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Fuel and octane rating

So many discussions and legends about the fuel… How many times during a season do we hear stuff like: « I gas up with premium, it is much better!!! »  Myth or reality…?

The octane rating indicates the anti-knock characteristics of the fuel, which means that the higher is the octane rating, the harder is the fuel to explode.  This said, a 2-stroke engine is calibrated in order to use the octane rating fixed by the manufacturer.  Many factors influence the choice: the compression ratio and the ignition advance are the most important. They are themselves determined by the engine revolution, coming from its conception and the exhaust calibration.

So, an engine calibrated for an octane rating of 87 means that with the maximum compression ratio of the engine (top dead center of the piston) and the exact moment when the ignition happens (a few mils before the top dead center), the fuel with an octane rating of 87 will burn completely and that the explosion will be at its maximum power.  In the same engine, if you use an octane rating of 91, the explosion will not be at its maximum power because the compression will not be high enough to correctly burn the fuel-air mixture.  There will then be a loss of fuel not burned, loss of power and a higher fuel consumption.

This loss of power is hardly noticeable, but it is exactly what happens.  Many tests on a dynamometer give evidence of a loss of power with an inadequate octane rating.

Many arguments also concern the additives added by the companies.  The greatest difference between the octane ratings is about the fuel pipe antifreeze ratio that is higher in the premium gas at some retailers.  For example, Petro Canada adds a higher quantity of Tactrol in their fuel with a higher octane rating.

Here is a hunch about the basic function of the octane ratings and their use; each engine is calibrated by the manufacturer and it is good to respect it, for the performances as well as for your wallet.

Have a good season!!!

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