Filling Up at the Pump: Octane Ratings Explained

Finally understand your car with these octane ratings explained.

Finally understand your car with these octane ratings explained.

Getting gas is one of the most routine things you can do with a car. Simply stop at the pump, select the octane, and fill it up. But do you know what the octane rating means? Read on to see octane ratings explained.

What is an octane rating? According to How Stuff Works, octane represents the fuel’s ability to be compressed before exploding. Car engines are almost always four-stroke engines, which means the pistons go through four different stages, including the compression stage. At gasoline is mixed with air, it is then compressed and ignited to provide power.

What happens if you use the wrong octane? Most cars use gasoline with an 87 octane rating, though high-performance engines may require higher ratings. Using a lower octane than required can cause engine misfires, or knocking. Theoretically, switching to high-octane fuel increases compression, therefore increasing horsepower.

There are generally three ratings to select at the pump: 87, 89, and 91/93. Diesel engines don’t need high-octane fuel. They rely on the heat developed from the high-compression to ignite fuel—in other words, they don’t use spark plugs. Therefore, diesel engines actually use fuel that has a low self-ignition point. In a gasoline engine, high-octane fuel (with a high self-ignition point) leads to better performance, but requires ignition (or a spark).

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