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What Should I Choose? Explaining Octane Ratings

No matter what kind of engine your vehicle has it will require the right fuel to work properly. When you get to the pumps though there are often three or four different fuels with names like “Regular”, “Premium” and “Plus”. The reason these fuels have these names is because of their octane rating. They should also be marked with a number between 87 and 91. The octane rating is simply how compatible a grade of gasoline is with a particular engine. After you add fuel to your gas tank and get on the go the gasoline is compressed with air in the combustion chamber of your engine. When the pressure reaches a certain point it can cause the gas to spontaneously combust and you hear a “knocking” sound. That’s what you don’t want to happen. This is what is known as an uncontrolled combustion and it happens more often when you use a low octane fuel with a car that has a high performance engine.

When this happens it causes the gas to combust prematurely and knock the piston down while it’s being pushed up by the crank shaft. This is what causes the pinging/knocking. The sound is the metal components of the engine banging together when they shouldn’t. As you might expect this can lead to costly damage and repairs.

If you have a lower octane car, such as an 87, then it’s wrong to assume that you’ll be giving more power to your engine if you use a premium 91-rated fuel. The engine synthesizes the 91-rating fuel with the fuel system as effectively as it synthesizes 87-rated fuel. Octane ratings really matter if you’re driving high-performance vehicle. Such a vehicle will have an engine with a higher compression ratio. As such it needs gasoline that has a higher octane rating to stop premature combustion and damage to the engine.

These higher grades of gasoline are less likely to auto-ignite and can also withstand higher rises in temperature during compression in an internal combustion engine without auto-igniting. As such you won’t hear the knocking sound caused by the kind of uncontrolled combustion you would get with a lower rated gasoline than should be used with your vehicle. These higher rated fuels make ensure that the combustion process only happens when it should and that the engine maintains its integrity as you use it.

The bottom line is your vehicle will have a recommended octane rating and that you, as a sensible car owner, must only ever put fuel with that octane rating at least in your vehicle. If you use a lower octane fuel than recommended then it can damage the engine. Of course carbon will always build up on your valves, pistons, fuel injectors and the like no matter the grade of gasoline used. You should have your fuel system checked and cleaned regularly to ensure that it stays efficient and that your car has good fuel economy.


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