REVOLUTIONARY PERFORMANCE Boyesen"s patented dual-stage design incorporates a specially shaped top reed and a ported bottom reed. The top reed is lightweight and resilient for crisp throttle response at partial throttle or low RPMs. The stiffer, bottom reed is ported to provide maximum flow and horsepower at higher RPMs. More valves equals more power by creating: More Air Flow. The dual-stage design allows you to replace your stock reed stop with a Rev-Plate which permits the reeds to open freely and function efficiently. More Air Velocity. The multi-port feature of the bottom reed creates more channels for the charge, delivering increased velocity to the intake ports. More Overall Power. Dual-stage reeds work in unison to perform efficiently throughout the entire powerband. The difference in stiffness between the top reed and the bottom reed allow the reeds to respond quickly and accurately to changes in engine pressure. This translates into quicker acceleration, crisper throttle response and increased horsepower throughout the powerband. Quicker acceleration for that all-important holeshot. Crisper throttle response for fast corner exits and surer jumps. More horsepower throughout the powerband for guaranteed performance. Improved engine efficiency and fuel economy for the long distance rider. Longer life - Boyesen Power Reeds outlast all other aftermarket reeds. Additonal Fitment:1984-1991 ARCTIC CAT 6000 El Tigre1981-1981 SCORPION Sidewinder1978-1988 ARCTIC CAT Spirit440EXTLq. Cooled1978-1988 ARCTIC CAT Spirit340EXTLq. Cooled1985-1988 ARCTIC CAT Spirit530EXTLq. Cooled