Premium Gas Burns Your Wallet
By Tom Catuosco
Purchasing gas for your car, you’re usually offered a choice of three grades of gas - Regular, Mid-Grade, and Premium / Super. Regular gas is the least expensive and Premium is the most expensive. So what do these different grades of gasoline actually mean, and is it worth spending money on the “good stuff”?
How Does Your Car’s Engine Make Power? - To understand the different grades of gas, it’s good to have an understanding of how your car’s engine actually works. Here’s a very basic description. (If you don’t feel like learning something, just skip down to “Is Premium Gas Better Than Regular.”)
The internal combustion engine uses controlled explosions to make power. Inside the engine are cylinders with pistons that move up and down inside the cylinders. The pistons for each different cylinder are all connected to a common crankshaft. At the top of the cylinder, above the piston, is an area called the combustion chamber. A mixture of gas and air is fed into the combustion chamber and compressed by the piston. The tip of a spark plug is also in the combustion chamber.
When a piston is at the top of its stroke (up/down travel inside the cylinder), the spark plug creates a spark which ignites the compressed fuel mixture, causing it to explode inside the chamber. This explosion forces the piston downward, which in turn rotates the crankshaft. All the cylinders fire off at different times to rotate the crankshaft smoothly. The rotating crankshaft is connected via the transmission to the car’s wheels. That’s what makes your car go.
Engine Knock - Ideally, when the spark plug sparks, it ignites the compressed air fuel mixture in the combustion chamber and your car goes vroom. Sometimes the fuel mixture can combust before the spark plug actually ignites it. The combustion chamber is an environment of extreme pressure and heat. This pressure and heat is what can cause the fuel mixture to combust before it should. If combustion occurs at a point in the piston’s stroke other than when it’s supposed to, it interferes with the engine’s proper cycle. This will audibly manifest itself in a pinging or “knocking” sound. Engine knock can be very damaging to your engine.
Octane Ratings - Now that you're versed on the workings of the internal combustion engine, we can talk about what octane means. Regular gas is rated at 87 octane, mid-grade at 89 octane, and premium gas is rated between 91 - 93 octane.
Gasoline is made from oil. Oil is a hydrocarbon fuel, meaning it’s composed of the elements hydrogen and carbon. Gasoline formulations actually contain a couple hundred different hydrocarbons - one of which is “isooctane.” Octane refers to the percentage of isooctane in the gas. Isooctane can deal very well with compression, making it resistant to knocking. The higher the octane rating of gas, the more knock resistant it is.
Is Premium Gas Better Than Regular? - Engine knock is bad, even destructive to car engines. High octane gas is more resistant to engine knock than lower grade gas, so you should always use Premium gas, right?
Most car engines are designed to run on regular 87 octane gas. There is no benefit to using high octane gas on a car designed to run on regular. It’s just a waste of money.
Some cars with higher compression engines, like sports cars, are designed to use premium gas. This is because the higher compression ratio of the engine makes knock a greater possibility if low octane gas is used. If your car requires premium gas, the owner’s manual will specify it. That said, modern high performance engines that are designed for high octane gas also have computer controlled knock sensors. The car’s computer can often make adjustments to the engine and prevent knock even if lower grade fuel is used. So, you’re probably fine if you do use regular octane gas in a high compression engine. The worse that will probably happen is the engine may put out slightly less power and fuel economy may suffer a little.
Bottom Line - For a car designed to run on regular gas, premium is a complete waste of money. For a car that is designed specifically to use premium gas, it’s probably OK to use regular, but your horsepower and MPG may suffer a little. Check with your car’s manufacturer if you’re unsure.