Compression Ratio & Gas Question
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Compression Ratio & Gas Question

  1. #1
    Senior Member Cobra 02's Avatar
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    Default Compression Ratio & Gas Question

    At what compression ratio do you have to start using higher octane gas, lets say 10-1 approx hp 650 BBC.

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  3. #2
    Some guy obnoxious001's Avatar
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    Quote Originally Posted by Cobra 02 View Post
    At what compression ratio do you have to start using higher octane gas, lets say 10-1 approx hp 650 BBC.
    There are other variables to be considered, including camshaft, ignition timing and the type of usage. You didn't ask which particular octane, but you already know 87 octane will not work.

    As I previously told you, with your heavier boat, I would suggest 9.5-1 or under. What if someone sells you a bad load of gas?

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    Member hollbrow's Avatar
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    I asked the same question a few weeks ago- I have around 11:1 compression and I have been running a mix of 93 octane pump gas and 110 race gas at about 2:1 ratio.
    the engine seems to like it fine. I may could get by with a little less race gas, but I like to be safe.

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    Senior Member glastornjet73's Avatar
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    Quote Originally Posted by obnoxious001 View Post
    What if someone sells you a bad load of gas?
    VERY VERY good info especially if you are buying gas fro marinas with the alcohol content in the fuel now days it absorbs water VERY fast i seen a boat come in that got fuel lrom a marina at a local lake he has 3/4 tank of water and 1/4 tank of fuel

    also the carb has a lot to do with the type of fuel and compression you can run if there is a place neer you to get E-85 i would probly go with a carb set up for it people are making big numbers with the e-85 and higher ethanol fuel also what type of booster's are in your carb will help determin that of corse an annular boost carb is better at atomising the fuel therfore making better use of the fuel there are guys around here running ump sportsman cars (360 inch limit any non roller cam spec heads 2bbl and gasolene) that are running 13to1 on 93 using an aerosol carb just my .02

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    Senior Member CK7684's Avatar
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    Another factor is iron or alum heads?? Alum absorbs heat faster so you can get away with more compression...

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