Here's the passage I was referring to, written by a senior member of Mazda 3 forums about his multiple oil analyses involving a K&N filter. I just wish they posted their UOAs like they do on BITOG.
..."a K&N filter does allow more air to pass through when clean... but also allows more dust/dirt to pass through at the same time (common sense). Not only that, but it also displays how much easier it is to clog than a paper filter (thank the great oiled-cotton for that).
Ever seen a cotton-gauze (K&N) filter under a microscope? No? Here's a good opportunity to see a brand new one under intense magnification:
http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=15;t=000338
I'm not an anti K&N person... but I definitely think that people are gravely mislead into thinking their K&N filter will be "God's gift of power & economy" on their vehicle. The fact is... everytime you wash the K&N filter, you break down the cotton-gauze media even more. 90% of the people out there over-oil them as well... which can cause plenty of problems behind the filter (sure it traps the dirt, but where do you think all that extra oil will go? ).
As for the increase in power & mpg... On my previous vehicle (2000 Nissan Frontier v6), I put a K&N filter in and ran it for 40,000mi. After becoming a bit more educated on the filter by looking at things like what I just showed you, as well as looking at UOA after UOA showing higher silicon signs (most commonly caused by poor air filtration), I took it out and went for a Wix paper filter. The result? The exact same MPG... and no noticable loss in power. After performing my very next UOA... I watched my silicon levels cut in half!
Granted... if you don't keep your vehicle for more than 40-50k miles, I wouldn't worry about it. On the flip side of that however, if you plan on keeping your 3 for longer than that, I would strongly reconsider what you're doing before dropping a K&N in there. Same goes for CAI's & other filtration alterations. Over longer periods of time... that "insignificant" amount of dirt that passes through can turn into a pretty big problem. Why take the risk? To save yourself $50 spread-out over the life of your vehicle? To each their own I suppose..."
