Higher octane means the gas has a better ability to resist knocking, which is spurious ignition not caused by the spark plug. Knocking can damage your engine if

Higher octane means the gas has a better ability to resist knocking, which is spurious ignition not caused by the spark plug. Knocking can damage your engine if it happens often. Turbocharged cars have a higher tendency to knock, so they generally need high-octane gas. If you put low-octane in a turbocharged car, most modern engines will detect the knocking and detune the engine automatically to prevent damage, but that means you're not getting the power or efficiency the car was designed for. So use high-octane in turbocharged cars and low octane for non-turbocharged cars. (If you use too high an octane in your car, it won't hurt anything but your wallet.) If you're racing a turbo car you might need close to 100 octane, which cannot easily be bought but it can be made by adding toluene to your gas tank (google it). Other than that check your owner's manual.