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Thread: outboard gear ratio

  1. #1
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    Talking outboard gear ratio

    I've seen speedmaster cases with a 16/21 gear set. Does this mean that the engine spins 16 times to the props 21 times or the other way? What RPM do the engines run at that have these cases.
    I'm in the process of setting up the gear (sprocket) box for prop speed. I know my engine speed.
    Oh yea, I'm the guy thats building the surface drive, motorcycle powered hydro.
    I can't do anything NORMAL.
    Last edited by stupidbaker57; 10-14-2011 at 05:26 AM. Reason: spelling

  2. #2
    Team Member david bryan's Avatar
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    Default rpm

    [QUOTE=stupidbaker57;112022]I've seen speedmaster cases with a 16/21 gear set. Does this mean that the engine spins 16 times to the props 21 times or the other way? What RPM do the engines run at that have these cases.
    I'm in the process of setting up the gear (sprocket) box for prop speed. I know my engine speed.
    Oh yea, I'm the guy thats building the surface drive, motorcycle powered hydro.
    I can't do anything NORMAL.[/Qeng engine 21 prop 16
    David Bryan

  3. #3
    David_L6
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    That's the number of teeth on each gear. 16 teeth on the drive gear, 21 teeth on the driven gear. It's a reduction ratio - not overdrive.

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    Team Member ProHydroRacer's Avatar
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    Quote Originally Posted by stupidbaker57 View Post
    I've seen speedmaster cases with a 16/21 gear set. Does this mean that the engine spins 16 times to the props 21 times or the other way? What RPM do the engines run at that have these cases.
    I'm in the process of setting up the gear (sprocket) box for prop speed. I know my engine speed.
    Oh yea, I'm the guy thats building the surface drive, motorcycle powered hydro.
    I can't do anything NORMAL.
    16/21= .762 x RPM =Prop RPM

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