since the pod is located away from the engine bay, colder air enters the engine through throttle body via the pod and pipe. Since colder air is much more dense than hot air, when it mixes with the fuel in the combustion chamber, there is more of an explosion as there is more oxygen to burn, and you get more power.