Snowmobile Power Valves-Polaris, Ski-Doo, Arctic Cat Variable Exhaust Valve System Basics

You can call it “APV” for Arctic Cat, “RAVE” for Ski-Doo, and “VES” for Polaris. If you own a two-stroke snowmobile manufactured in the last 15 years, the engine may be equipped with a “variable exhaust power valve”. In that case, you probably know that you have to be quite diligent about their cleanliness and operation. This is one engine component that needs to be monitored on a regular basis to maintain best performance.

A variable exhaust power valve is a mobile device located in the exhaust port of an engine. The variation of all brands is to provide the same essential service, which is to vary the height and width of the exhaust port depending on the RPM of the engine. This greatly expands the power band. At low RPM, the valve is in a closed position, promoting more complete combustion. This improves low-end torque and minimizes unburned gas in the exhaust. At high RPM, the valves are wide open for optimum exhaust flow. This allows the engine to spin freely and produce maximum top-end horsepower. Older systems were powered by mechanical linkage that opens and closes valves based on the RPM of the engine. Modern systems are powered by electronic servomotors that accurately position valves throughout the RPM range. Prior to the advent of power valves, engine builders had to determine the size and shape of one of the exhaust ports and pipes. It pre-determined whether the engine would provide optimum output in the high, medium or low RPM range. Power valves allow two-stroke engines to provide horsepower that can be used throughout their operating RPM range.

The latest power valve systems have evolved from many variations over the last 30 years. Yamaha was the first company to succeed in this concept when it integrated a variable exhaust power valve system into a two-stroke Grand Prix road race motorcycle in the late 1970s. Later, this technology was adopted on Yamaha production roads and motocross bikes in the early 1980s. Other motorcycle makers soon came up with their own system. By the early 1990s, virtually all high-performance two-stroke motorcycles, ATVs, personal watercraft and snowmobiles were equipped with a variable exhaust power valve system.

Keeping the power valve system clean is paramount. Since the power valve is located directly in the flow of the exhaust stream, carbon deposits can build up on the valve over time. Accumulation of deposits can change the shape of the valve and change the exhaust flow characteristics of the engine. In extreme cases, the exhaust vents can become completely clogged and costly damage can occur. Sediments can also impede the movement of the valve or leave it stuck in one place. Both of these scenarios significantly impair engine power and power.

The task of maintaining a snowmobile power valve system is not complicated. The service or owner’s manual provides specific instructions on how to remove and clean your system. Be careful when cleaning the valve as you do not want to scratch or roughen the surface. Your manual also provides a specific service interval, which must be adhered to.

Once the valve is clean, there are ways to prevent premature valve buildup. First and foremost, make sure your machine is properly tuned. Excessively abundant carburetor injection is the main cause of this disease. The abundant injection causes excess fuel to flow into the combustion chamber and promotes carbon production. If the threads are fueled, make sure the system is working properly. Also, make sure that the oil injection system is supplying the right amount of oil. Read the spark plugs regularly as described in the manual. If the plug reading is off and you cannot determine the cause, contact your dealer.

Another major factor in power valve deposition is the use of low quality two-stroke oil. Inexpensive basestocks and additives used in low grade oils can be cooked into carbon deposits very quickly. High quality synthetic two-stroke oils are notorious for their clean combustion properties and dramatically reduce the rate of sediment formation. High quality synthetic oils use sophisticated basestock and high temperature additives designed to prevent the buildup of power valves. They also have an effective detergent / dispersant package that allows for much cleaner operation. When it comes to 2-stroke injector oil, you definitely get what you pay for. Spending a little more on oils specially designed to provide clean power valve operation not only improves engine performance, but also saves headaches and costs associated with premature buildup of power valves.

Snowmobiles that operate at low speeds and stable RPMs for long periods of time can also promote sediment accumulation. During this type of operation, the valve remains stationary, which forms deposits. If the position of the valve is constantly changing, it is less likely that deposits will form and grow in size.

Variable exhaust power valves have revolutionized the functionality of two-stroke engines. With a little maintenance and care, it provides trouble-free performance.