High-Octane Gas—Is It Worth It?

American drivers spend billions of dollars per year on premium gas that they don’t even need. These drivers think that because it has higher energy content than normal gas that it also has a higher-octane rating, and many people associate “high-octane” with more efficiency and power. We will explore what octane is and if premium gas is worth the price.

What Exactly is Octane?

Despite what many think, octane doesn’t have anything to do with the quality or energy content. It’s actually the ability of a gasoline to resist engine knock. Additional octane means more knock control.

What Does This Mean for the Driver?

With the exception of a high-performance vehicle, there’s not really any reason to require additional octane. To realize why, we will need to look under the hood and discuss the compression ratio of your engine. The compression ratio refers to the ratio of combustion chamber volume from the largest capacity down to its smallest.

Let’s take, for example, the combustion chamber and cylinder both with 1,000cc of air when at bottom dead center. During the compression stroke, the piston moves up the cylinder, decreasing the volume to something around 100cc. Using the original value and the ending value, we can calculate the compression ratio of this example engine—1000:100 (10:1).

Engine Knock Can Be Damaging to the Pistons

Compressing the air/fuel combination before combustion will increase heat and make the combustion more efficient, which leads to a better running engine. The pressure on the gasoline before it combusts is a balance. If there’s too much pressure, the air & fuel mixture can combust at the wrong time and damage pistons. This is called engine knock.

The majority of stock gas engines have a compression ratio of about 10:1 and will run fine on 87-octane gas. A number of high-performance engines do have higher compression ratios, though. Many of the higher sophistication turbocharged engines have higher compression ratios than those of the past, which helps improve strict requirements when it comes to fuel economy.

It also creates a somewhat new problem referred to as low-speed pre-ignition. The additional pressure in the combustion chamber can lead to ignition of regular gas in an inconsistent manner, leading to engine knock. Higher-octane, premium gas can better deal with higher pressure and can resist engine knock for ideal performance.

Premium Gas Might Not Be the Cleanest Option

A popular misunderstanding of premium gas is that it has a higher amount of cleaning agents and other additives that will enhance performance.

Though many formulators advertise a high-quality premium gasoline, like Shell V-Power Nitro+ or ExxonMobil Synergy, the premium gas available at your local gas station might not be beneficial to performance in any way other than higher octane rating, and even quality can vary.

So Is Premium Gas Worth the Extra Price?

Unless your vehicle needs premium gas or your engine has been modified, buy the cheap gas and save the money.