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High Octane Gas Myth

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Old Fashioned Gas PumpI 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.

(Photo: ella_marie)

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55 Responses to “High Octane Gas Myth”

  1. Jeff says:

    Here’s an idea:

    Drain your tank so that you are running on fumes. Have your wife, girlfriend or significant other fill your tank with either 87, 91, or Jack Daniels for that matter. Make sure they don’t tell you which octane they bought. Repeat the process several times by changing the octane and journal your impression of the results. The drug companies refer to this as eliminating the placebo effect. Your answer will be very clear.

  2. Nate says:

    I drive a 2002 dodge neon SXT. I have been keeping a close eye on the prices and I am almost anal about getting the best mileage. When I ran 87 in my car, I would get about 23 MPG (I have a slight lead foot). Then I switched to 93 octane (did not change driving) and I noticed 2 things: 1. More mileage (29.17mpg), and 2. More zoom. I worked out the math using local prices: 3.02 per gallon for 87 and 3.22 for 93. after doing calculations, i found that the cost per mile with 87 (0.13) is 2 cents MORE than 93 (0.11). It’s not much, but a penny saved is a penny earned….

    To add to that, I buy my gas at a wholesale club, so I pay the normal 87 price for 93, which brings my cost to 10 cents per mile.

    I’m going to stay with the 93. Especially because I have a few performance parts on my car.

    -Nate
    Livonia, NY

  3. Janlynn says:

    I have a 1990 240sx and I usually put 87 in it and this time I put 89 in it and it started ticking did I put the wrong gas?

  4. Geoffrey of Bordentown says:

    The octane you should be using, is specified in its user manual, if you did not change your car’s equipment. If you purchased a car designed to run high octane fuel then you darn well need to run high octane fuel. Otherwise stop buying cars with high octane fuel. Ask yourself why did you buy a car that requires premium fuel if you are wondering whether you should follow the instructions on the fuel door and on the instrument cluster and in the user manual of the thing you purchased.

    Now, the user manual written by your car’s manufacturer is no longer the expert on your car if you have modified the equipment on your car. Your manufacturer does not know what you did to your car, and thus your manual is no longer appropriate to follow. You are in uncharted territory.

    If you have modified your car, the responsibility is yours alone, and your tuner’s, to chart the needs of the car, according to a test lab equipped with a dynamometer at a minimum, and possibly auxiliary knock sensors and most certainly an ECU datalogger which can read the knock feedback correction activity within the engine computer while the car is evaluated on the test bed.

    So, heck yes, the dynamometer and the datalogger and the knock sensor will demonstrate that your specially prepared car needs or does not need more octane — typically it DOES require high octane on a performance-modified car. Test your car in a lab. Listen to your car. Read the numbers. Do what the numbers tell you to do. If you don’t understand the numbers then you have no business touching your car’s equipment. If you understand what I am saying then you don’t even need my advice.

    Otherwise you have no business doing anything with a car’s equipment.

    If you do not change the car’s equipment, your manufacturer’s manual is THE authoritative source.

    Many of the earlier comments in this thread are very accurate. Can you guess which ones? Otherwise, don’t plan to keep your car for a long time, sell it while you can, because its engine and probably the other parts will be a pile of crap after you are done with it. Happens all the time. Not that everybody cares what they drive. Some people are just happy as pigs in crap.

  5. utube david blumes says:

    you can mix alcohol with gas this will increase your octane most race cars use 100% japan used it for all there feul in ww2 check it out on utube

  6. 2000 suzuki 2m 125 says:

    my dirtbike manuel says to run a min of 90 octane and i dont think the previous owner was running more tha 87 in it coud that have had an effect on my engie

  7. john says:

    hi! I have a 2007 Toyota Corolla LE and was wondering if 91 octane would be okay to use. thanks

  8. steve says:

    I just bought a new corvette ZO6 with the 7.0 aluminum engine. GM advises use of 91-93 octane fuel with no alcohol. They stress the no alcohol and I think Missouri passed a bill that ALL grades of fuel be 10% methanol, not sure if it is in effect yet. Why the big deal about avoiding alcohol & what happens when I buy the stuff with 10% methanol(be it now or later when it becomes law)????? Where & what kind of gas should I buy. My head is spinning with ideas but don’t want to hurt my car. Have been using BP 92 octane but it is still under 500 miles I want what is best for the long haul. Bring on the opinions guys.

    • TransAM says:

      once the car encounters some problems that a mechanic can determine as being related to the 10% junk we have to use in Missouri then I suggest sending the bill to the state capitol and keep hounding them.. who knows maybe enough complaints could make them repeal their terrible ideas.. just a thought oh and incase you still have that wicked ride congrats, vettes are my favorite :)

  9. thomas says:

    i can never get this straight. Does a higher octane mean that your car will drive further?

  10. sheep. in every car ive ever driven 93 octane has returned better driveability (more torque) better mpg and smoother engine performance these are normal everyday vehicles like cars to trucks to sporty cars with truck engines from 82 tbi gran marqis to 91 mpfi century to 89 240sx mpfi to 95mpfi contuor to 86 tbi century 79 f100 carburated my latest experiment was to run a tbi (throttle body injection) car on 87 91 93 91w/ethonol 93w/ethonol all on seperate tank fulls this was to prove to someone 93 is king of the street gasses the car is equipped with a cold air intake and a cherry bomb resonator for a muffler it had a deeper sound, got better mpgs and had more tq with 93 than all others .does any one know an engine that is quieter is more efficiant than a loud one think little fire cracker next to a stick of dynamite there nuff said dont be sheep be wolves awooo

  11. aua868s says:

    my friends waste a ton of money for this “premium” variety….never bothered to look it up so far….thanks for the info.

