European specification M156 air box tops improve the breathing of your engine for added power across the entire rev range. European air box tops have a superior design intake horn as well as the omission of the restrictive pre filter, lowering intake air restriction and allowing the engine to produce more power. These air box tops are great addition to any level of tuning, providing an 8 hp gain on a stock motor. European air boxes are complete with new Mass Air Flow Sensors. Installation is quick and simple with no need for any ECU tuning.