I've run the stock paper filter when I've got the K&N filter drying after a cleaning. On the same run from the house to the next town down the valley and back (about 90 kms), I don't record any difference in mileage. Performance gain can be measured only with a dyno. And if I consider the number of kms I drive when the filter is nearing a cleaning I'll bet I'm using more gas as the engine is trying to suck through a muddy gooey mess rather than a dry filter.

I think they are over rated. Also cleaning the oily mess every 10,000 kilometres (I drive in dirt) is no fun. My mechanic also said they will let more dust through than stock. But it's almost irrelavent as the particle size either one lets through is so small (<20 micron?) that, if you change your oil regularly, it has no impact on the motor

So I've gone back to the stock filter. I can also buy 5 of these for the price I paid for the K&N...7 if you count the K&N cleaning kits. By my calculations thats about 100,000 kilometres.

I dunno. It's like wearing a ball cap with the Nike slash on the front. It'll still block the sun without the logo.