I remember finding a page (didn't bookmark it) that had some articles on the K&N vs stock. I forgot the car. The guy said that the K&Ns let in more dirt than stock filters. He also said the K&Ns flowed more right after cleaning, but the stock filters worked better within a short period.

Anybody see that page?

Has anyone who put K&Ns in the car seen any dirt/particles upstream of the filters?