Drop in Replacement Air Filters--Good or Bad?

[Gogud]

I have always used foam or gauze air filters in my dirt bikes, street bikes, and cars. Last year at around 100k miles after installing a high flow replacement filter, the MAF on my E36 went bad. When I removed the part and inspected the inside, I noticed the walls were covered with a layer of very fine dust. There was no oil or grime, only dust. I wish I had taken pictures. I set out to find the cause, checking the air boot, all the clamps, the fit of the filter to the housing, and the air box itself. The assembly looked 100% intact from inlet to throttle body. For that entire 100k mile period, a K&N filter was installed and I was happy with it. I checked it at every oil change and cleaned and reoiled it properly, not putting off servicing it until it was heavily clogged. I was in the habit of taking care of filters and did not think it was a hassle. Would there have been the same layer of dust at the same mileage with an OEM filter? I have no way of knowing but suspect it would have been much less. Online research proved interesting. The link to diesel engine air filter tests was most enlightening. The link to bobistheoilguy, though much less rigorous, shows a similar result.

Based on conclusions of both reports, it seems that washable oiled replacement filters provide pracitcally NO horsepower gain and filter poorly. When you consider the percentages, a 10% drop in filtering efficiency with a 'high flow' filter doesn't sound like a significant loss, but when you look at the amount of dirt that passes through over a period of time, it certainly does! If you are going to race and need to squeeze every bit of power out of an engine, go with a high flow or better yet leave out the element entirely for real gains. A screen can be placed over the intake if you are worried about ingesting something large enough to damage the engine. If you are driving on the street and are careful to use the best oil with frequent oil change intervals to make your engine last, it makes about as much sense to install a 'high flow' filter as it does to open the oil filler cap and pour in dirt! I expect this rather harsh conclusion will draw disagreement from intake fans who rely on marketing hype. If you are happy with your intake, good for you. There are many of us looking to invest our limited funds in genuine improvements, not snake oil.

http://duramax-diesel.com/spicer/index.htm

http://www.bobistheoilguy.com/index.php?option=com_content&view=article&id=58&It emid=66

[Canexican]

What a crock. Dude, I'm pretty sure you are in a very extreme minority that feel this way. Just because your E36 crapped out at 100k because of a hypothetically failed filter doesn't prove anything.

There is a reason why people install high flow filters...THEY WORK. If you didn't properly oil it when it needed to be done, well, thats your fault. I've never had a problem and I don't know of anyone that has ever had a problem with a K&N. I know of issues with HKS filters because they don't filter, but K&N would not sell their product and manufacturers wouldn't back it with warranty work if it did not work.

Oh, and your claim that they don't free-up additional power and increase efficiency is like saying that an exhaust doesnt free-up power...it does. K&N dyno tunes every filter for every respective platform before they sell it to the public. My 3000GT's filter was completely OFF for a few thousand miles once and I had no issues. That motor was still purring when I sold the car at 145,000 miles and it always had a K&N filter.

[boostin]

i've had aftermarket filters (AEM/K&N) on my cars since 1999 and as long as you change them every year you're good. you might not even have to do it that often, but i do.

[BMW-driver]

There is a test, somewhere (I'l look it up) between the OEM panelfilter and - around - ten (10) aftermarket panel filters for the 3l.TT engine. conclusion: the paper-OEM gave the best resultst for power. lol.

have fun !
ACS1.35i

[Canexican]

Originally Posted by acs1.35i

There is a test, somewhere (I'l look it up) between the OEM panelfilter and - around - ten (10) aftermarket panel filters for the 3l.TT engine. conclusion: the paper-OEM gave the best resultst for power. lol.

have fun !
ACS1.35i

Even if that is true, it doesnt mean that it applies to all engine platforms. For instance, on my Evo it is easy to get at least 5-10whp more with a K&N Drop-In versus the OEM filter. On the latest Evo X, +15whp is easily attainable. Conclusion: Some OEM filters are better than others, but most of the time a high-flow filter is going to net greater power and fuel efficiency than OEM.

[zamm3k]

Originally Posted by acs1.35i

There is a test, somewhere (I'l look it up) between the OEM panelfilter and - around - ten (10) aftermarket panel filters for the 3l.TT engine. conclusion: the paper-OEM gave the best resultst for power. lol.

have fun !
ACS1.35i

I'm running an AFE dry filter. I put in in with my JB3 and my MPG's went up like CRAZY. I'm pretty sure its mostly due to the filter more than JB3. Therefore, even though I haven't put it on a dyno, better MPG means better airflow, better airflow means more, and easier power.

[WhiteOne]

The way I see it: If a filter keeps more stuff out of my engine then it must offer more restriction. If a filter allows more stuff into my engine it must offer less restriction. I will deal with a small HP loss to keep the bad stuff out. JMHO

[tom @ eas]

Originally Posted by WhiteOne

The way I see it: If a filter keeps more stuff out of my engine then it must offer more restriction. If a filter allows more stuff into my engine it must offer less restriction. I will deal with a small HP loss to keep the bad stuff out. JMHO

A properly oiled-type filter will trap dust particles while still allowing optimum airflow.