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Repowering-Upgrading Twins

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  • Repowering-Upgrading Twins

    I am going to be buying 2 new long-blocks this week finally. Still trying to decide to upgrade. I have an 2001 Four Winns 298 Vista with twin Volvo Penta 5.7 GSI PEFS motors and 1.95 DP-SM duoprop drives. The motors are 280 HP TBI with MEFI 3 ECU. Just had injectors sent out to Witchhunter Peformance (cleaned/tested) and rebuilt throttlebody and fuel pumps. I plan on keeping OEM intake and TBI and having MEFI Bob remap ECU for 1 of the following long-blocks.

    VP 5.7 GXI 320 HP
    https://www.michiganmotorz.com/350ci...5-p-10888.html

    GM Marine 6.2 Stroker 340 HP
    https://www.michiganmotorz.com/377ci...ent-p-545.html

    GM HT383 323 HP
    https://www.chevrolet.com/performanc...l-block-ht-383

    I also plan on running Hardin Marines Seaward series exhaust and adding Freshwater cooling. What do you think?

  • #2
    I wouldn't mess with the Chevy street motor

    If you have a dollars to go 6.2 then I would go that route, but I would think about a 6.2 reman (actual 383 bored .030) and save 1200, the new base is a 377 (virgin bore)

    https://www.michiganmotorz.com/vorte...ent-p-945.html
    94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
    95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
    07 Seadoo GTX
    Merc Adults Only VP Adults Only
    G-Dad always said "First Liar doesn't stand a chance"

    Comment


    • #3
      Ayuh,..... Option #2 would be My choice,......

      Comes with a forged steel crankshaft; heavy duty rods; and forged aluminum pistons,
      Hmmmm,.... It would be interestin' to see the profile of the piston crowns,......

      GM's traditional full dish, or bein' forged, maybe a D-dish,..??.......

      Comment


      • #4
        Originally posted by AllDodge View Post
        I wouldn't mess with the Chevy street motor

        If you have a dollars to go 6.2 then I would go that route, but I would think about a 6.2 reman (actual 383 bored .030) and save 1200, the new base is a 377 (virgin bore)

        https://www.michiganmotorz.com/vorte...ent-p-945.html
        I didn't think of going reman but now I will look into it. I would assume they put new pistons and rings in. I will have to call

        Comment


        • #5
          Yes, fresh bore, pistons, rings etc

          You know, if you were in fresh water, you could rebuild your old block and build a 383
          94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
          95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
          07 Seadoo GTX
          Merc Adults Only VP Adults Only
          G-Dad always said "First Liar doesn't stand a chance"

          Comment


          • #6
            You can build new 350 or 377 yourself for about $4k. About same cost as reconditioning your current block and heads

            New gm block is $750
            New vortec heads $650
            New scat rotating assembly $900
            new comp cam k-kit $900
            new felpro gaskets $150
            Oil pump and dizzy drive $70
            brass core plugs $11
            New stamped steel oil pan $120
            Hardware $200

            Modifying the heads for screw in rocker studs and for cam lifts higher than .420, about $200

            Check with your local engine builder on rebuilding yours
            Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

            1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

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

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

            Comment


            • #7
              Current motors are 18 years old, I am the 4th owner. Boat was originally sold in Florida so had salt. That is why I want new/different motor. I didn't price machining/assembly cost locally, but based on other posts i think it would cost more than buying a long block. Now I am running into time issues so just want to get this done.

              Comment


              • #8
                Originally posted by Lubak572 View Post
                Current motors are 18 years old, I am the 4th owner. Boat was originally sold in Florida so had salt. That is why I want new/different motor. I didn't price machining/assembly cost locally, but based on other posts i think it would cost more than buying a long block. Now I am running into time issues so just want to get this done.
                just talk to your local machinist and get pricing. some times they have really good deals.
                Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

                1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

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

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

                Comment


                • #9
                  So jealous that you guys have such options available to you. Amazing.

                  Comment


                  • #10
                    I purchased a new Michigan Motorz engine last fall, VP 320 HP. While the new motor is not yet installed in the boat, I was pleased with the purchase and shipping process. They seem to know what they are doing.
                    Summer Fling-II
                    2008 Chaparral Sunesta 264
                    Summer Fling
                    2003 Chaparral Sunesta 243

                    Comment


                    • #11
                      Originally posted by QBhoy View Post
                      So jealous that you guys have such options available to you. Amazing.
                      The ubiquitous Chevrolet small block used to power millions of cars here. Still being built for marine and industrial use.
                      It started in 1955, 265 cu in, then went to over the years:
                      283
                      305
                      307
                      327
                      350
                      400
                      also destroked to 302 cu in for Trans Am racing sold that way in the original Z//28 Camaro

                      What you can have when the government doesn't over-regulate and tell you what you have the right to drive. A good thing for all Americans to remember.


                      1988 Four Winns 200 Horizon
                      4.3 OMC Cobra

                      98 Jeep Grand Cherokee 4.0 Selectrac
                      07 Jeep Grand Cherokee Limited 5.7 Quadradrive II

                      "While air doesn't freeze....rust never sleeps"

                      Comment


                      • #12
                        Agree with that....fuel cost and the road tax such engines would result in....just don't make them viable here. The preference for most is smaller displacement and more advanced wizardry to make up the horsepower. Jeez, my bmw diesel car has about as much HP as my V8 MPI with a cam and exhausts....and it's only a 3.0....prefer the V8 any day though.

                        Comment


                        • #13
                          Got my Exhaust....new 6.2's are on the way!

                          Comment


                          • #14
                            The exhaust have a low rise, you sure they are high enough to keep reversion down?
                            94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                            95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                            07 Seadoo GTX
                            Merc Adults Only VP Adults Only
                            G-Dad always said "First Liar doesn't stand a chance"

                            Comment


                            • #15
                              Sign up today
                              Yes I have to raise it a hair about a 1/2 inch. We had them side by side at the shop. I will make it work.

                              Comment

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