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2556 - Alpha Drive Owners, please confirm RPM VS. Speed

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    2556 - Alpha Drive Owners, please confirm RPM VS. Speed

    Hello BOC Members,

    I am having some performance issues with my 1991 - 2556 Bayliner.

    Over the past year, I have installed a new Mercruiser 357 MAG Engine along with a new Alpha Drive GEN 1 (waiting on confirmation of drive ratio).

    Currently, I am only reaching speeds of 10 - 11 MPH @ 2800 - 3200 RPM. When doing an open throttle test, I am only reaching a max RPM of 3800 - 4200 RPM and reaching a maximum speed of 13 MPH. (SOG)

    My prop size is 15 1/2" 15P (is this prop size the same as what other 2556 owners are using with an alpha drive?)

    I have electric trim tabs and even without those, the boat has no issued getting up on plain... lots of torque.

    I have installed a hydrofoil as of yesterday to be tested this weekend for any improvements. ...

    Any comments back confirming you own speeds and specs would be greatly appreciated! My gut is telling me perhaps the shop that ordered me the drive either ordered the wrong ration drive or received the incorrect ratio drive..... hmmmm and so goes on the mystery....
    Last edited by Jim_Gandee; 07-08-2018, 09:42 AM.
    BOAT: 1991 - Bayliner 2556 Ciera Flybridge
    ENGINE: 357 Alpha 4V (275HP)
    OUTDRIVE: Alpha Gen 1
    RATIO: (to be updated)
    PROP: 15 1/2" X 15P
    NAME: "Knotty Oar"

    Marine Search and Rescue Crew - http://rcmsar.com/rescue-stations/southern-region/north-vancouver/

    #2
    Your 91 MY boat should've had a GEN2 to start with...

    Positive they ordered a GEN 1? sounds like your gear ratio is wrong also
    Joon, Kathy, Jaden & Tristan
    Uniflite 42 AC, DD 671N
    93 3058 sold
    92 2855 (day boat)
    91 Fourwinns 205 (lake boat)
    Longbranch WA
    Life is Good

    Comment


      #3
      Joon, can you confirm what the final drive ratio should be on a 2556 with SBC engine and Alpha? I don't have a clue as a run the Bravo. I'd thinks he should be cruising easily at 20-22 mph.

      Landin, is there a maximum recomended RPM on the flame arrestor cover? I'd think at least 4600 for WOT on that 357 MAG
      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


        #4
        Hi Dave, Merc. indicated 4400-4800 RPM
        BOAT: 1991 - Bayliner 2556 Ciera Flybridge
        ENGINE: 357 Alpha 4V (275HP)
        OUTDRIVE: Alpha Gen 1
        RATIO: (to be updated)
        PROP: 15 1/2" X 15P
        NAME: "Knotty Oar"

        Marine Search and Rescue Crew - http://rcmsar.com/rescue-stations/southern-region/north-vancouver/

        Comment


          #5
          I'll double check the GEN 1 VS. GEN 2 with the shop... Thx!
          BOAT: 1991 - Bayliner 2556 Ciera Flybridge
          ENGINE: 357 Alpha 4V (275HP)
          OUTDRIVE: Alpha Gen 1
          RATIO: (to be updated)
          PROP: 15 1/2" X 15P
          NAME: "Knotty Oar"

          Marine Search and Rescue Crew - http://rcmsar.com/rescue-stations/southern-region/north-vancouver/

          Comment


            #6
            recommended WOT RPM on a 357 4V Alpha is 4400-4800.

            mated Alpha final ratio should be 1.47:1 or HIGH ALTITUDE 1.81:1
            Joon, Kathy, Jaden & Tristan
            Uniflite 42 AC, DD 671N
            93 3058 sold
            92 2855 (day boat)
            91 Fourwinns 205 (lake boat)
            Longbranch WA
            Life is Good

            Comment


              #7
              Thank-you Joon!
              BOAT: 1991 - Bayliner 2556 Ciera Flybridge
              ENGINE: 357 Alpha 4V (275HP)
              OUTDRIVE: Alpha Gen 1
              RATIO: (to be updated)
              PROP: 15 1/2" X 15P
              NAME: "Knotty Oar"

              Marine Search and Rescue Crew - http://rcmsar.com/rescue-stations/southern-region/north-vancouver/

              Comment


                #8
                "Ruffryder" post=823371 wrote:
                recommended WOT RPM on a 357 4V Alpha is 4400-4800.

                mated Alpha final ratio should be 1.47:1 or HIGH ALTITUDE 1.81:1
                Landin, Sounds like you go for some extended trips and could be heavily loaded with fuel, water, gear, & crew. If you determine the drive ratio is correct it's gotta be to much prop. reduce the prop pitch to achieve your maximum recommended RPM range of 4800 (IMO your mechanic should have tested this)

                Also, have you done any testing with the boat lightly loaded? Say half tank of fuel, no water, and no gear?
                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


                  #9
                  Hi Dave,

                  I have noticed maybe (max) 500 extra RPM with min. Fuel/water and gear... giving me a maximum throttle of 3800 RPM. And still never exceeding 14mph.

