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The manual on the 9th 14 calls for 95 octane. The only thing in my area that I can find is 91. Is it safe to use an octane additive?
  • Re: Octane additives

    by » 7 years ago


    Your 91 Octane is fine.
    Read this:

    Research Octane Number (RON)
    The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.

    Motor Octane Number (MON)

    Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.[1] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON. Pump gasoline specifications typically require both a minimum RON and a minimum MON.[citation needed]

    Anti-Knock Index (AKI) or (R+M)/2

    In most countries, including Australia, New Zealand and all of those in Europe,[citation needed] the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2. It may also sometimes be called the Posted Octane Number (PON).
    Difference between RON, MON, and AKI

    Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity,[4] and is not typically published for those countries that use the Anti-Knock Index labelling system.
    See the table in the following section for a comparison.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Octane additives

    by » 7 years ago


    Actual octane rating table

    EURO RON MON US: (R+M)/2 (AKI)
    90 83 86.5
    92 85 88.5
    95 87 91
    96 88 92
    98 90 94
    100 91.5 95.75
    105 95 100

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Octane additives

    by » 7 years ago


    As Roger says...
    Depends on where you live and what they version of octane rating they are quoting. In NZ we quote RON and therefore "91" would NOT be suitable we have to use "95" for 912ULS.
    Where do you live ?

  • Re: Octane additives

    by » 7 years ago


    Jeff lives in Arizona. Our 91 Oct. (AKI rated fuel) also has pump advertised 10% ethanol. That said I have friends that test every single batch of fuel they get over the last 12 years. It is usually
    6-7% and they have only seen 8% a couple of times.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Octane additives

    by » 7 years ago


    Thanks Roger,
    As you say the "91 AKI" will be fine. Our CAA (Equivalent of your FAA) issued a warning here about Rotax and Ethanol fuels but I believe that was for a 15% blend. Rotax does have a limit which I am sure you know off the top of your head.

    I have a Sting S4 composite aircraft and there is a guy in California whom had all sorts of trouble with his composite fuel tank and Ethanol fuel (Richard De Haven Sting flight) so not a Rotax issue but one to be careful of....

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