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Thread: 89 octane in a 496

  1. #1
    dunaholic
    So I am running a stock 496 mag in my boat (I know what some are going to say, so save your comments please) and was wondering if I really need to run 91 or is 89 sufficient.

  2. #2
    spectras only
    Run what mercruiser recommends for your engine in the manual . They recommend 87 for the 377 [ 6.2 ]and that's what I put in mine . Can't tell the difference when I tried higher octane . The computer is calibrated by the factory , and unless you reflash it ,you're wasting money putting higher than the recommended octane.

  3. #3
    JB in so cal
    I've never run anything but 87 in my HO. No problemo.

  4. #4
    Benjhamina
    I was thinking about this on the way into work this AM. I run a 496 HO and always use 91 but I am not sure I have to. I have heard if it isn't knocking your fine.

  5. #5
    yzfrider
    Merc recomends 87 in the 496.

  6. #6
    jbtrailerjim
    I run 87 octane in mine and have never had a problem.

  7. #7
    RiverToysJas
    In nearly 5 years, I've never put anything but 87 in my 496 (except occationally if it's sat a long while). Never an issue. I've been told lowest available is fine.
    RTJas

  8. #8
    YeLLowBoaT
    if it says it needs 87, run 87. All your doing by using 89 or 91 is costing your self more money in fuel.

  9. #9
    lalhc
    I run 89 in my boat

  10. #10
    CornWater
    Won't make a difference on how it runs, but I run 91 just in case it sits for a while. I've already had to rebuild one motor from bad/stale gas and don't want to go throught that again.

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