For Diamond Drive snowmobiles. Uses a torsion spring conversion kit in the secondary for optimum performance. Amazing all-around performance gains. Wicked acceleration. Quicker back-shifting. More efficiently transfers power to the track. Better belt life. Holds RPM much better in deep snow conditions. Adjustable weights to dial in your setup. Adjustable secondary spring tension for those that like to tune. Includes torsion conversion kit, helix, secondary spring, primary spring and Goldstar adjustable magnetic weights. '09 or newer models with electronic engine reverse may have issues going into reverse under heavy load situations. When going into reverse, try to engage the clutch as smoothly as possible..