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4.3 to 5.7 mercruiser swap

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  • 4.3 to 5.7 mercruiser swap

    I have a 4.3 mercruiser/alpha 1 outdrive setup in a 94 JC 266 tritoon.

    Is a 5.7 going to mate up with the the alpha 1 outdrive, a plug and play more or less. I'd assume motor mounts would have to change....and I understand I'd have to be easy on the alpha 1 due to the increased horsepower.

  • #2
    Yes, both motors use the same drive
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
    07 SeaDoo GTX
    Raw Water Pump Maintenance
    Merc Adults Only

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    • #3
      outdrive strength is not the issue, as same outdrive is behind the 3.0, 4.3, 5.0, and 5.7. gear ratios are different between the 4.3 and 5.7. however with a 'toon, your motor pod may not be strong enough for the 5.7. would hate for you to mash the trottle only to hear a thud and watch your motor pot take off without the rest of the boat (dont laugh, plenty of threads about motor pods falling off pontoons)
      1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - http://forums.iboats.com/forum/owner...988-rogue-2420

      Past Boats
      1970 Wooster Hellion - Merc 9.8
      2002 SeaRay 190BR - 5.0 - A1G2 - "Cheasheads in Paradise"
      1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

      What’s behind you doesn’t matter.Enzo Ferrari

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      • #4
        I know the placard states it's rated for 250HP. I think the 5.7's are around that HP. How would one tell if the pot could hold a 5.7?

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        • #5
          I think it should be ok but I'm not seeing how its built. Just need to look and see if there would be an issue
          94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
          95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
          07 SeaDoo GTX
          Raw Water Pump Maintenance
          Merc Adults Only

          Comment


          • #6
            It's engine poD not poT. A project like this is not going to be a drop in and bolt up operation like it might be in a car. Of course the V8 is going to need more room than the V6, and it's going to be significantly heavier. This means the boat is going to sit lower in the water. Also, the boat may need to be reinforced. Both the engine pod itself, and it's attach points may need to be beefed up.

            I guess the bigger point is, my thoughts are that this project will require some expert input. May not be the best shade tree project.

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            • #7
              So I just picked up the boat tonight. I can't find the size or pitch of the prop stamped on it. Don't know how reliable the rpm gauge is.... But it turned 5800 to 6000 full throttle. I'm hoping it was wrong, but this prop looks too small also. Anyone have any ideas on its size? It currently has a 4.3 mercruiser 4 barrel new vortec heads. Shouldn't it be 4400 to 4800 range?

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              • #8
                Take the prop off, many have it stamped on the end
                94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                07 SeaDoo GTX
                Raw Water Pump Maintenance
                Merc Adults Only

                Comment


                • #9
                  I think auto correct is changing pod to pot.
                  Originally posted by ahicks View Post
                  It's engine poD not poT. A project like this is not going to be a drop in and bolt up operation like it might be in a car. Of course the V8 is going to need more room than the V6, and it's going to be significantly heavier. This means the boat is going to sit lower in the water. Also, the boat may need to be reinforced. Both the engine pod itself, and it's attach points may need to be beefed up.

                  I guess the bigger point is, my thoughts are that this project will require some expert input. May not be the best shade tree project.

                  Comment


                  • #10
                    I don't think that tach could be right. If so I am suprised that motor hasn't come apart yet

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                    • #11
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                      Ran it again today. I ran 23 mph at about 4400. Not even 3/4 throttle. Tach seems to be right up to there. But WOT jumps to 6K really quick, may not be quite 6K.... But I still think it's the turning too many rpms. Picking up a laser photo tachometer soon to check it at crank. Took prop off in my pictures in earlier posts... no stamps anywhere of diameter or pitch.

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