air filter

[Elliot Cannon]

I've had my 2002 Boxter about a month now and have started doing some service work on it. I just recently replaced the air filter with a paper filter. The old filter I discovered is a K&N. I used K&N on my 914 for 20 years. I will keep the paper filter in for about 4 or 5 thousand miles and replace it with the cleaned a re-oiled K&N. What does the Boxster crowd think of K&N? Some think of it as "overkill". Any thoughts or opinions on this?
Cheers, Elliot

[spinjockey]

General opinion is it can mess up your MAF sensor because of the oil coating.

[JFP in PA]

Use the paper style.

[husker boxster]

A paper filter only lets the smallest particles of dirt thru. Since it stops the vast majority of dirt, that dirt collects on the outside of the filter and will restrict the amt of air that goes thru. That's why you need to replace paper filters often. But you don't let dirt into your engine.

A K&N type filter has holes in the material. It lets more air thru the filter - that's their claim to fame. It will also let more dirt thru. That's why you oil it - the sticky oil catches dirt particles along the edge of the holes. But what if a perfectly sized piece of dirt hits the exact center of the hole? It goes right thru and into your engine. Not good.

The oil dries out and becomes ineffective after a period of time. That allows any particle that would have been caught in the oil to flow right into your engine. Most K&N users spray their filters and then never bother to renew the oil. They're letting gobs of dirt into their engine. Or if they under oil it they will also let extra dirt thru. Not good.

Some K&N owners over oil their filters. When they run their engine, the excess oil is sucked into the intake. On modern cars, chances are the oil will collect on the first interference, the wire in the MAF, coating it and causing it to not function properly. That's when you get a CEL and have to clean your MAF. Not good.

So there's a small window where the K&N filter is working properly and lets more air into your engine, resulting in a miniscule increase in HP. But you're also getting a bit of dirt thru too and chances are the filter is dry and letting lots of dirt in. Is that 5hp worth the damage?

[tcoradeschi]

A K&N will do nothing positive for a stock Boxster.

[S50Sinner]

The K&N won't gain you any power, it'll just make the intake a bit louder and potentially damage your MAF sensor by coating it in oil.

You can achieve the same sound without risking your MAF by cutting the gray foam layer off of a standard paper filter. Use a pair of safety scissors to avoid accidentally cutting through the actual paper. The gray foam is only there for noise insulation and will not affect filter performance.