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Ciera 285 gear-ratio

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    Ciera 285 gear-ratio

    Hi. I have ciera 2850 with diesel motor (mercruiser 7,3L). Diesel motor is now dead and I have replace it with gasol motor (mercruiser 7,4L mpi 330hp).
    I have bravo tree (1=2) and 24” propeller.
    what is the right gear-ratio? And with what propeller?
    I have try 26”, 24”, 22,5” & 22” mercruiser propeller and 24” solas propeller. 26” was too big but all other work same (not good).
    So i have to change the gear-rotation (may be 1=2,2) ,but this model boat has made whit this motor. What is the orginal gear-ratio and propeller?
    Last edited by Vertti; 11-15-2017, 07:52 AM.

    #2
    I have no clue. But the diesel will turn lower rpms, so im guessing the gear ratio will be higher than normal. Might be able to get away with trying different props. Just do a wot test to see if you can pull it off without changing gear ratio.
    1993 formula pc 31 twin 454 bravo 2
    1989 2655 cierra 5.7 omc cobra
    2014 "searay" tandom trailer

    Anchor bay clinton river
    Michigan

    Comment


      #3
      If its a higher gear ratio, you want to go smaller prop diameter and pitch to get it in the ball park.

      Also that mpi 454 should be 330-350 hp

      also also, if you pull your drive (which should be off if repower) you can spin you drive shaft and count the roations of the prop to find your gear ratio. A good prop shop should be able to advise you from there. Fill out your sig with ypur boat info and location. Good prop shops are hard to find. I know of one in michigan, one.
      1993 formula pc 31 twin 454 bravo 2
      1989 2655 cierra 5.7 omc cobra
      2014 "searay" tandom trailer

      Anchor bay clinton river
      Michigan

      Comment


        #4
        Counting shaft rotation of the drive to figure out the final drive ratio:
        While in gear, You'll count the number revolutions the input shaft makes to one full revolution of the prop shaft.
        OP, you sure it's an Alpha?
        add your details....
        Dave
        Edmonds, WA
        "THE FIX"
        '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
        (.030 over-Vortec top end-part closed cooled)
        The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
        Misc. projects thread
        https://www.baylinerownersclub.org/f...56-gctid789773

        Comment


          #5
          Originally posted by builderdude View Post
          Counting shaft rotation of the drive to figure out the final drive ratio:
          While in gear, You'll count the number revolutions the input shaft makes to one full revolution of the prop shaft.
          OP, you sure it's an Alpha?
          add your details....
          no Alpha mated to a diesel, it’s a Bravo 3.

          1997 Maxum 2400 SCR 5.7LX Bravo II

          Mike

          Comment


            #6
            Kinda what I was thinking.
            Dave
            Edmonds, WA
            "THE FIX"
            '93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
            (.030 over-Vortec top end-part closed cooled)
            The rebuild of my 2556 https://www.baylinerownersclub.org/f...76?view=thread
            Misc. projects thread
            https://www.baylinerownersclub.org/f...56-gctid789773

            Comment

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