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Interchanging lower-units

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  • Interchanging lower-units

    I was reading some of the earlier post on interchanging lower-units but they were for different years/application.

    I have a 1990 model year(89 build) Force 90 hp motor with 2 spare (parts) Lower Units, they're all with a 2 piece drive-shaft
    but the two "spares" are dual exhaust and the one on the motor is single port exhaust.

    I read the Gear-ratio is the same on the lower-units and as far I was able to measure the mounting hole's location it seems to be the same;

    my question is will a dual exhaust port lower unit affect the back pressure in the motor if it had a single exhaust-port?
    working on 1990 force 90 horsepower Engine serial. 17523 Engine model. 906X90B

  • #2
    Probably help make a fraction more HP, as less Back Pressure is better
    Last edited by jimmbo; February 10th, 2019, 10:19 PM.

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    • #3
      Shouldn't really make much difference.


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      • #4
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        Hmm, interesting
        thanks guys
        working on 1990 force 90 horsepower Engine serial. 17523 Engine model. 906X90B

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