Originally Posted By: Shannow
member ran some very good tests a while ago, and they are at the front of BITOG,
http://www.bobistheoilguy.com/airfilter/airtest1.htm
According to the test,
"...I always heard on the 'net that paper filters best. It does, but it isn't as superior as I thought it would be. The K&N doesn't filter nearly as bad as the horror stories say..."
"...I figured the Amsoil filter probably would filter better. At best, it is just as good as the K&N. According to the photos it is slightly worse..."
"...For one, there is very little pressure drop across any air filter, and the difference between the best (K&N) and worst (paper) is very small. Yes as total power output increases, air flow increases, and differential pressure would also increase. So a K&N probably does yield some power on higher output race motors where every last ounce of power must be squeezed out. On lower powered street cars, it is probably not much of an improvement over paper. Basically, an air filter is first and foremost a filter, and should be chosen for it's filtration ability. I know after this enlightening experiment, that is exactly how I will select my air filters. Also remember, that this total differential pressure is measured from the atmosphere via the stock Miata air intake tube, airbox, accross the filter, though the test port, about 6 feet of tygon tubing and the manometer and back to the atmosphere. This is not the pressure drop across the filter itself. I may do a quick test with no filter ( I really hate to do it, but might anyway) to get a good estimate of how much is the system itself sans the filter.
Also bear in mind the K&N is cotton gauze, the Racing Beat is a single stage foam type filter, the Jackson Racing and Amsoil are dual stage foam, and the Napa is a paper filter. So cotton gauze does flow more air than foam as claimed. Amsoil is the best foam filter for flow. The foam filters are a real pain in the rump to service (this just my opinion and not fact). For that reason, I will never ever own a foam filter myself. I've owned several K&Ns and they are easier to service. If you are buying a high performance filter for airflow, K&N is tops in this test..."