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Thread: Johnson 40 hp mods

  1. #11
    Team Member LittleCharger's Avatar
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    Quote Originally Posted by Kevodaniel View Post
    I'm runnin 150 psi compression with a 40hp head and I'm putting a 50 hp head on it if I have it milled to 45 sst spec will I be running too much compression
    Did you deck your block, if so to what spec.

    Compression won't be a problem, you may have to upgrade to a higher octane fuel

  2. #12
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    I did not deck the block I was told with my motor having 150psi if I had the head milled it would have too much compression I can not find the spec on the 50 hp head to compare 45 sst head too I don't want to run over 93 pump gas

  3. #13
    Team Member LittleCharger's Avatar
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    Quote Originally Posted by Kevodaniel View Post
    I did not deck the block I was told with my motor having 150psi if I had the head milled it would have too much compression I can not find the spec on the 50 hp head to compare 45 sst head too I don't want to run over 93 pump gas
    I guess one needs to define "too much compression"...these will run with 200 psi so I assume your definition is of "too much compression" is based on the fuel you are willing to run.

    I'm surprised the compression with the 40 head is that high if your block is not decked.

    If you have the 50 head measure the pocket depth versus the sst45 spec to get a rough idea of the difference.

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