Is the K&N air filter worth the money??

[lackskill_imp]

Unless you have characterized the stock air filter with a manometer, you really can't do more than speculate as to the restriction. This doesn't require costly equipment.

FWIW, Cummins once had a note on their European web page indicating NOT to use KnN filters due to poor filtering performance. While they are not EXACTLY the same, OEMs used to use oil wetted metal gauze for their air filters. A GM powertrain engineer told me that poor air filtering was one of the main reasons why 1950s engines had such short engine life. Caveat emptor.

while I agree that you can't do any kind of quantitative analysis without the proper equipment, it is pretty easy to draw a conclusion. For the most part, filtration efficiency and flow rates have an inversely proportional relationship. I'd argue that K&N filters probably flow higher rates that just about any other filter on the market. While on a well worn relatively loose tolerance high mileage car/truck motor, the extra filtration may not be necessary, but I'm guessing (literally, I don't have any tolerance specs at hand) that the clearances on most motorcycle motors is much tighter. But at the same time, if it's a well worn loose tolerance street motor, why do you need incrementally more airflow? More air in means that you need more fuel in as well. Unfortunately, that doesn't always translate to more power.

I'd also wager that if you took multiple identical motors, half with oiled filter media and the other half with paper filter media, and ran them side by side over the life expectancy of the motor that the UOAs would bear much higher wear metal concentrations in the oiled filter media motors. My gut tells me that on motors with lower wear tolerance, that the difference in lifespan would be significant. On motors with higher wear tolerances (such as the aforementioned 4-runner) that this difference would probably never come to light.

Although the application doesn't come close to applying here, this is a pretty good quantitative analysis of several different filters:

http://www.nicoclub.com/archives/kn-vs-oem-filter.html