Well, I would venture to say that all the kits are essentially the same in terms of loudness, although it really isnt anything until upper RPM's when really gunning it. The stock airbox draws air in from the kidney grill, so in terms of air temp it would be the same as a CAI, as long as you dont have an exposed element in the engine compartment w/o a shield. (I think air flow helps make those horses) Search the archives, as well as Bimmerforums; I have seen home-made kits, and maybe? a prduced kit that has the element in an enclosed shield that has a hose that goes to the front of the car; that may block some of the sound.