I used a K&N on a couple cars about 10 years ago. Here's why I stopped: One day I had the intake tube off and found oily fine grit on the inside of the tube. Same for the leading edges of the throttle plate. Evidently the oil was shedding off the filter, and enough dirt was getting thorough the filter that it was depositing on the items downstream of the filter. Any boost in performance certainly isn't worth shortening the life of my engine and intake sensors.