On a race car where you are rebuilding or at least refreshing the engines after every event a cold air intake and K&N can give you a couple HP. For everything thing else they are a waste of time UNLESS they are a true cold air intake that can provide a bit of ram air. Not going to happen on anything that doesn't have an airbox with it's intake in a high pressure area. That was why the old muscle cars had the ducted intakes pulling air at the high pressure areas in the grill or at the base of the windshield. Even then they were a marginal improvement unless the car was moving fast enough to create any pressure.
As for any of the underhood kits, they are ALL a waste of time and money. Think about this, which area on a vehicle has the highest temperature air in it? The converters, then the engine compartment. Now look at where the converters are on modern vehicles! In the engine bay! Then they add a lower air dam to push air out from under the vehicle and a drip tray or skid plate to make the underside slick. Both of which block airflow and heat up the engine bay more. The stock systems draw in air from a fender well or up front of the core support through an insulating plastic tube and housing, trying to get cooler air. What do 99.99999% of the cold air kits do, remove all that, then add an open filter with maybe a heat shield, and metal tubing all pulling air from under the hood. Yeah that will help!!! As for the "they allow free airflow, maybe but VERY doubtful that is what you want. On a MAP system the airflow isn't as critical but on a MAF vehicle that free turbulent air can cause a lot of problems as the stock systems are designed to provide a more constant wave of air through the MAF, that is why many have the honeycomb in them, to better measure the air. With turbulent air you get an inconsistent charge, and worse you could create a system where the sensor is in dead air and really cause problems.
