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Lots of tests have been done recently on the K&N type filters. Yep, they flow slightly better than a paper filter. But ONLY when they're clean! One top engine builder for dirt-track latemodels ran dyno tests, clean K&N and new paper filter were about the same, maybe 3-5HP better for the K&N. BUT- then he stuck on a K&N that had been run in ONE 50-lap race on an average dry racetrack, and due to all the dust that the oil had attracted, the engine was down over 50 horsepower! Granted, that's on an 800HP engine, so it wouldn't kill that much power on a stock engine, but still... If you drive anyplace off the pavement I'd stick with paper. Plus, he said his experience was that the slightly better flow of a clean K&N was due to the fact that it didn't filter as well as paper. Claimed he could tell when he tore a race engine down for a rebuild what kind of filter had been run. The K&N's always showed significantly more wear on the cylinder walls. His thought was that the only good thing K&N has going for them is a very strong marketing program. Best thing you can do air-wise if you want to free up a bit extra power/economy is do like the other post said and free up the ductwork leading to your filter box so the filter can get a good charge of cool air from out in front of the radiator support. Hot underhood air isn't good for performance.
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