One of the easiest and best ways to upgrade the breathing abilities of the F2x N55-powered M135i / M235i is with a replacement performance panel air filter. We've developed our own range of MMR performance cotton gauze filters that easily drop into the OE airbox which provide excellent filtration properties, combined with instant performance increases and induction noise enhancements. FEATURES Increased engine performance Improved induction noise Designed to be used with the OE air filter housing Easily fitted and completely washable. Once fitted this product will last the lifetime of your engine