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

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    Octane rating vs. fuel mileage which is best?

    Over the next several months I'll be testing different octane ratings to determine which is better for over all fuel mileage. I understand that our cars are rated to use 87 octane. However, it has been my experience in the past that cars, like ours, with moderate to higher compression ratios actually do get better fuel economy with higher octane fuel, especially in warmer environments. The big question is if the mileage increase is high enough to warrant the extra cost of the higher octane fuel. I plan to find out.

    So, I'll try 3 tanks of 93 octane, then 3 tanks of 89 octane, then 3 tanks of 87 octane to see which one does the best.


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    Senior Member Donut's Avatar
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    sounds interesting, thx for the project.

    you should mix the order to limit the temperature dependence of fuel economy with advancing summer.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage DE 1.2 manual: 47.8 mpg (US) ... 20.3 km/L ... 4.9 L/100 km ... 57.3 mpg (Imp)


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    Do these have ethanol ? Looking forward to the experiment and its results .

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    Quote Originally Posted by Donut View Post
    sounds interesting, thx for the project.

    you should mix the order to limit the temperature dependence of fuel economy with advancing summer.

    Well, seeing how I am going down for surgery next week, it is going to be sometime in the fall before I get to start doing this.
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    Senior Member Ares's Avatar
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    I've done the math back when I had the mustang... I did see MPG improvement during long hwy road trips, and the butt dyno felt 3-5hp more hp changing gas alone.

    I ended up feeling that the extra $ every tank isn't worth the 'performance' attained. Now, with bolt-on mods and a tune, 93 would make a bigger difference.

    If I were to get SpeedLab's bolt-on parts, I would do 93oct.

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    Quote Originally Posted by cinder View Post
    Do these have ethanol ? Looking forward to the experiment and its results .

    Yes. Where I live, the only fuel that is available is fuel that has 10% ethanol in it.


    Several years ago I did a test between the cheap gas station fuel and the name brand fuel. The test vehicle was a 2006 Chevy Colorado and I was using a Scan Gauge to monitor ignition timing at both idle and at 60 mph with cruise control on while driving down a particular strip of road. I found the cheap gas premium 93 octane is equivalent to the name brand (Shell and Chevron were tested) 87 octane fuel. Because of this testing, I will be using Chevron for all of my testing.
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    Senior Member Charlie's Avatar
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    Quote Originally Posted by 91cavgt View Post
    Yes. Where I live, the only fuel that is available is fuel that has 10% ethanol in it.


    Several years ago I did a test between the cheap gas station fuel and the name brand fuel. The test vehicle was a 2006 Chevy Colorado and I was using a Scan Gauge to monitor ignition timing at both idle and at 60 mph with cruise control on while driving down a particular strip of road. I found the cheap gas premium 93 octane is equivalent to the name brand (Shell and Chevron were tested) 87 octane fuel. Because of this testing, I will be using Chevron for all of my testing.
    Yay, I've used Chevron basically exclusively, even on my old car. Gas is all the same, it's the additives you're placing your bets on. The only gas brands I remember from a list of 'superior additive' packages were Chevron, Mobil, Texaco, 76. There were more, but I can't remember..

    -Charlie-

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    Chevron with Techron . Must be nice .

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    Same here. Been done Chevron or Shell.

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    Alright, I filled up with gas today for the first time. 277 miles and 7.4 gallons total for an average of 37.4 mpg. This tank was 100% city driving and the A/C has been on the entire time. I filled up with 93 octane Chevron gas and tomorrow I'm going on a road trip.

    My first impressions with 93 octane in the tank is the motor seems to be smoother when under a load and at low rpm. With 87 octane, I could feel the ignition timing going up, then being pulled back down quickly when under a load at low rpm. I could feel it as almost like a light jerking feeling. With the 93 octane, the light jerking feeling is completely gone and the car feels smoother upon acceleration. I'm not talking about full throttle acceleration but rather enough throttle input to bring the rpms up to about 2500 rpm. Also, keep in mind that it is hot here. The current temperature is 95 degrees(35 degrees C) with a 72 degree(22.2 degrees C) dew point.


    I will report back tomorrow with the mileage.


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