MPG difference between 87 octane and 89 octane?

Discussion in 'Fuel Economy' started by diamondlarry, May 24, 2012.

  1. Motorpsycho Jim

    Motorpsycho Jim smoke drink screw ride

    one difference is i get a little better mpg using the fuel with the higher AKI. per 05 suzuki mc w/11.3:1 CR.
  2. some_other_dave

    some_other_dave Well-Known Member

    Just to contradict myself:

    I did use 87 in the MINI a tank or two ago. It was not on purpose... No adverse effects that I noticed! The MPG went slightly higher (<1 MPG) but it didn't drop. The next tank was back to 91, and the MPG got slightly higher again.

    From this, I conclude that in my car, it made no appreciable difference in fuel economy.

  3. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    I tested 87 vs 93 in my Fit. My thinking was, if there is a difference, the Scangauge should show it in the timing under load. If 87 is knocking under load it'll retard the timing. That should be the difference between the grades, since the number is the Anti Knock Index.

    No difference. At 2000 rpm and 80% load the ignition timing was the same with 87, then with 93, then with 87 again on three consecutive tanks. (it was a few months ago so I don't remember what the timing was, but it was the same)
  4. RedylC94

    RedylC94 Well-Known Member

    That's logical.
  5. Mendel Leisk

    Mendel Leisk 2010 Prius (CAN Touring) Staff Member

    If the experiment was repeated, with a higher compression engine, one spec'd to require higher octane, then you'd maybe see retarded timing with the lower octane.
  6. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    Right. What it tells me is that this engine is designed for 87 and more than that doesn't gain anything.
  7. litesong

    litesong litesong

    An older thread labeled about 87 & 89 octane differences. However, the original post also talked about E0 & the following posts meandered onto many various octanes & also, E10-E0 differences. So in the spirit of this thread, I want to talk about 87 octane 100% ethanol-free gasoline(E0) compared to 87 octane 10% ethanol blends(E10).

    87 octane 100% ethanol-free gasoline(E0) is.....drumroll, please........87 octane, just as the good gasoline engine engineers designed the 87 octane gasoline engine to burn.

    Now, 87 octane 10% ethanol fuel blends(E10) is..... a mix of octanes, the majority of which, the good gasoline engine engineers did NOT design the 87 octane gasoline engine to burn. First, the 10% ethanol has an octane of 114, proudly announced by ethanol advocates, BUT way out of the design parameter of the 87 octane gasoline engine. Second, the remaining 90% of the fuel, in order to balance the ethanol octane, MUST be octane 84!!!! Yes, even this remaining gasoline octane is OUTSIDE the design parameter of the 87 octane gasoline engine!!

    There is an equation to calculate octane of this remaining gasoline, that can be used for upper octane E10 fuels. For example, 93 octane E10: to balance the ethanol, the remaining gasoline octane, isn't 93, but is 90.66!!

    Yeah, the gasoline portion in 87 octane E10 ain't 87 octane, but is 84, & the gasoline portion in 93 octane E10 ain't 93, but 90.66.

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