I have installed the K&N air filter and I see an increase in gas mileage. Before the change I would see 48-49 MPG on my drive to work. Since the change I see 52-54 MPG. It must be making more power, but I could not quantify how much more. It probably accelerates quicker, but is still not quick. I had an '07 MAZDASPEED 3 before the iA so it seems very slow to me.
I just bought mine and it should be coming in the mail tomorrow. I get about 28-34mpg in city/rural driving with tons of stops, so any more mileage would help, and I am hoping for at least 1 more HP lol. I will let you know my thoughts once I drop it in.
K and N strikes me as a bad idea. I would stick to OEM specs and the manufacturer's recommendations.
Earlier in life, I used to call on garages and fleets to sell a different brand of aftermarket filters - one that was known for better dirt retention and at the cost of reduced flow, sort of an opposite to K and N.
Quote: "I am professional mechanic with over 40 years experience and I can not tell you how many times I have seen excessive dirt in engine intakes only to find a K&N installed instead of a real filter. Sure they flow slightly better but how do you think they do that? Hold one up to a bright light sometime and see how much light comes through those big holes...At a Bosch service school onetime the discussion went to mass air flow failures and K&N filters were mentioned. The instructor said that the K and N stand for "kill it now"