Update. I just drove 100 miles of highway today at 70 mph indicated and saw 2 mpg jump on my computer (23.2 to 25.3). I had been averaging about 23 on the highway for the last few months. I need more time to track change in MPG. There is no additional noise from the K & N replacement filter using the stock air box.

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Mark
06 X3 Silver
97 M3 Black
02 R 1150 RT
Member - BMWMOA, BMWCCA