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Does anybody know the real difference between the 2 grades of fuel? I have been in the repair field along time and all I know is there is no difference between the two except the octane rating. You ask what is octane rating? Well this is the way the petroleum industry rates the antiknock quality of gasoline, the higher the number on the rating the better the fuel is at stopping engine knock due to predetionation and has nothing to do with fuel economy or engine efficiency.

The reason the manufactures might recommend high octane fuel is because when they designed the motor they could not get the engine to stop predetionation with low octane fuel so they say premium fuel only on the fuel Gage and the gas cap. The difference between the low octane and the higher one is the higher the number is, the slower the fuel burns and this allows for the piston to get to top dead center or the top of it's travel before the fuel ignites pushing the piston down. If the fuel burns to fast as in lower octane fuel the fuel will ignite too soon and as the piston reaches the top of the travel the explosion from fuel will be pushing back at the piston on its way up and a knock is heard.

Regular gas will not knock if the engine was designed for it and the engine is not modified from factory specifications. If you put premium in a car designed for regular the computer of newer cars will advance the ignition and you may get better gas mileage or economy. This is due to the advanced timing and does not make the fuel any better or worse for your car.

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