57mm PAIR System Cylinder Head for 150cc GY6 4-stroke engines. PAIR is an acronym for Pulsed Secondary Air Injection System. It is an emissions control system used to lower HC and CO emissions. It works by allowing air into the exhaust flow. Fits 57mm cylinder bore Intake Port Diameter: 25mm Exhaust Port Diameter: 24mm Emission Control System: Pulsed Secondary Air Injection System(PAIR)Model # 164-208.
