Fuel Tech

Know what you pour

October 2007 Feature

High performance two-strokes and turboed four-strokes are all the rage in the performance segment of the indus try these days. The faster the better. Horsepower is the name of the game, to make more power, you add a turbo or raise the compression ratio. When you start adjusting the compression and air/fuel ratio, getting a good consistent fuel burn is essential. This is where running the right fuels becomes important.

The main difference in different branded fuels is the consistency of octane and mixture between each batch of fuel that is made. This is especially true with high octane race fuels. When dialing in a snowmobile, each tank of gas should be as close to the last tank as possible. Even the smallest variations in fuel with each tank can cause inconstancies in performance. Buy your race fuel from a reputable source. That should help ensure you get the highest quality race fuel available.

Contrary to popular myths, while there is a reason for higher octane gasoline, it won't necessarily make more horsepower. In a gasoline engine the main issue is heat. You want the combustion chamber to be as cool as possible while still burning all the fuel inside. Get the combustion chamber too hot and detonation will occur which is detrimental to a motor. This is why higher octane fuel is used. It keeps the combustion within safe parameters. Octane doesn't create horsepower; it helps prevent detonation in the high compression engines that do.

It's also a misconception that high octane gasoline and race fuels will make your stock snowmobile run better. Snowmobile engines are designed to run on premium pump gas. Generally speaking, 91 octane is all a stock engine needs. Some engines, like Arctic Cats and Yamaha four-strokes, only require regular unleaded. Most stock and slightly improved engines will run fine on premium unleaded. It's when you start changing compression ratios that you should look into race fuel.

While it is necessary to run a high octane race fuel in a high performance two-stroke motor, not just any race fuel should be used. Refineries make special blends of race fuel for specific engine requirements. For example, Sunoco has a specially formulated race fuel with added lubricity, which will help ensure your 2-stroke motor gets the lubrication it needs to run properly.

Another common misconception is that mixing unleaded 91 octane pump gas with leaded 110 octane race fuel will give you the perfect 100 octane mixture to run in your sled. Doing the math and mixing it 50/50 seems to make sense, but it isn't quite that simple. Generally speaking, mixing unleaded gasoline and leaded fuel together is not an ideal method. Mixing leaded fuel with an unleaded gas destroys the octane of the leaded fuel. That means your final octane will be lower than you expect it to be, which may lead to problems.

There are many different race fuels on the market, so which one is right for your sled? With the help of Kellerstrass Oil and VP Racing Fuels, we found some facts that might help you decide.


  • 105 octane is a great standard grade of racing fuel. It's used in higher compression race engines with up to 13:1 compression and perfect for any application where cost is a factor.


  • 107 octane is formulated for use in naturally aspirated engines with compression ratios up to 14:1 and works well in 2-strokes and is also a good lower cost alternative.


  • 108 octane is probably the best all-around racing fuel made. It's recommended for compression ratios below 15:1 and satisfies the needs of most modern race engines.


  • VP's MR8 107 octane is for use in 2-stroke applications requiring high-octane values. This fuel is for optimum horsepower and performance.


  • 114 octane is recommended for naturally aspirated engines operating at over 8,000 rpm with compression ratios of 14:1 and over in 4-stroke snowmobiles.


  • VP's C14+ 115 octane is for high rpm engines with compression ratios over 14:1, when additional octane is required for better detonation protection.


  • 118 octane is the fuel used in many open mod race sleds. Ski-Doo's race manual states clearly that the high compression factory race engine found in the open class race sleds requires a 118 octane fuel. This is the stuff they use.


  • VP's MR9 87 octane is designed for 4-stroke applications that can tolerate lower octane values. It makes up to 8 percent more power than standard pump gas.


  • VP's MRX01 98 octane is recommended for 2- and 4-stroke applications. It is excellent for high compression applications. It's clean burning, which leaves intake and exhaust valves virtually free of deposits for maximum airflow and performance.
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