The stock air box, while having dual inlet 2.5" pipes, tapers down very tight as it approaches the MAF. The cross sectional area of the 3" intake tube is numerous times better then the stock box. Plus we have a 3.2L nonhighrevving motor with 215 hp, 3" is probably over kill on these motors as it is. Believe me if 3" works for 500 hp+ V8s it'll do just fine for our cars.