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So which fuel is it?

Discussion in 'Generation 1 Prius Discussion' started by babbles, Jan 31, 2022.

  1. babbles

    babbles Junior Member

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    so the manual says
    Select unleaded gasoline with an Oc- tane Rating of 87 (Research Octane Number 91) or higher
    so which one? my daughter had been putting in 91and I didn't know it and put in 5 gl of 87 last evening, will there be an issue?
     
    #1 babbles, Jan 31, 2022
  2. bisco

    bisco cookie crumbler

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    no issues either way. 87 is all that is needed
     
    #2 bisco, Jan 31, 2022
  3. sam spade 2

    sam spade 2 Senior Member

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    In the US, it is 87.
    In some other countries, the exact same fuel is labeled 91......because the measurement systems are different.
    87 is right.
    91 is overkill.
     
    #3 sam spade 2, Jan 31, 2022
  4. babbles

    babbles Junior Member

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    ah dude! thanks much!
     
    #4 babbles, Jan 31, 2022
  5. ChapmanF

    ChapmanF Senior Member

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    To get a little more of the detail behind it ...

    There are a couple ways of measuring the knock-resistance of a fuel, one that gives you the "research octane number" (R) and one that gives you the "motor octane number" (M).

    At US filling stations, the number that is used in labeling is the average of the two, (R+M) รท 2. That is typically 87 for a "regular" blend, which would have a plain R number around 91 (it follows that its M number is around 83).

    If you were in a country that labels fuel with the straight R number, you would look for 91.

    More here:

    Gasoline explained - octane in depth - U.S. Energy Information Administration (EIA)
     
    #5 ChapmanF, Jan 31, 2022
    ammdb likes this.
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