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Old 09-24-2005, 10:09 PM   #1
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K & N Air Filters?

I heard that K & N air filters can leak oil onto the oxygen sensors,is this true? Niello Porsche in Rocklin said to me that they would not install it because they can not guarentee me it would work correctly without leaking oil. I talked to Performance Porducts and they said the only reason those incidents happened because "some idiots poured ALL of the oil onto the air filters". Anyone here use K & N air filters on the 2.5L engines? If so what is your expierence with them like?

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Old 09-24-2005, 10:51 PM   #2
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The K&N and other oiled cotton gauze filters have been known to contaminate the MAF sensors, not the 0 sensors. Whether too much Oil was used is a possibility. But, there are several other reasons why the K&N Type Filters aren't a good choice.

A couple points which must be made:

A K&N Filter does let in more air, but also more dirt - 18 times more in the test linked below. This stands to reason, because the only way you can let in more air from the same sized Filter is to have bigger holes in it.

And, most stock air filters (if in servicable condition) are already capable of flowing more air (CFM) than the engine can use - about 99% of them. So adding a Filter which provides even more air is redundant.

While there are some Dyno Reports which show a modest HP/Torque increase with K&N and some other Aftermarket Filters, most of these have incorporated the use of the Aftermarket Filter as a compliment to other modifications such as porting, polishing, swapping injectors, ECU Upgrades, Header and Exhaust modifications, so these results are fairly tainted.

Even those very few which show advantages from the Aftermarket Filter alone are misleading. If you look closely at the data, the increases usually exist only very high in the Power Curve, and then usually with a corresponding decrease in the mid-ranges (where you normally drive).

Also, if you look at the test data linked below, pay particular attention to the Time to Restriction Test. This indicates that the K&N became restricted in 1/3 the time of the leading paper filter. This means that in just a few thousand miles, the K&N actually underperforms the Paper Filters and relinquishes any moderate HP gains it may have.

Finally, since most of the dirt which passes through the Filter, any Filter, ends up in your Engine Oil, using a Filter which passes 18 times more dirt means that you have also considerably shortened your Oil Change Interval (if you're interested in preserving your Car's Good Health).

No, there are few difinitive tests (if any) which show the Aftermarket Filters to be superior. But, there are several tests which show how inferior they actually are. One of the best is here: http://home.usadatanet.net/~jbplock/ISO5011/SPICER.htm

This should pretty much end the argument!

Happy Motoring!...Jim'99

Last edited by MNBoxster; 09-25-2005 at 04:33 PM.
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Old 09-25-2005, 02:44 AM   #3
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Yep they do.

I've had a blown short block with my Subaru Impreza GT Turbo on them.
Oil fouled maf sensor, maf sensor fauled ECU reading, ECU puts to less fuel in related to the actual air coming in, lean mixture, knocking, bye bye piston.

DON'T DO IT on MAF based cars like the GTT or Boxster(S). I learned it the hard, $, way.

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Old 09-25-2005, 06:08 AM   #4
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Jim's post is dead on.

Personally, I would not use the K and N in the Box. The filter qualities make it a bad bet for a happy engine. There is no way you will get 15K miles out of the oil with a K and N (IMHO).

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Old 09-25-2005, 06:46 AM   #5
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I'd be scared to use a less restrictive air filter considering the way the Boxster stirs up dust when you drive over it.

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