Here's a thread with all the info on K&N's poor filtration in one place K&N's statement on their filters' ineffectiveness at filtering - AnandTech Forums
Here's a thread where a K&N rep posted some PR
nonsense and got torn apart by members. Science is against K&N-- all they have is marketing and misinformed consumers. http://atforums.mobi/msg.php?threadi...65&STARTPAGE=1
Of course there will be many posts saying things like "I use K&N and I have no problems". Yes, well many people use 5W-20 non-synch oil from Jiffy Lube and have no problems. But enthusiasts like us typically like to use the best product we can. We don't use crappy oils, many of us use 5W-30 for more wear protection, we don't buy awful Chinese tires, we choose the better hoses and belts. So why would we use a filter that lets through 40x as much dirt as the best paper filter? Sorry but "My car works fine with crappy product X" isn't a good argument, especially since the typical driver wouldn't notice the additional wear from bad oil or bad filters.
Most important graph: