What's Gasoline Octane?

Have you ever wondered why there are different grades of gasoline? All grades of gasoline have what’s called an octane rating. So what is it and, more importantly, what should you use in your vehicles?

What It Tells You

First of all, the engine in your vehicle burns fuel by compression – in other words, your engine is an internal combustion engine or burns fuel internally. The engine allows a mixture of air and fuel into the combustion area and a piston then compresses this mixture. Your spark plug then ignites this mixture causing an internally explosion that produces the power to run your engine.

Therefore, the octane rating tells you how much the gasoline can be compressed before it ignites spontaneously. Should gasoline ever ignite by compression rather than by the spark plug, then it would cause the engine to knock, possibly damaging your engine (think of it as taking a hammer striking the top part of your piston) – obviously this is not something that’s desirable.

For Example

Take regular gasoline with an 87 octane rating for example. This grade of gasoline would require less compression than gasoline with a 93 octane rating. Simply said, the higher the octane, the more compression it takes before spontaneous combustion occurs. Another way to look at it is that, the higher the octane, the slower the fuel burns, whereas a lower octane rated gasoline burns faster.

Why It Matters

If you use a lower grade of gasoline than what your vehicle manufacturer recommends, then you run the risk of engine damage caused by pinging or pre-detonation. And if you’re using a higher grade of gasoline in an engine that wasn’t originally designed to handle a higher grade, you can actually reduce engine performance and gas mileage. How so? Since the higher grade of gasoline burns slower and you’re using it in an engine that was designed to burn a faster burning fuel, you therefore don’t burn all the fuel. If you don’t burn all the fuel, then all the air that is in the mixture isn’t burned either. Your vehicle computer sees more air in your exhaust system and then compensates by adding more fuel to this perceived lean running condition (more air).

In short, you have more raw fuel being pushed through your exhaust system, causing your catalytic converter(s) to over work and possibly lead to premature failure, not to mention the pollutants released into the air. Unless you’ve had modifications performed to your engine (and computer reprogrammed) to run properly on a higher grade of gasoline, you won’t improve the performance of your vehicle just be buying a better grade of gasoline.

What To Buy

So which grade of gas should you buy? Use the grade that your vehicle manufacturer recommends unless you’ve had your engine modified and your computer reprogrammed to burn a higher grade of gasoline.