                  I just got back from testing the newly installed hydrofoil... no improvement.

                  I came up with the following results -

                  At 3000 Rpm. Boat speed was around 12 mph... Max throttle today was 3400 RPM... I had some gear on board (not much) full fuel tank and no water.

                  Joon, may I ask what prop specs you're running?

                  Dave, I understand prop sizing is more of an art than a science... but; Is changing my prop size , say from a 15pitch to a 13pitch - Could it really improve my overall speed 10 - 15 mph...this seems like a huge jump?

                  Nother big question is how do I test a 13 pitch prop without having to buy one... I heard mercury use to lend out props for prop sizing but don't think that sort of stuff happened anymore... :/

                  Cheers┬░┬░┬░
                  BOAT: 1991 - Bayliner 2556 Ciera Flybridge
                  ENGINE: 357 Alpha 4V (275HP)
                  OUTDRIVE: Alpha Gen 1
                  RATIO: (to be updated)
                  PROP: 15 1/2" X 15P
                  NAME: "Knotty Oar"

                  Marine Search and Rescue Crew - http://rcmsar.com/rescue-stations/southern-region/north-vancouver/

                  Comment


                    #10
                    Landin, take a look through the 2556 owners thread. Mojo25 !has a similar set up (5.7 Alpha gen 1) maybe send him a pm asking what prop he's running & drive ratio. There are also many 2556 members running OMC drives, maybe it's a simalar prop as far as diameter goes and such.
                    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


                      #11
                      My '92 2556 with carbureted 350 was a dog. Motor had 200hrs after rebuild. Receipts that came with it showed the carb had be rebuilt recently.

                      I was quite disappointed that it would not go more than 13-14 mph. Wouldn't rev right up under load.

                      I replaced the carb with a brand new one. And bingo, 24 MPH (18-21 mph fully loaded with water fuel kids and overnight gear).

                      The prop is a 15x15. I wouldn't change it.

                      Comment


                        #12
                        "Vanisle boater" post=824121 wrote:
                        My '92 2556 with carbureted 350 was a dog. Motor had 200hrs after rebuild. Receipts that came with it showed the carb had be rebuilt recently.

                        I was quite disappointed that it would not go more than 13-14 mph. Wouldn't rev right up under load.

                        I replaced the carb with a brand new one. And bingo, 24 MPH (18-21 mph fully loaded with water fuel kids and overnight gear).

                        The prop is a 15x15. I wouldn't change it.
                        This is good info for the OP, not sure if his new engine came equiped with a new carburator or not but it's possible a fuel delivery issue is causing the poor performance.
                        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


                          #13
                          Yup... brand new carb.

                          I'm having a mechanic sea trial it this upcoming week.....some interesting info... boat mechanics boss said the matched ratio drive for my engine is a 1:67 and currently my drive is a 1:47...

                          ....a bit of history on the boat - approx.14 months ago the engine and engine components were replaced new.... then about 1 week later the drive seized....so the shop ordered and installed a new drive ( 1:47 ratio, alpha gen 1).... now I am assuming the shop whom ordered the new drive (same shop purchased and installed the engine) should have spec'd the correct drive for the engine they installed, right!?????
                          BOAT: 1991 - Bayliner 2556 Ciera Flybridge
                          ENGINE: 357 Alpha 4V (275HP)
                          OUTDRIVE: Alpha Gen 1
                          RATIO: (to be updated)
                          PROP: 15 1/2" X 15P
                          NAME: "Knotty Oar"

                          Marine Search and Rescue Crew - http://rcmsar.com/rescue-stations/southern-region/north-vancouver/

                          Comment


                            #14
                            What speeds were you getting before the original new drive seized? Or did you purchase the boat after?

                            Yes shop should have replaced it with the same ratio unless they were instructed to do different :S . So you thinking it's a ratio issue then? I hope you get it figured out, I made a run today at 3700 RPM @ 28 MPH
                            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


                              #15
                              your boat mechanic's boss has been smoking tough... 1.67 gear ratio doesn't even exist.

                              correct gear ratio 1.65 GEN 1 OR 1.62 GEN 2 IS NOT for your engine, this gear ratio is for lower HP 5.0.

                              Once again you stated that you have a GEN 1 1.47 on her... 1.47 not even available on GEN 1.
                              Joon, Kathy, Jaden & Tristan
                              Uniflite 42 AC, DD 671N
                              93 3058 sold
                              92 2855 (day boat)
                              91 Fourwinns 205 (lake boat)
                              Longbranch WA
                              Life is Good

                              Comment

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