This oil catch can is a must have for any X3, and especially anyone running higher boost pressures. What happens is the more boost you run, the more crank case pressure is created. Your factory crank case vent is routed back into the intake tube. With more crank case pressure and more suction from the turbo, oil will start to be pulled from the bottom end and enter the intake tract. This is not good for sensors, or good to burn the oil from a performance standpoint. Going with our closed loop catch can design will basically eliminate the oil entering your intake.