Video: A Look at Snowmobile Exhaust Power Valves

Mounted in the exhaust port of many snowmobiles, personal watercraft, and motorcycles, exhaust power valves are devices designed to improve combustion efficiency at varying RPM. Improved efficiency increases horsepower and lowers exhaust emissions. Examples of power valve systems include those used by Yamaha, RAVE by Bombardier, Variable Exhaust System or VES by Polaris, and APV by Arctic Cat.

At low RPM, the valves are in a closed position, which promotes more complete combustion, improves low-end torque and minimizes unburned gasses in the exhaust stream. At high RPM, the valves are in an open position for improved exhaust flow, increasing RPM, combustion efficiency, and horsepower.

Because exhaust power valves are located in the direct stream of exhaust flow, deposits consisting of soot, carbon, and ash quickly accumulate requiring them be cleaned regularly. Otherwise the deposits can cause the valves to stick, and operators will notice horsepower loss and poor operation.

Exhaust Power Valve with Deposit Build-up Clean Exhaust Power Valve

In some instances, the deposit build-up may be worse than others. Machines operated at low speed and steady RPM for extended periods of time will build up deposits faster than machines operated at high speeds and varying RPM. Low speed operation does not actuate the valve, allowing deposits to rapidly form. This is different from higher speed where the valves are actuated often disrupting the deposit formation.

The type of two-cycle oil will also impact valve operation. Exhaust valves get very hot and will quickly cook oils down to hard carbon deposits. AMSOIL INTERCEPTOR Synthetic Two-Cycle Oil contains synthetic base oils and high temperature additives that effectively prevent exhaust power valve sticking. INTERCEPTOR is the result of extensive research conducted in the Rocky Mountain region, where hundreds of units were tested in some of the most extreme operating conditions available.

Two-Cycle engine manufacturers recommend cleaning exhaust valves, and it can be quite difficult if the valves are stuck. In severe cases, extreme force must be used to remove the valve from the cylinder. When cleaning valves, be careful if using aggressive methods such as sand blasting, grinding or scraping. This can cause wear and rough surfaces. Solvent-based cleaners such as AMSOIL Power Foam can help.

AMSOIL INTERCEPTOR is the primary recommendation for engines equipped with exhaust power valves. INTERCEPTOR will significantly extend and greatly ease maintenance. AMSOIL HP Injector and Dominator Synthetic Two-Cycle Racing Oil may also be used with exhaust power valves.