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

  1. #11
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    the fast-trac here in downtown ithaca offers ethanol free 93 octane, i wonder if the fact of no ethanol alone would make a difference.


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        click to view fuel log View my fuel log 2014 Mirage es 1.2 manual: 43.7 mpg (US) ... 18.6 km/L ... 5.4 L/100 km ... 52.5 mpg (Imp)


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    Quote Originally Posted by btavish View Post
    the fast-trac here in downtown ithaca offers ethanol free 93 octane, i wonder if the fact of no ethanol alone would make a difference.

    My wife and I performed a test on her 2012 Honda Civic this last March on our honeymoon. We know what her car does as far as fuel economy on 10% ethanol 87 octane. It routinely gets 39 mpg highway with as high as 45 mpg with me really trying. After filling up with non-ethanol 87 octane in Hot Springs Arkansas, we took off on the highway. When we filled up with gas, we got an average of 48 mpg!!

    Non-ethanol fuel has a higher BTU content so you will always get better fuel economy from non-ethanol fuel than fuel with ethanol in it. So, if you can find 87 octane, non-ethanol then you'll see a nice increase in fuel economy.
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  3. #13
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    Awesome news! will test it out next fill up.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage es 1.2 manual: 43.7 mpg (US) ... 18.6 km/L ... 5.4 L/100 km ... 52.5 mpg (Imp)


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    The engine in these isn't higher compression - unless you're lugging it a lot (and they are geared pretty short - that's not easy) and it is pulling timing, higher octane won't help too much.

    Ethanol free gas would definitely help. Higher octane may help a bit - most modern engines and computers can take advantage a bit ... but not a lot. Now, if we're talking a higher compression engine with DI , absolutely!

    I tried the ethanol free 91 from Fastrac in my Cherokee. Results were bad. The 10% Ethanol gas 87 Octane does hurt mileage compared to 87 Octane straight gas, but I think my old tractor engine just can't do 91 octane.

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    Quote Originally Posted by M-88 View Post
    The engine in these isn't higher compression - unless you're lugging it a lot (and they are geared pretty short - that's not easy) and it is pulling timing, higher octane won't help too much.

    Ethanol free gas would definitely help. Higher octane may help a bit - most modern engines and computers can take advantage a bit ... but not a lot. Now, if we're talking a higher compression engine with DI , absolutely!

    I tried the ethanol free 91 from Fastrac in my Cherokee. Results were bad. The 10% Ethanol gas 87 Octane does hurt mileage compared to 87 Octane straight gas, but I think my old tractor engine just can't do 91 octane.

    The Mirage engine has 10.5:1 compression which is relatively high for a non-direct injection engine. My Chevy Colorado for comparison had 10.0:1 compression and had large gains when running premium. Your Jeep for comparison has no more than 8.8:1 compression. The ONLY way premium gas would help you in this case is if you either advanced your timing, a lot or you ran some kind of forced induction.
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    Alright, I have some preliminary numbers here.

    With 93 octane, 100% highway driving, speeds between 65 - 70 mph, the car averaged 42.9 mpg. However, my wife was in the passenger seat, we had the A/C cranking the entire time, we ran into a lot of rain during the trip so headlights were on and windshield wipers were used, and I had nine 15 watt solar panels in the trunk!

    With 89 octane fuel and the same circumstances above, the car averaged 44.1 mpg.


    I have not had a chance to try 87 octane on the highway yet. But so far, it does not appear that higher octane fuel, on the highway, is helping. In city driving it could be different.


    More updates to come........
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    Quote Originally Posted by 91cavgt View Post
    The Mirage engine has 10.5:1 compression which is relatively high for a non-direct injection engine. My Chevy Colorado for comparison had 10.0:1 compression and had large gains when running premium. Your Jeep for comparison has no more than 8.8:1 compression. The ONLY way premium gas would help you in this case is if you either advanced your timing, a lot or you ran some kind of forced induction.
    Are they that high? That's definitely on the high end for port injected engines - There would be an advantage of running premium then! I could see it pulling timing on hot days.

    My Focus has 10:1 compression - would like to play around with premium fuel and see what it does with the advance.

    The Chrysler ECUs of that era aren't really able to be modified much - so telling it to advance the timing isn't going to happen. If I could find non ethanol 87 ...

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    Again though, do the math: how much more $ are you paying for no-ethanol or 93oct gas vs miles you're getting.

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    Quote Originally Posted by Ares View Post
    Again though, do the math: how much more $ are you paying for no-ethanol or 93oct gas vs miles you're getting.

    When my wife and I did the experiment with running 87 octane "pure gas" in her Civic, the extra $0.40 a gallon ended up being worth it, and cheaper in the long run then running 87 octane fuel with ethanol. Unfortunately, there are no gas stations around here that sell fuel without ethanol. The closest gas station is about 200 miles away!!
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    Quote Originally Posted by Ares View Post
    Again though, do the math: how much more $ are you paying for no-ethanol or 93oct gas vs miles you're getting.
    I have to post it up on a few other forums still with a bit more detail, but my parents came to where I live twice over the weekend. Their vehicle is a 2014 Ecoboost Escape (2.0L). They went through 3/4 tank of gas both days - and I had them fill up with 93 for the second day - it should have been around 90 or 91 by the time everything is done and mixed in.

    It's a good mix of highway and city driving.

    Sunday MPG: 25.3 - 87 Octane, mid 70s (no A/C). Noticed that the vehicle did have to shift down out of OD on some small hills.
    Monday MPG: 29.0 - 91 Octane, mid 80s (Max A/C). Vehicle did not have to shift down as much on smaller hills.



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