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Thread: compression

  1. #1
    RHeller1's Avatar
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    compression

    What is the highest compression with 87 octane,89 octane and 91 octane?


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    Moderator OsideBill's Avatar
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    Personaly I never go over 145-150 on 91 octane.

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    Moderator beerdart's Avatar
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    100 MILES OF HEAVEN AND I AM SMACK IN THE MIDDLE KEYZBUM's Avatar
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    Last edited by KEYZBUM; 09-07-2008 at 09:36 AM. Reason: i type TOO SLOW GRRRRRR

  5. #5
    Moderator OsideBill's Avatar
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    According to this chart I should not run over 120 compression on 91 oct. I take exception to this.

  6. #6
    TRIPLE PIPES ARE 2-STROKE TURBOS allcool's Avatar
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    Quote Originally Posted by beerdart View Post
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    Nice chart beerdart...although I don't think it takes all the variables into considerations.

    How about squish band variables... the reverse squish angle that comes on a yamaha head, makes some slightly higher comp ratios prone to detonation imo.

    You can have the same head volume and comp ratio with very different squish band sizes and squish clearances.

    Squish band size, diameter and clearance make a huge difference in deto resistance and power delivery.

    My point being on a 2-stroke, comp ratio is only part of octane selection...imho.

    allcool

  7. #7
    Moderator beerdart's Avatar
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    Quote Originally Posted by OsideBill View Post
    According to this chart I should not run over 120 compression on 91 oct. I take exception to this.
    Bill did you do the math?

  8. #8
    Moderator beerdart's Avatar
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    Quote Originally Posted by allcool View Post
    Nice chart beerdart...although I don't think it takes all the variables into considerations.

    How about squish band variables... the reverse squish angle that comes on a yamaha head, makes some slightly higher comp ratios prone to detonation imo.

    You can have the same head volume and comp ratio with very different squish band sizes and squish clearances.

    Squish band size, diameter and clearance make a huge difference in deto resistance and power delivery.

    My point being on a 2-stroke, comp ratio is only part of octane selection...imho.

    allcool

    Very true..

  9. #9
    Moderator OsideBill's Avatar
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    Quote Originally Posted by beerdart View Post
    Bill did you do the math?
    Nope too lazy I use this spreadsheet, I have an uncorrected compression ratio of 11.3 but that was just guessing at the CC's I need to dig out my paperwork from lowell for actual.
    Attached Files Attached Files

  10. #10
    Moderator beerdart's Avatar
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    I just did the math for my 1200 and I get 11.56. So at 150psi compression I should run min 88 octane and max 92.

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