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High Octane Gas Myth

Posted By Jim On 02/02/2006 @ 8:02 am In Cars | 55 Comments

I know a lot of people who believe that higher octane gas is better for your car than lower octane gas, as if the words premium next to the higher ratings actually mean the gasoline is better for your car. It isn’t. If you believe it is, don’t be dismayed, you’ve simply become accustomed to reading the words “premium” next to the label and believing the great marketing machine that helped create over $10B in 4th quarter profits for companies like Exxon-Mobil. The octane rating of gasoline is a measure of how much you can compress the gasoline before it ignites, not how “good” it is.

Cars that require higher octane gas actually need that higher priced gas because the engines compress the fuel more before it ignites it. If you put regular gas in a car that requires premium, the gas will prematurely ignite when it’s being compressed and the engine will give you a knocking sound. This is bad for your car.

Chemists perk up…
For all you burgeoning chemists, gasoline is basically octane and heptane, or hydrocarbon chains that are 8 (octane) or 7 (heptane) carbons long. Octane simply can be compressed better (i.e. without the exploding part, at least at the same levels of pressure) than heptane. An octane rating of 87 means it’s 87% octane.

It’s a “rating”…
The reason why higher octane is more expensive is because it’s harder to refine the gasoline so that it contains more octane. Now let’s add another wrinkle… the octane is actually an octane rating, or it behaves as gasoline with that percentage octane would behave but might not actually have that much octane in it. While that doesn’t really matter, it does mean that the gasoline you use could have a mix of other things in it (still real gas though) to give it properties of a higher octane without actually having more octane. Does it matter? I don’t think so but I write software for a living.

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