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High octane gas is expensive - Is it worth the money?

In my post Is Cheap Gas Bad for Your Car, I discovered that in the U.S., gas is gas. The only significant difference between cheap gas and brand name gas is the price. But what about octane rating?

  • Does using a higher octane gas improve mileage or fuel economy?
  • Does higher octane gas give my car more power?

The answers may surprise you.

High Octane - Simple Definition

Technically, an octane rating measures the proportion of isooctane to heptane in a fuel. But as a practical matter, a fuel's octane rating relates to how much energy it takes to ignite that fuel.

The higher the octane number, the more energy it takes to ignite the gas.

Does High Octane Gas Improve Gas Mileage?

No. Unless your car is explicitly designed to run on high octane gas1 (it's rare, read your car's manual), using a high octane gas will NOT give your car better mileage. That's because the rating refers to how much energy it takes to ignite the gas, not directly to how much energy the gas puts out.

Does High Octane Gas Give More Power?

No. Unless your car is explicitly designed for high octane gas (see your car's manual), using a high octane gas will NOT improve the power output of your engine. Again, the octane rating relates to how much energy it takes to ignite the gas, but NOT directly to how much energy the gas puts out.

Exception 1 - By Design

One exception is with engines or cars designed for high octane gas. In that case, using high octane gas WILL improve performance and mileage. The reason has to do with the compression and ignition timing characteristics of the engine. Those specially designed engines will only perform efficiently with higher octane gas. Most engines are not designed this way.

Exception 2 - Engine Knocking

The second exception is if your car has a lot of engine knocking or pinging. This is a sign that the gas is not igniting when it should. This reduces the power and efficiency of the engine. Assuming your car's manual says it's okay, using a high octane gas can help. Does High Octane Gas Reduce Engine Knocking?

Yes! If anything, high octane gas will help reduce engine knocking in most cars (assuming your car's manual says it's okay to use such a gas). The reason follows from the fact that octane is related to how much energy is needed to ignite the gas. If the gas ignites too easily, it can ignite before it's suppose to, which causes the engine knocking or pinging sound. Using high octane gas can reduce and even eliminate that knocking, and help your engine run more efficiently.

Conclusion

In most cases there is no reason to use and pay for expensive high octane gas. Unless your car was designed for such gas:

  • High octane gas does NOT improve gas mileage
  • High octane gas does NOT improve power output

Exceptions: If your car is explicitly designed for high octane gas, use it. If your car has engine knocking problems (and your car manual says it's okay), using high octane gas may reduce the knocking.

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sezer — 22 September 2007, 13:31

Ok, mr smart, so why my 94 honda drives about 35 mpg with 89 octane and around 38 mpg with 93?

And all racers are stupid to pay 110 octane gas for racing.

Brent — 22 September 2007, 14:24

Sounds like the your engine likes the higher octane. This is not always the case, at least that's what articles I've read say. If the engine is designed for higher octane, you'll get better mileage. Good to experiment for yourself, as you have done.

186 — 25 February 2008, 13:08

higher octane is best on sealevel humid and hot conditions. at altitude a 87 octane performs as 93 at sealevel.

If low octane is exploding before timing it will not burn right and explode correctly to give all the power it got, thus less power and you have to accelerate more and more gas consumption

Brent — 25 February 2008, 15:16

I didn't realize that about different octanes for different elevations. Very interesting. Thanks for sharing the info.

Matt - Elitedrumr@gmail.com — 24 May 2008, 11:51

Yep, engines that are not designed for high octane gas will actually lose power because it burns so much slower and the ignition timing is not tuned for it.

My car on the other hand, 2.7L Twin Turbo Audi S4, LOVES higher octane gas. Mainly because I can tune the car from my laptop and advance my ignition timing 6 degrees with race gas. The car picks up a ton because it can be tuned for it.

Good article, just wanted to add to the mix and explain how higher octane gas helps "racers" at the track.

Brent — 25 May 2008, 09:21

Excellent point, Matt. Some cars are specifically designed for a particular octane, which makes sense, because the octane affects when the fuel mixture ignites in the compression cycle.