Polaris 2001 High-Performance Snowmobile Service Manual (PN 9916690), Page 63Get this manual
ENGINE Variable Exhaust System (V.E.S
Some snowmobiles are equipped with the Polaris Variable Exhaust System (V.E.S This unique exhaust valve management system changes the effective exhaust port height in the cylinder to provide maximum horsepower at high RPM without sacrificing fuel economy and engine torque at low to midrange throttle settingsSpring