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    Omc outdrive

    are all lower units 86 and up the same? I have an 89 5.0 ford 302 outdrive that I was thinking of using lower unit and changing gears in upper case with my 5.7 gears. My case is shot from electrolysis. Thoughts?
    1987 bayliner 2550 5.7 omc cobra i/o

    #2
    Yes, all V6 and V8 lowers (large bullet) are the same, as you stated the ratio difference is determined by the upper gear set.
    " WET EVER "
    1989 2459 TROPHY OFFSHORE 5.8L COBRA / SX
    mmsi 338108404
    mmsi 338124956
    "I started with nothing and still have most of it left"

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      #3
      How do I know if its a large?
      1987 bayliner 2550 5.7 omc cobra i/o

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        #4
        You have the 5.7 drive already ? if yes the drives are the the same interchangeable ... gears will be slighty different you can make it work with a prop tweak, in other words different prop say you have now a 19p you may have to go lower 2 degrees or more, some shops allow you to test props as long as you buy one from them the key is staying within recommended rpm at wot do not exceed capiche !
        Be good, be happy, for tomorrow is promised to no man !

        1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

        '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

        Manalapan N.J

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          #5
          FYI:
          ...... The engine HP/Torque (with some influence of the hull size/weight) determines the final gear reduction.
          ...... It is nearly impossible to prop ourselves out of an incorrect reduction.
          ...... Prop pitch is measured in inches, not degrees.
          Rick E. Gresham, Oregon
          2850 Bounty Sedan Flybridge model
          Twin 280 HP 5.7's w/ Closed Cooling
          Volvo Penta DuoProp Drives
          Kohler 4 CZ Gen Set

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            #6
            If my research is correct the 5.0 Ford is 21:18 and the 5.7 is 21:15.
            1987 bayliner 2550 5.7 omc cobra i/o

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              #7
              With the hull you have ...... use the correct ratio upper and if everything else is in good order the prop that will work best is a 15-1/2 x 15

              " WET EVER "
              1989 2459 TROPHY OFFSHORE 5.8L COBRA / SX
              mmsi 338108404
              mmsi 338124956
              "I started with nothing and still have most of it left"

              Comment


                #8
                I have the same prop (15.5x15) on my '88 4.3-4bbl Cobra for a 20' boat, the performance with it is excellent.
                88 Four Winns 200 Horizon 4.3 OMC
                98 Jeep Grand Cherokee 4.0/Selectrac
                07 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

                Long Island Sound Region

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                  #9
                  Originally posted by 6549vincent View Post
                  If my research is correct the 5.0 Ford is 21:18 and the 5.7 is 21:15.
                  those numbers convert to overall ratios of approx. 1.50:1 and 1.41:1, respectively.
                  But as noted for the large case lower units, all of them have the 14:26 gearing, the only different lower unit was on the early 2.3 and 3.0s (small case) these were 13:6 and the 460 Ford, (extra large case) this was 17:30

                  for the uppers its:
                  21:17 for the 5.0, 21:16 for the 5.7, as noted the lowers are the same.
                  88 Four Winns 200 Horizon 4.3 OMC
                  98 Jeep Grand Cherokee 4.0/Selectrac
                  07 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

                  Long Island Sound Region

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                    #10
                    21-16 gear set is the correct ratio for 5.7L at less than 5000 ft operating elevation.
                    " WET EVER "
                    1989 2459 TROPHY OFFSHORE 5.8L COBRA / SX
                    mmsi 338108404
                    mmsi 338124956
                    "I started with nothing and still have most of it left"

                    Comment


                      #11
                      How do i measure lower unit to see if this one i bought will work? According to prop number its for a 4 3/4 case. It has minor up and down movement at prop and normal fore and aft movement
                      1987 bayliner 2550 5.7 omc cobra i/o

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                        #12
                        Looks like the one I pulled is a 1.6 ratio as every 8 turns of driveshaft there's 5 prop revolutions
                        1987 bayliner 2550 5.7 omc cobra i/o

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