Don't Pay for Octane You Don't Need

The octane rating of a fuel tells how resistant it is to "knocking" or "pinging". This happens when the fuel-air mixture in your cylinders explodes before the spark tries to set it off. Early explosions that are not timed exactly to the piston position can rob power from your car. High compression pressures in the cylinder are the cause of early explosions, or preignition. The compression pressure is something that is designed into your engine. So you can use the lowest octane that does not cause knocking. Higher octanes do not give you better performance, because the compression pressure of your engine is fixed. This can save on gas money quite a bit!

Tip: you can mix gas of two different octane levels to get what you need. Imagine that your car needs at least 87 octane, and anything lower will cause engine knocking. If your service station has 85 and 89 octane, but no 87 octane, then putting in the 89 octane will keep your engine from knocking, but you are paying the higher price. What you can do is buy half a tank of 85 octane, and then top up the other half with 89 octane. They will mix to give you the 87 octane that your car needs, but you only paid the expensive price on half a tank!