I ran a K&N air filter on my truck for years. I first installed it when I was in my mid-20’s and didn’t know much, and all I was after was more power in my anemic 3VZE engine.
But after rebuilding the top end (2003) due to a blown head gasket, and a later more minor overhaul (2011), each time I was shocked by the amount of of oily dirt coating the entire intake system. I can’t blame a malfunctioning PCV because I tend to replace wear parts approximately twice as often as recommended (this is my low-yearly-mile baby – rocks are rough enough).
Somewhere along the way, I also got interested in oil and oil filters, and started reading Bob Is The Oil Guy. Discussions on the site often focus around oil longevity, oil’s contaminate-carrying capacity, and filtration. But I also saw references to similar themes in air filtration.
Which led to me reading items like this, comparing various air filtration technologies and manufacturers.
And repeatedly, yes, K&N was measured as less restrictive. But it passes huge amounts of dirt, and oil. After tearing into my engine multiple times over the decade that I had the K&N installed, I can believe this.
The K&N went into the trash. It might make sense on a race car where you intend to rebuild the engine every couple races anyway. But if you care about any durability at all, it’s garbage.
There are better ways to get power.
I now run high quality paper filters (usually OEM, AC Delco, or perhaps Mann). Buy them in bulk from Rock Auto; they’re inexpensive.
Any of the following gave me a bigger kick-in-the-pants than the K&N:
Someday I’ll get around to the engine swap. And you can bet your ass I’ll run a Denso or AC Delco paper filter on it.