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  1. #1
    vidbuster's Avatar
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    Above 91 octane, is it bad?

    I've got a trip lined up and I have to fill up with 87. I will be on the water for 3 days and am going to try and sneak on a few 100 octane 5 gal jugs on the boat. I can buy this from a 76 station by my house. I figured I'll throw in about 5 gallons of the 100 when I fill up around 9 or 10 gallons of 87.

    According to my calculation with 10.9 gal of 87 and 5 gal of 100, I'm coming out with 91.8 octane. Although, thats a perfect mix and most likely that won't happen. Because I don't want to run anything other than 91 in my tank and that I've been told NOT to use an octane booster, is it ok if my mix turns out greater than 92 octane? What happens if my mix turns 95 octane?



  2. #2
    800AMSOIL4U's Avatar
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    Higher octane than what is needed for the ski will mean it just might run a little slower. See if you can find 110 it should be quit a bit less $$ for you.

    Octane mixing chart.
    Attached Files Attached Files
    Last edited by 800AMSOIL4U; 06-07-2007 at 02:16 PM.

  3. #3
    Matthew K ReDevilRXP's Avatar
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    My ski has seen nothing but 93 and it runs like a champ from day one. I cant imagine 95 being a big difference but thats just me opinion.

  4. #4
    Speed200's Avatar
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    Yes you'd be fine mixing it like you are saying. If it's a hair under or over you'll still be fine. These motors have knock sensors so if your octane is too low it will pull some timing out and you'll be safe. I wouldn't recommend doing it all the time but for a weekend you'll be fine. If you octane is too high just like 800AMSOIL4U said it'll actually run a little slower do to the slower burn rate of the fuel. If it's 95ish then you'd never see a difference but if you ran straight 100 on a stock motor then performance would suffer.

  5. #5
    vidbuster's Avatar
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    Thumbs up

    sweet, thanks guys.

  6. #6
    ADAMBOMB's Avatar
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    Hmm so anything higher is a waste of money? 93 and thats it. I only use 93 but was thinking of going higher.

  7. #7
    Quote Originally Posted by Speed200 View Post
    If you octane is too high just like 800AMSOIL4U said it'll actually run a little slower do to the slower burn rate of the fuel.

    Unless I'm forgetting something, I thought higher octane always burned faster/easier.

    Also....how high is too high an octane? I have also bene thinking of using octane boosters since all I get here is 91...unless I go to a station and get the 100, in which case, I was planning on mixing.

  8. #8

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    I'm certainly no hydrocarbons engineer, but it is my understanding that a higher percentage of octane carbon chains is only used to prevent predetonation of the fuel/air mixture upon compression of the piston before the spark fires. I think no matter the octane level, the spark is going to ignite the mixture to move the piston, you just don't want it to ignite because the gas is compressed. It is such a prevalent myth that high octane gas is "better" gas, when it is only better in a higher compression engine to prevent knocking.

  9. #9
    Speed200's Avatar
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    Quote Originally Posted by blkturbo! View Post
    Unless I'm forgetting something, I thought higher octane always burned faster/easier.

    Also....how high is too high an octane? I have also bene thinking of using octane boosters since all I get here is 91...unless I go to a station and get the 100, in which case, I was planning on mixing.
    The higher the octane the slower the fuel will burn. That's the reason higher octane is used in high compression and forced induction applications. The slower the fuel burns the less detonation proned. It's best to run the octane rating of the manufacture unless you have modded to a point that more octane is needed like more boost or compression. This is also the same reason some people run a step colder plug to slow down the ignition point.

    Hope this helps...

  10. #10
    Speed200's Avatar
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    Quote Originally Posted by ADAMBOMB View Post
    Hmm so anything higher is a waste of money? 93 and thats it. I only use 93 but was thinking of going higher.
    Unless your ski is modded with more boost then yes it most likely is a waste. It won't hurt you but can actually decrease performance.

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