    • its not wasting. read what i wrote. baaaaaaa says you lol,

      • premium for ponies says:

        aua868s who cares what your friends do (the right thing btw), premium burns the most efficient, just try to run regular in anything with some compression!

        p.s. I run premium in my 96 mazda millenia, 66 mustang, and 69 cadillac!

    • the cherry bomb only quiets low sounds for you who dont know so the cherry bombs deeper sound was caused by the bigger bang of the 93 . fuels with ethanol produce a higher pitch much louder note, little bang the ethanol had less energy hence the higher louder bang, get it? i hope so teaching is hard the cherry bomb only quiets low sounds for you who dont know. good luck scratching your watch and checking your lol

  12. i refuse to buy new says:

    ethanol vaporizes easily yes cools easily yes but vaporization is caused by engine heat air heat and the act of compression in the cylinder this bleeds off octane points from your fuel and decreases your (octane/energy yield) at the point of combustion and thats no good its making your engine give say 15% gas but with 25% thottle opening no good again can you say lean?!lean temps are way hotter than stoich temps and damage every thing so while your cyls are being cooled thier also being super heated in very fast succesion this is a heat cycle if you want to learn more heat a glass with a blowtorch then cool it with water if you do it right it should spider crack like so many cylinder heads be careful awooo

  13. Eeeeek says:

    Oh My thats all i have to say, the original author did a fairly good job of describing the issues and the differences. Although they may have missed some minor details they did good job for a novice of automotive care.

    What came after words in the comments can only be described as Idiocy. Mr. Bitter nailed down most of the salient points and got kicked by someone that if he is an engine builder would never ever build an engine for me or anyone i know. just because u grow up in the field doesn’t mean u know anything.

    again like others have said its in your owners manual for a reason read it and follow it. i drive a vehicle that gets 11-12 of 87 owners manual recommends 91. Now i use 91 all the time and get 17mpg and before they added ethanol to the gas (which should never be mixed with gasoline) i got 19 to 20 sometimes better.

    theres lots of reasons why ethanol shouldn’t be mixed with gasoline but 2 reasons are it doesn’t stay in solution with gas and it attracts water.

    water in fuel is a bad thing (water injection is a completely different ball of wax and the water isn’t in the fuel.

    anyway read your owners manual see what it recommends then test if u see no difference and the math doesn’t work out then stay with regular for those of us where the math works keep using premium. i wont tell u what to use and not to use but i will say TEST. run full tanks all the way empty and keep track of mileage. thats the best test

    A lot of the newer engines will run on any thing and not ping unless they have After-market parts but this is because of the engine adding more fuel (decreasing mileage) and retarding timing (decreasing mileage). and sometimes your computer cant adjust enough and u will still ping i have heard it in my truck. but just because u can run something does not mean u should or that it is best to do that. please please read your owners manual and do what it recommends or at least test and see what your results are.

  14. oh my is right genius = weird ya cant help it or stop it oh my lol dork

  15. TransAM says:

    Some cars have a specific octane that they need to run through the car.. failing to do so will resault in a knock which isnt good obviously.. if someone is too cheap or doesn’t care about the future owner(s) of the car to buy their recommended octane then so be it. Otherwise buy a handheld tuner and change the settings on the car to make up for the cheaper gas… The brand also counts, in my area all we have is phillips 66 and its quality is shakey. The town I was at before had shell and the 91 v power made my car run so much better you could see it through mpg increase and feel it through the performance.

  16. Guy says:

    how can octane be based on percentage, and you can buy racing gas that’s a 103 octane rating, or higher?

  17. RaT says:

    Octane RATING is calculated not on how much octane a fuel has, but on the percentage of how the fuel performs, as though it were composed of that percentage of octane…capiche? There are fuels which have a MUCH greater RATING than 110, but have very little actual octane content.

  18. RaT says:

    BTW I own a “family car” which I started using 93 in, mileage has increased significantly. With a 20 cent spread between 87 and 93 (very low percentage in cost diff.) I have decided the mileage is well worth the added 20 cents per gallon. I compute a savings of 4.2 cents per gallon when I tested three tanks in a row of each. Add a little performance and the switch is a no-brainer. The savings is not going to pad my retirement, but sure doesn’t hurt my feelings.

  19. 1999sunfire2.2L says:

    ok i drive an old 1999sunfire2.2L and i live way up north in the cold what im trying to find out is,

    will higher octane fuel in a normal car increase the chance of the car starting in -40degrees Celsius?

    or

    does higher octane fuel freeze at a different temperature than lower octane?, im pretty sure there is a difference in freezing temperature but is the difference enough to actually pay extra for just more start up reliability in the cold?

  20. 1999sunfire2.2L says:

    o yea i forgot to mention i have tried a tank of the highest octane fuel i can get at a normal gas station and compared to my usual the lowest octane i didn’t see a difference worth paying more for not even in fuel economy the gas burned no different than cheap gas but that was in the summer time so the car had no chance of freezing

  21. TonyMac says:

    “…that helped create over $10B in 4th quarter profits for companies like Exxon-Mobil.” Quit your whining Wang. Where were your tears when oil was 20/barrel and oil companies were the worst investments in the world. I dig 100 oil, because I invest in oil. I got 200k in XL. The reason Exxon/Moblie is killing is because liberals have choked off the supply of oil and voila — supply and demand take over.

    Actually, your newer, smaller engines are more likely to take high octane than older bigger engines. WHY??? Because of the higher compression of these small engines, as we ask small engines to produce a boat load of power. We now take overhead cams for granted, and four valves per cylinder is normal. No so a few years ago.

  22. ipo says:

    Wang, you should stick to software writing instead of writing silly articles on topics you can barely scratch the surface of. I know by experience that my cars performed much better on premium gas, even though I know why, I don’t have to because the difference is obvious behind the wheel.


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