No matter what forums i've gone to one of the first mods they suggest is a CAI. Either in your fender or in a heat shielded box. Well i'm here to tell you, a CAI will NOT add horsepower. ok maybe that's a little of an overstatement.
The theory of a CAI adding horse power is usually based on two statements
A. if the motor can get air in faster it can get air our faster.
B. Colder air is denser air.
Now to discuss both these accusations.
A. Your motor in essence is a vacuum. sucks air in pushes air out. simple, but it really doesn't matter how much air you can suck in if it has no place to go. On most factory cars the exhaust is pretty restrictive due to emissions. so no matter how open your intake is you will only be able to push a certain amount of air through your motor with out also opening up your exhaust. think of it as putting your hand over the air release on some shop vacs. as they suck in they collect the dirt and push the air out. Now put your hand on the intake part of the vacuum and then cover the exhaust port of the vacuum you'll notice a huge loss of intake flow. no matter how big or open that intake hose is. the phrase (more air = more power) does come into play here. but how much more air do you think is coming in? if you have a boost vacuum gauge this will make more sence. let your car idle.. read the vacuum. say 23lbs of vacuum now take your intake hose 100% off and check again. itll most likely be 23lbs of vacuum. no matter how open your intake is it will always have that peak vacuum it can hit, now with forced induction (turbo, supercharger) the air is forced into the motor causing your vacuum pressure to increase. say at 3000 rpms your vacuum with out forced induction is 29lbs. now say you run 10lbs of boost. in reality your engine now has 39lbs of vacuum it can use to intake and push out causing more power.
B. Cold air is denser air. well this statement has truth to it. but in this context, how much good will denser air be if your not also getting the flow of fuel you need. the typical engine ecm can compensate up to a 7% change in air density and compensate by either adding or taking more fuel. thats why you get different gas milage at different altitudes.. if the density of the air you suck in through your intake is more of less than that 7% it is diong no good (without a pcm tune)
all in all, what i am saying is, CAI's may sound cool. but they really aren't worth your money adding until you can modify either the pcm or your exhaust system.
short little rant. (cant comment in the rant section yet)
