What is premium gasoline? —Regular versus high octane gas

What is Premium Gasoline? A Comprehensive Guide

The price difference between these regular and premium gasoline is significant, and it begs the question: What is premium gasoline, and why might some vehicles require it? This article delves into the specifics of premium gasoline, explaining its composition, benefits, and the types of engines that demand its use

What is Premium Gasoline?

Premium gasoline has a higher octane rating than regular or mid-grade gasoline. Octane is a measure of a fuel’s ability to resist “knocking” or “pinging.” Knock and ping are different but both can cause significant engine damage over time.

In the United States, regular gasoline typically has an octane rating of 87, mid-grade has a rating of 89, and premium gasoline generally has an octane rating of 91 or higher, with some brands offering 93-octane fuel. In other parts of the world, the octane rating might be measured differently, but the principle remains the same: premium gas is more resistant to knocking.

What is Octane?

A fuel’s octane rating is a numerical value of the fuel’s ability to resist detonation (multiple uncontrolled explosions that occur at the end of the power stroke). Octane is often misunderstood as meaning the fuel has more power. That’s because oil companies advertise their premium fuels as somehow better than regular gasoline. However, a fuel’s octane rating has nothing to do with the fuel’s ability to produce power. A higher octane fuel doesn’t have any more energy content than regular gas and doesn’t provide any more power. It also doesn’t contain any more cleaning additives to fuel than a lower octane gas (that’s a pretty common myth as well and there’s no truth to it). A higher octane rating is only an indication of its ability to resist detonation.

What is detonation?

Let’s review the combustion process in an engine. Air and fuel are combined during the intake stroke. Then, the air/fuel mixture is compressed during the compression stroke. As the piston reaches the top of the compression stroke, the air/fuel mixture is ignited by the spark plug. As the air/fuel mixture begins the burn process, the flame front expands rapidly away from the spark plug, exerting downward pressure on the piston. The rapid pressure rise caused by the expanding flame front raises the temperature of the uncombusted air/fuel mixture to the point where it self-ignites, causing multiple flame fronts in the combustion chamber. When those multiple extremely high-temperature flame fronts collide, they create audible shock waves known as detonation or “knock”. Detonation robs the engine of power and, if allowed to continue, can destroy the engine by cracking or melting the pistons.

The higher octane in premium gasoline octane prevents the pockets of fuel from self-igniting. So it prevents detonation and knock.

Which Engines Require Premium Gasoline And Why

Not all vehicles need premium gasoline, but those that do can benefit significantly from its use. Here’s a look at some scenarios where premium gas is either required or recommended:

• High-Performance Engines— Many sports cars, luxury vehicles, and high-performance models are designed with engines that have higher compression ratios. These engines extract more power from the fuel by compressing it more before ignition. Using lower-octane fuel in these engines can lead to knocking, which reduces performance and can cause engine damage over time. Manufacturers often specify the need for premium gasoline in these vehicles to ensure optimal performance.

• Turbocharged and Supercharged Engines— Vehicles with turbochargers or superchargers compress the air entering the engine, increasing the pressure within the cylinders. This higher pressure can cause lower-octane fuel to ignite prematurely, leading to knocking. Premium gasoline, with its higher resistance to knocking, is often required in these vehicles to prevent damage and maintain efficiency.

So what’s the difference for the ordinary driver?

If your carmaker recommends a 91 or 93 octane fuel, that’s what you should use. If you use a lower octane fuel, like 87, the computer will try to adjust ignition timing to reduce detonation. However, there’s a limit to how much the computer can adjust, so it is possible to get a check engine light if you use 87-octane in your engine, which requires 93-octane.

If your carmaker recommends 87-octane, that’s what you should use. You will gain NO benefit whatsoever by filling up with 91 or 93-octane. That fuel will not provide more power. It does not have added detergents. Although some premium fuels are made without ethanol, that’s not true across the board with all refiners. In other words, filling up with 91 or 93-octane in an engine rated for 87-octane is a complete waste of money.

©, 2021 Rick Muscoplat