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Mercury tower of power gear ratio

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  • Mercury tower of power gear ratio

    I have an 87 115 L6. I was looking through the specifications the other day and notices it has a 2:1 gear ratio in the lower unit. I also noticed that some of the other years came with at 1.78:1 ratio. Does the ratio increase the top in or bottom end? I'm not familiar with the relationship of the two gears and the effect on prop RPM. I was a little surprised there weren't more ratios offered.
    Miss Morgan,1969 Sleekcraft "Boats by Nescher" Newport. Power by Mercury 115 L6, tower of power.
    https://forums.iboats.com/showthread.php?t=364284

    Current project,https://forums.iboats.com/forum/boat...project-fuggly

    "Nothing is done so poorly that the government can’t do it worse!"

    “It’s easy being a humorist when you’ve got the whole government working for you.”—Will Rogers

  • #2
    Re: Mercury tower of power gear ratio

    The ratio's are just like in a truck, the lower numerically (1.78) will have a higher top speed and the higher (1:2) will have a better hole shot, all this is assuming same boat and same prop.
    1997 Crownline 202 BR
    5.7L Merc. w/ Alpha 1 Gen. II


    Sold 1974 15'6" Mark Twain with a '79 115 HP Merc' Tower of Power.

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    • #3
      Re: Mercury tower of power gear ratio

      Tower, You forgot to add that the higher gear ratio will give higher top speed, if the motor has the power for it.

      The real reason for the different gear ratios is to allow the motor to reach the max recommended RPM with a standard prop on a standard boat. More powerful motors has the higher gear ratios ie 1.75::1 versus 2::1.

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      • #4
        Re: Mercury tower of power gear ratio

        that is what I thought, so a 1.78 will have a higher top end, assuming the motor has the power to push the boat with that gear ratio.
        Miss Morgan,1969 Sleekcraft "Boats by Nescher" Newport. Power by Mercury 115 L6, tower of power.
        https://forums.iboats.com/showthread.php?t=364284

        Current project,https://forums.iboats.com/forum/boat...project-fuggly

        "Nothing is done so poorly that the government can’t do it worse!"

        “It’s easy being a humorist when you’ve got the whole government working for you.”—Will Rogers

        Comment


        • #5
          Re: Mercury tower of power gear ratio

          Originally posted by archbuilder View Post
          that is what I thought, so a 1.78 will have a higher top end, assuming the motor has the power to push the boat with that gear ratio.
          I'm certain that the 1.78 gear ratio is standard. The 2.0 gear ratio is considered for "high altitude" use.
          Dave

          2000 Larson SEi186 - Merc 150hp XR4

          1987 Seaswirl Spyder 17' - OMC Cobra 5.7L 260hp

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          • #6
            Re: Mercury tower of power gear ratio

            Dave, The inline sixes normally have a 2::1 gear ratio, as do the 135-150 HP V6 Mercs.

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            • #7
              Sign up today
              Re: Mercury tower of power gear ratio

              Thanks for the info. Will the 1.78:1 gear set up fit in a 2:1 housing?
              Miss Morgan,1969 Sleekcraft "Boats by Nescher" Newport. Power by Mercury 115 L6, tower of power.
              https://forums.iboats.com/showthread.php?t=364284

              Current project,https://forums.iboats.com/forum/boat...project-fuggly

              "Nothing is done so poorly that the government can’t do it worse!"

              “It’s easy being a humorist when you’ve got the whole government working for you.”—Will Rogers

              Comment

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