Performance Air Filter for BMW 1 Series / 3 Series / X1Precision Induction for the BMW N4x Series: BMC High Flow Filtration Who Its For: Engineered for BMW 1 Series, 3 Series, and X1 owners running the N43, N45, and N46 in line four cylinder powerplants. If you find your E90 or E87 feels a bit breathless during mid range acceleration, this is the first step in correcting that factory bottleneck. The Symptom: The factory intake system on these BMW four bangers is designed with a heavy bias toward sound