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Will higher octane gas improve MPG

Will higher octane gas improve MPG

In most cases, higher octane gas will not improve performance or MPH

That’s because the ONLY difference between 87 octane and 93 octane is fuel’s ability to resist detonation and knock. That’s it. Premium gas doesn’t contain more energy compared to regular octane fuel. And, unlike the myth, premium fuel does not contain any more cleaning additives than 87 octane fuel.

The only time higher octane gas will improve performance and MPH

The only exception to that statement is if you own a late model car equipped with a knock sensor and your engine has carbon deposits in the combustion chamber. In that case, if the engine has been experiencing pre-ignition (ping) from the carbon deposits or detonation, the knock sensor has been reporting those events to the engine control computer. The computer then retards spark timing to reduce the knock.

If you then add a higher octane fuel and prevent pre-ignition and detonation, the computer will slowly advance ignition timing, which will give you better performance and MPG. But it’s not coming from more energy in the fuel, you’re getting more power because spark timing is back to an optimal level and the higher octane is preventing knock.

What happens when you use 87 octane gas in an engine designed for higher octane gas

If the manufacturer of your high compression engine recommends 93 octane and you fill it with 87, you’re going to get lower gas mileage. You may not hear knocking, but that’s only because the computer is a step ahead of you. The computer senses detonation by way of the knock sensor and retards the spark timing to prevent multiple flame fronts (one started by the detonation or pre-ignition and a second one from the spark plug). Retarding the timing DOES lower your gas mileage. That’s why it’s never a good idea to run lower octane in a high compression engine.

Here’s another myth–different brands of gas give dramatically different MPGs. There are slight differences in gas between brands because gas is a blend of almost 150 different components and each brand uses their own recipe. But the differences are minor–at best 1 MPG. In many urban areas fuel is delivered by pipeline to fuel terminals. All the fuel from that particular terminal is the same. It’s only when the individual trucks from each brand fill up that the additives are poured in. Yes, the additives are different from one brand to the next. But as to the “power” contained in each gallon–it’s all the same. Gas is gas.

If your car starts better on BP than Shell, it’s because the additives work better in your engine. But you can’t make the claim that because it works better in your engine, it will work better in every engine.

What is detonation?

detonation damage to pistons cause by not using high octane gas

Detonation damage to pistons

Detonation is spontaneous combustion in multiple areas of the cylinder after the initial ignition by the spark plug. The multiple flame fronts collide, causing an audible knock. Detonation can damage pistons. For more information on detonation, see this post.

What’s the difference between pre-ignition and detonation?

As the term implies, pre-ignition is fuel ignition BEFORE the spark plug fires. It’s caused by glowing carbon deposits in the cylinder or in high compression engines where the air/fuel mixture is heated so rapidly by compression that it self ignites.

preignitiuon damage

Pre-ignition damage high heat

Detonation happens after the spark plug event, at the bottom of the power stroke. For a fuller explanation, see this post

 

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat



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