cold air intake

ok, what exactly does a cold air intake do?
how much increase in power does it generate?
how big a hit on mpg does it normaly take?
how likely is it to screw up the car?

A CAI put the air filter outside of the engine bay, usually in the front fender. This allows the engine to breath in cooler air and therefore make a little more power. Expect a 3-5 hp increase from a decent CAI.

so it wouldnt effect fuel efficincy at all right?
thanks for your help on this one

most company clam about a 2% increase in fuel efficence. what engine do you have?