CAI kits
is it a HUGE difference? no probably not.
are you also asking about CAI with bigger inlets than the maf and why they do this? well it's because when going through a filter the area of entry actually becomes smaller than the physical size due to having to pass through a restriction. as long as there is velocity there is nothing wrong with trying to get as much air into a motor.
if you want to save some money on an intake look for someone selling a used CAI. I bought my old K&N FIPK for around $100 or so and sold it for the same.

