If you do an online search for “air filter test” there is a lot of very good information. IMHO, the CAI units are NOT WORTH THE $$! Unless you are talking about a system that was specifically designed for a specific application there are very little hp/tq gains actually achieved in a street use vehicle and there are very few docs that these mfg’s can produce that actually show an increase in hp/tq in the power-band range of a relatively stock street vehicle. As an example, the 5.4 V8 if close to stock can only suck in a maximum of 480 cfm and a flat panel filter will flow 500 cfm, there is simply no way any CAI on a relatively stock engine can "increase the air flow" above and beyond the engine ability to injest......just a fact of physics- and while they do have CARB approval, CARB does not look at whether they perform as marketed, they only look if the emissions are being met or modified.

I would avoid oil impregnated filters. While they have their purpose in off-road applications, Ford/GM/Dodge all have “watch-out” bulletins where the oil has contaminated intake sensors. - they even have a training video for the techs on this (flatratetech.com) . I have personally been the recipient of a very well Ford documented event involving a new- out of the box K&N filter in a brand new vehicle (yes 1997, 4.6 Cougar Sport), where Ford replace the MAF 3 times and finally determined the cause of the failure was oil contamination. All documents including the original receipt were delivered in person to K&N staff, with only a return of the filter & refund (which was purchased directly from them), which was "ignored" on multiple occaisons.

Now for some science.......If you look at the flow data, WIX HP filters flow 98+% of K&N and have a much smoother flow post filter plus excellent filtering, for a fraction of the price! The OE’s have an excellent air intake system. What many view as an issue (is the plastic intake tube with its noise canceling design) actually increases air pressure. It is the same hydraulic concept used by fire fighters creating water supply where psi is low. By having the air cross the path at a 90 degree angle, the pressure is increased proportionally. Fire fighters use what is called a “4-way valve” or “Blake Valve” at the hydrant where the water is cycled through the fire engine (pump) and sent back into the valve crossing the water flow at a 90 degree angle. In this case it also acts as a sound canceling device! At low speeds, this can reduce the flow a tad (which is what most “feel”), but in terms of peak hp/tq, a good high flow filter is all that is needed. You can use a WIX OEM HP replacement filter in the OEM plastic manifold box and either remove the plastic tube and replace it with a piece of pipe/hose, etc or remove the tube completely and replace the tube by building an air ram type intake into the air box manifold (where the pipe use to attach)- make sure it terminates above the fan shroud to avoid water intake or fan induced pulsations.