compression ratio versus octane requirements




















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  1. #1
    Join Date
    Dec 2010
    Posts
    29

    Default compression ratio versus octane requirements

    How high a compression ratio can you run and still run "pump gas" ie 93 octane?

  2. #2
    Join Date
    May 2007
    Location
    Glasgow, Kentucky
    Posts
    4,852

    Default

    It depends on the chambers, pistons and if there are any points that would develop hot spots. We had a motor in the early 90's that was 13:1 and it ran on pump 93 octane. The pistons and chambers were polished VERY VERY smooth and turbulance dimples were added to keep the fuel in suspension. The engine was specifically build by our engine builder to prove how dumb the fuel rule was at a specific track. The car was dominant in the class until they put in a 9:1 rule.

  3. #3
    Join Date
    Dec 2008
    Posts
    1,177

    Default

    like ego said,..depends on the combustion chamber an all,...i had a 340x motor,40 over 0 deck,..angle milled x heads,bout 588 lift cam,...holly 750,..ran 87 octane on the street an 93 on the strip for 11 years no problems,....but ive seen stock 350s spark knock an pre-detonated on 93....timing effects it all to,to some degree

  4. #4
    Join Date
    Oct 2008
    Location
    Michigan
    Posts
    79

    Default

    Static compression ratio does not play near as much of a role as dynamic compression. The intake valve closing point plays a huge role in this. A motor could be built with a very high static C.R. and run on pump gas, if the intake valve closed extremely late. I am not saying this is the best approach, but it is necessary to consider while calculating fuel needs.

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