BMW Air Filters – things to know about ‘performance filters’
One thing that I cannot explain enough to people is that there is no way in hell you’ll feel a significant change in horsepower in your BMW by switching to a different kind of air filter. The most popular of which is K&N filters, which are more of a screen filter with some foam that utilizes a special oil to help it filter. Your local auto parts store will usually have some sort of demonstration with a ping-pong ball that floats higher over one of these filters when compared to its stock counterpart. That’s all fine and dandy, but the last time I checked, there weren’t any ping-pong balls in my engine bay.
I’ve also seen many graphs when one of these filters are installed, and the car is put on a dynometer with the end result being a gain in horsepower and torque. Before getting all giddy, these ‘gains’ are usually about 3-5 horsepower on an engine that produces over 250hp, giving an end result of about a 1-2% gain from that $65 filter you just bought.  Remember too that dynometers have a certain margin of error that can produce a different result through many tests. With any modification, I want to feel it in my seat. The only way you’ll feel one of these filters in your seat is if you were to put it underneath your butt. (more…)