The previous owner of my 500E put K&N's in, and I've got to tell you that it was scary how much dirt came out of them on the first washing. What I mean is ... it was immediately obvious how much dirt is in the air because of how much these things had in them. Now I know what kind of job filters do do. But it was really scary to think how much is getting through the K&N's into my engine. If you hold them up to the light, you can see straight through the tiny holes in the weave. I doubt that the K&N's trap much more than half the particulate.

I've thought a lot about going back to the regular filters since then. Who wants to spend 1/2 hour cleaning and re-oiling these buggers every 1500miles anyhow?