The K&N drop in adds about 3 extra HP and the K&N CAI adds about 12HP, the Airaid adds 15 HP. Airaid and K&N oiled filters are the best at removing the smallest particles of dirt and Airaid has just released their synthamax non oiled filters which are supposed to be just as good as the oiled filters.
Air can speed up appreciably with negligible increase in drag inside a tube to fulfill flowrate. As long as it isn't reaching extreme "terminal velocity" sort of speeds, it should be fine. The filter is more critical because it IS highly influenced by air velocity. That is why you typically want a large surface area of media...to ensure the local air velocity is very slow and triggers the least amount of drag as the air passes through the media, for a given level of filtration. Once through, the air can speed up appreciably through a smaller tube with little negative impact to fulfill flowrate needs.after thinking about this for a minute, i wonder if filter area matters at all.... the inlet tube size will be the limiting factor. if the tubes are the same size and are smaller than the filter area, shouldnt that be the biggest restriction? as long as the filter is big enough and flows free enough, you can start talking about the flow thru the tube
3.5L Intake Evaluation (E-Bay, K&N, Big Bully, Air Hammer HO) Once again here is the link showing a 12 HP gain with a CAI.Those number are no where near correct. That is like magic dreamworld where Racing stripes add 25 horsepower.
It all depends on where the restriction is. If the restriction is the Throttle body nothing you do will matter unless you get a ported/larger TB.If anything, I like the reusability of the filter. I install K&N in everything I own just for that sake. I'd be curious too if a larger inlet tube would help. Probably not on these computer controlled monsters, but on an old computer controled carb 305, increasing the snorkel size and running hoses to under the front bumper slashed a half second off that tub's 0-60. 11sec down to 10.5!!! WOOHOO! lol