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Thread: Octane rating vs. fuel mileage which is best?

  1. #51
    Senior Member stevedmc's Avatar
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    Quote Originally Posted by Eggman View Post
    I filled up with 89 octane once and saw no difference in operation.

    I know of no process or method these cars use to detect octane levels in a tank of gas.
    What happens is the vehicle isn't able to burn off the extra energy and extra carbon deposits are left behind.

    Just like the Red Line transmission oil, any performance increase a person perceives from anything higher than 87 octain fuel is simply a placebo.

    Comparing mpg between fill ups isn't a true test. Put the car on a dyno and then I'll listen.



  2. #52
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    Most cars now have a knock sensor, if the ecu doesn't see a knock it'll throw now timing. And at v10.5:1 89 is better and the car can throw more timing at the motor. I plan someday to test between 87 and 89 on a dyno
    2018 mirage ES manual

        __________________________________________

        click to view fuel log View my fuel log 2018 Mirage Es 1.2 manual: 41.6 mpg (US) ... 17.7 km/L ... 5.7 L/100 km ... 50.0 mpg (Imp)


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    Fummins (10-07-2021)

  4. #53
    Senior Member Cobrajet's Avatar
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    Quote Originally Posted by Cobrajet View Post
    I just filled my car up with 92 octane E0. Will let everyone know if I see a huge difference.Attachment 12272
    Drove nearly 100 miles today under what are 'normal conditions' for this car, and saw what is usually 43.5-44.0 mpg spike up to an even 48.0. I could definitely feel the difference in the gas pedal. Car felt quite a bit snappier, especially on launch. I found myself using less throttle and not needing to hold gears as long. How much of that is 92 octane-vs-E0 is anyone's guess, but I am sure it is probably some intensely complex combination of the two. I won't know until Friday or Saturday when I fill it up again if this nearly 10% difference holds across the entire tank .

    This same station had 87 octane E10 for $3.14 a gallon. This 92 octane E0 was $3.59 a gallon, so the E0 would cost an extra $4.19 for a full tank versus a tank of the E10. Lets say I got an even 4.0 mpg better economy with the E0 over an entire 9.2 gallon tank. That would get me an extra 36.8 miles on a full tank of the high-octane, ethanol-free stuff versus the E10.

    At $3.14 a gallon and 44.0 mpg, I would use an extra $2.62 worth of the E10 to cover that 36.8 miles. $4.19-$2.62 = an extra $1.57 per tank.

    The math doesn't quite pencil out, but it's damned close! Maybe close enough given the noticeable increase in driveability. This station also has 87 octane E0...but they were out of it. I may just try that next.
    Last edited by Cobrajet; 08-06-2018 at 08:46 AM.

  5. #54
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    Quote Originally Posted by stevedmc View Post
    What happens is the vehicle isn't able to burn off the extra energy and extra carbon deposits are left behind.

    Just like the Red Line transmission oil, any performance increase a person perceives from anything higher than 87 octain fuel is simply a placebo.

    Comparing mpg between fill ups isn't a true test. Put the car on a dyno and then I'll listen.
    My 1.0L has 11.5 : 1 compression ratio and in this part of the world they sell 95 octane fuel, which accounts for about 99% sales.
    They also do sell higher octane fuel (98 rated) but it's only for crazy freaks because of extremely elevated (20-25%) prices.

  6. #55
    Quote Originally Posted by foama View Post
    My 1.0L has 11.5 : 1 compression ratio and in this part of the world they sell 95 octane fuel, which accounts for about 99% sales.
    They also do sell higher octane fuel (98 rated) but it's only for crazy freaks because of extremely elevated (20-25%) prices.
    Did you have problems with your car in the past with carbon build up on the valves? Caused by too high of octane???
    Mirage videos:

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage SE wussie cvt edition. 1.2 automatic: 37.7 mpg (US) ... 16.0 km/L ... 6.2 L/100 km ... 45.3 mpg (Imp)


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    Quote Originally Posted by Fummins View Post
    Did you have problems with your car in the past with carbon build up on the valves? Caused by too high of octane???
    I did start a thread about a freak incident when my and several other identical cars would not start because of massive gunk and carbon build-up on the valve stems, which prevented the valves from closing. A car with half open valves will not start. That thread has been updated a few times since. The cause definitely was not too high octane fuel. Research has found that my and the other affected cars were all filled-up at two specific fuel stations. I assume the tank truck contaminated the fuel with whatever substance else.


    After that incident, I bought a USB endoscope camera, and regularly looked at and photographed the valves and combustion chambers. They are and have been perfectly clean ever since. All fuel sold in this state is supposedly compliant with what you could call "top tier" if it were in the US.

    Btw, if you want to endoscope the combustion chambers, you could remove the injectors and simply insert the endoscope there.
    Last edited by foama; 08-07-2018 at 06:06 PM.

  8. #57
    Moderator Eggman's Avatar
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    Quote Originally Posted by foama View Post
    Btw, if you want to endoscope the combustion chambers, you could remove the injectors and simply insert the endoscope there.
    I didn't know the injectors had direct access to the combustion chambers. I thought about using the spark plug port for this.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


  9. #58
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    The injectors are right in front of the valves, and their spray cleans them. Access for the endoscope through the injector holes is ideal for looking at the valves. With some fiddling you can see into the combustion chamber. If you just want to see into the combustion chambers and not look at the valves, removing the plugs will do.


    Last edited by foama; 08-07-2018 at 06:22 PM.

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