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Possible new engine question

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  • Possible new engine question

    So, as many will know already, I have a pretty brisk boat with a 5.0 Mpi Merc.
    The engine is a great thing when not throwing sensor issues at me and is in great condition....
    Only thing is that I have a never ending urge to get a little more speed out of her and would love to break the 70mph barrier. I am aware that this is a huge barrier to break in real terms and hp to weight proportions.
    On a good day, she will get well into the 60's and has even seen 66.7 gps with a 21" prop...problem was that the 21" was pretty useless in all other areas.
    So, the problem is....
    I was recently walking through the workshop door of the local Merc dealer....when I was presented with a lovely big 350mpi still in the crate...he then told me it would slot straight into my boat no problem and align with the Corsa Marine exhaust perfectly, as the 5.0 does. Man, I'm so tempted but as far as I am les to believe, my 5.0 has a cam from new so might the difference be so small I may not notice the difference and just find myself £10000 out of pocket ? Will the 350 really make all that much of a difference ? It may turn the 21" better I suppose ?
    Further to this...it begs the question...if I go this far...do I go for the 6.2 mpi ? Would this slot straight in and is the extra 20hp (I think) worth the extra fuel she will sook over the 350 ?
    Thoughts please ? Tell me I'm being daft...please !

  • #2
    Tell me I'm being daft...please !
    Ayuh,.... Yer bein' Daft,.....

    Trade that slug of a boat, for the boat ya Really want,.....

    Drop $20,Grand into a hull, 'n it's still worth exactly what it's worth Today,....

    Comment


    • #3
      Haha...thanks Bondo.
      Normally I'd agree completely, but she is a special wee thing. Only one in the country and couldn't think about getting rid of her just yet. One for the garage in her later years.

      Comment


      • #4
        Also thinking I'd surely get at least half the financial outlay back when I sell the 5.0 mpi. Pretty sought after over here, from what I gather.

        Comment


        • #5
          Your going down fast and no life saver is going to fix it. Your hull is not long enough to gain much more speed. The 5.0 MPI is not much better then a V6 MPI. There is a bit more to pull out of the 5.0 but not that much so not worth it IMO. Going to a 6.2 is the way to go but then your getting close to or above 70 mph ((112 kph) you need to invest in hydraulic steering. Even with hydraulic steering you can get into chine walking without enough hull in the water
          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
            Have you looked into getting a carbed 383 built?
            I'd think it would be a lot less than that 5.0 mpi from mercury even in your neck of the woods.
            1980 Sylvan Aluminum 18' Sportster I/O - Mercruiser 140, Honda 7.5 Kicker, Bennett M120 Tabs
            1974 Glastron V-179, Mercruiser 140
            1984 16.5ft. Alumarine Sealark side console with 82 Merc 50
            Manitoba, Canada

            Comment


            • #7
              Thanks both...I already have the 5.0 mpi fitted. It was more the 350mpi or 6.2 mpi I was looking at.
              I have heard of a 383....is that the stroker engine it's called ? Is there not an mpi version of that...6.3l or something. Would like to stick with the mpi.

              Comment


              • #8
                It has hydraulic steering AD.

                Comment


                • #9
                  AD...surely the hull length is negligible in this case ? She only really has the drive and around 6inches of the hull in the water when running quick.

                  Comment


                  • #10
                    a new gen 1 SBC 6.2 liter from Mercruiser is 377cubic inches (3.75" stroked 350 with stock bores). a 383 is a 0.030" over bore with the 3.75" stroke essentially same motor (one with virgin bore, one with a re-machined bore).

                    the 5.0 and 5.7 (and all the bore/stroke variations) share the same outer dimensions

                    while the 5.7 will drop in place, you state it will cost you 10k pounds ($13k USD). FYI - it would only cost you $4.8k USD to buy a 383 long block and ship it over https://www.summitracing.com/parts/nal-19355720 that is 3700 pounds plus shipping / customs. then you only need your ECM re-flashed.

                    however why stop there.

                    you could have a tall-deck 432 cubic inch, 600hp monster built. however you would need a custom drive similar to the RLC custom drive http://www.rlcperformance.com/images...pledigits.html

                    or you could enjoy your boat and put the extra cash into the fuel tank and cooler
                    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

                    Comment


                    • #11
                      Originally posted by QBhoy View Post
                      AD...surely the hull length is negligible in this case ? She only really has the drive and around 6inches of the hull in the water when running quick.
                      That's the thing when your at that stage it takes very little to get in trouble. This is why boats go to hydraulic steering, this get rid of all slop/play in the steering. Could look up chine walking on you tube
                      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


                      • #12
                        Oh jeez Scott. You have me thinking now. Thanks for the link. Superb.
                        AD...yeah, I'm well aware of chine walking. I used to have a ring 18 racing hull that was famous for it. Haha.
                        The boat has hydraulic steering already.

                        Comment


                        • #13
                          Wondering why this was redirected ? It was clearly a Mercruiser question for the Mercruiser experts.
                          Mmm.

                          Comment


                          • #14
                            Pretty sure, Its because its not a repair topic/question, so its in the non-repair area
                            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


                            • #15
                              Sign up today
                              If the engine you finally decide on has a belt driven raw water pump be sure to have a through hull water supply for the engine.
                              1980 Donzi 18'. 2+3 6.2 MPI Alpha 1

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