Snowmobiles equipped with detonation sensors, (knock sensors), both two-stroke and four-stroke, automatically compensate for various fuel quality and octane ratings. The ignition timing and...

Snowmobiles equipped with detonation sensors, (knock sensors), both two-stroke and four-stroke, automatically compensate for various fuel quality and octane ratings. The ignition timing and in some cases amount of fuel delivered is varied to avoid damaging detonation. This also means that the engine will make more power when fed higher octane fuel, and less power as the system compensates for lower quality fuel.

For example, the T-660 Turbo Arctic Cat four-stroke will run safely on 87 octane fuel, but will make more power on 92-octane.

On the other hand, four-stroke engines not fitted with knock sensors (like the Yamaha RX-1) that are designed to run safely on 87 octane fuel see little advantage to the use of high octane fuel other than cooler operation. In fact, the power output may be reduced with the higher-octane fuel.

Two-stroke engines not fitted with knock sensors generally benefit from the use of higher-octane fuel as a measure of insurance against detonation, as detonation is typically more damaging to a two-stroke than a four-stroke. Most two-stroke snowmobile engines run fairly high compression levels, thus generally require higher-octane fuels. Some Polaris models feature a two-position key switch that allows the user to manually select a different timing curve, better suited to the use of each fuel type.

How about using lower octane fuels at higher elevations? This is common in the automotive world, as you can find lower octane fuel out in western states (higher elevations) in the 84-85 range. The air density is lower at higher elevations than in the Midwest or eastern areas. This means less air to squeeze during the compression stroke, which also means less heat and pressure in the combustion chamber. Therefore, most engines can safely run a lower-octane fuel at higher elevations. Some riders who run 91-92 in the Midwest safely run 89 out west, and this is also why western riders who ONLY ride at higher elevations can stack on even more compression yet remain safe on pump gas. Yet these same sleds, if brought down in elevation, require an increasingly higher octane fuel.

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