THE MATH OF PUMPING GAS

WHAT THOSE NUMBERS AT THE PUMP REALLY MEAN.

You pull up to the pump and you see the numbers, but what do they mean? Sure, your manufacturer told you which one to use, but you’re still curious as to what’s the difference between 87 and 92 octane. Hopefully, this will help.

Let’s start off with a brief discussion of how gas works in your car. Most cars use four-stroke engines. The compression stroke is where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine compression ratio is 8-to-1.

The gasoline octane rating tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine, which causes damage. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. In order to increase the horsepower of an engine, increase its compression ratio. In other words, the higher compression ratio the higher-octane fuel that is required. This is why they call the “high performance” engines. While higher compression rates mean higher performance and probably a little more fun behind the wheel, the disadvantage is that the gasoline for your engine costs more.

So unless your vehicle manufacturer requests a higher grade of fuel, you probably don’t need it and can save yourself a little money. Then there’s always the matter of preference. If you feel that your vehicle runs better with a higher grade of fuel, then by all means do what feels right to you. Just be sure to check with your vehicle manufacturer.