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Thread: 49 ci compression

  1. #1
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    Default 49 ci compression

    without reinventing the wheel I wan to build a 49 ci omc for an aquarius tunnel. This is strictly a play boat. I am cutting finger PORTS in the motor at this time. was planning on duplicating the sst60 tuner. Is this to short for the 49" motor. Exhaust ports are widened. i chose not to raise them. This is a 1975 stinger block. Left the bridges alone. What cc should be my target on the head for 150 psi. I have always felt thats about the limit on pump gas. Gonna run stock carbs and ccms reeds. Thanks for any input.

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    Good to hear of a thundercat build! Fast Fred or Bill Gore would surely know, among other people. Maybe they'll see this. Good luck with the build.

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    Team Member DeanFHobart's Avatar
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    Call Dave Losvar at Sea Way Marine….425-412-5914…. He would know or at least access to the Factory manual. Sea Way specializes in the older motors…. All of them. Good luck.
    Dean Hobart

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    You can mill lots off of the cylider head ( like .080" + )& not get much compression increase.Motor has flat top pistons & flat head with small dome in head. Milling head .080 thinner only lowered cc's by 1cc..(Same applies to the 49.7 triple l did See below) ( did it long ago) for my 1989 d-mod motor( CBF, Canada) rules. Mill .010-.015" from block & crush new head gasket in hydrolic press.Need two machined pieces of thick steel to put gasket in middle of , then press. My motor showed 170psi after this.Thats boaderline for pump gas. l also kept various thickness head gaskets to vary compression.
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    Sorry, thats what i did to my twin Evenrude 44.9 motor. l also build an economy 49.7 triple for FEH class. .Milled .015" from block but did not crush gasket.( no thick plates big enough).Some makes of head gaskets are thinner than others. I usused the thinner one of three l ordered. Got 150psi.Motor worked great Hope this is some help..DD

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