Announcement

Collapse
No announcement yet.

has anyone converted from 350 to 8.1/496 ,cost,difficulty parts needed?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    has anyone converted from 350 to 8.1/496 ,cost,difficulty parts needed?

    wondering if this is doable?

    #2
    Lots of factors. Here are a few.

    1. What boat and can it support the 8.1?
    2. Current drive and is it rated for the 8.1?
    3. If answer 2 is yes then the question is the gear ratio correct for the 8.1?
    4. Are you getting the 8.1 as a package with the transom mount?

    1997 Maxum 2400 SCR 5.7LX Bravo II

    Mike

    Comment


      #3
      Bigger question is WHY? the 350 is such a reliable and easy motor to run and will give you more power than you'll ever need if done right. For the same money you can convert a carbureted 350 to fuel injection and put some really high end components to squeeze out about 450HP out of it without breaking a sweat. These suckers are used in motor yachts up to 40 feet long so I really don't understand why you'd want to put a big block in there. The outdrive is an issue but if you stick with a 350, you'll be able to just swap out the prop on your Bravo unit as the RPMs will stay the same and the unit is rated for an obscene amount of power.

      Instead of saying how can I swap the motor, ask yourself what are you trying to accomplish first. Then ask yourself what is required to get the existing equipment to get you there, or alternatively, if it can't what equipment will.
      Ships n Giggles
      1993 Bayliner 4388
      MMSI# 367412710
      Day Island Yacht Club
      Commodore

      Comment


        #4
        I’ve seen a few 2859 for sale with those engines up in Alaska. You can’t put put around at 25mph if you’re a serious fisherman and have distance to travel. They were listed for over 50k, which is not a lot if you do the math and see what they had into them. I believe the motor alone is over 20k, then add outdrive and labor. I personally would convert to outboards. There was a 2859 for sale on Vancouver Island a few years back with twin 250hp outboards on a bracket. Your other option for a similar boat is the new cut water...at around 300k.
        What boat are you looking at? I just brought up the 2859 because that one is very common for people to swap in the 496.
        Esteban
        Huntington Beach, California
        2018 Element 16
        Currently looking for 32xx in South Florida
        Former Bayliners: 3218, 2859, 2252, 1952

        Comment


          #5
          Not exactly sure what you mean by convert but you cannot modify a small block 5.7 into a 8.1 as it is a big block.

          This is what I did many years ago. Pulled both my 5.7LX engines (250hp) and sold them locally for $6,000. Bought 2 new turn key Magnum 383's, fuel injected, SmartCraft at 325 prop HP for $12,500 (yes prices have gone up quite a bit.)

          Those engines still purr like kittens as the boat is still in the same Marina as I am in now although they have about 2000hrs on them.

          Big blocks will get you more power but there is also a weight disadvantage associated with them.
          Cheers, Hans
          2007 Carver 41 CMY
          Twin Volvo D6-370
          Montreal, Canada
          Midnight Sun I Photos

          Comment


            #6
            .......... For the same money you can convert a carbureted 350 to fuel injection and put some really high end components to squeeze out about 450HP out of it without breaking a sweat....................
            In order to squeeze even near or close to 450 hp from a 5.7L SBC, the build would be incorrect for Marine Cruiser use.
            Also, the RPM at which it would produce even close to that hp would be far above what we would want to use!

            A boat needs engines that produce lots of torque, not necessarily horse power.
            The 3.480" stroke of the 5.7L SBC is just not quite enough to produce torque similar to that of a 6.3L SBC.

            IMO, the OP's best bang for the buck would be to do what Hans did (6.3L SBC), and pick up an additional .270" on the crankshaft stroke!


            The 6.3L SBC foot print is identical to the 5.7L SBC, meaning that the same exhaust components, etc, can be used.

            The Merc A drive would not be suitable.
            The final reduction will need to be changed regardless.
            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

            Comment


              #7
              the question was has anyone done this, not why,i know why i want to do this

              Comment


                #8
                Originally posted by funfishinman View Post
                the question was has anyone done this, not why,i know why i want to do this
                Originally posted by funfishinman View Post
                wondering if this is doable?
                Yes, anything is doable. What’s your budget for the conversion? You’ll need the complete 496 including exhaust and at the very least a drive ratio alteration and prop.
                Give us some details regarding your boat model, type of drive, and how you intend to use it. Is this a 20 foot sport boat or a 28 foot cruiser?
                Dave
                Edmonds, WA
                "THE FIX"
                '93 2556
                Carbureted 383 Vortec-Bravo II 2.0:1 18 1/4x19 P

                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
                  Originally posted by funfishinman View Post
                  the question was has anyone done this, not why,i know why i want to do this
                  Thread title included; costs, parts needed. Thread body asked if doable.
                  1997 Maxum 2400 SCR 5.7LX Bravo II

                  Mike

                  Comment


                    #10
                    Originally posted by funfishinman View Post
                    the question was has anyone done this, not why,i know why i want to do this
                    You posted your question on a Marine forum with quite a few members who have extensive Marine related experience.
                    Forum topics often receive more info than what was asked for.
                    Don't be surprised at answers such as what you've received.

                    Fair enough?




                    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

                    Comment


                      #11
                      One local guy had a 2850 Contessa. 350 carbed single prop. Couldn't get out of its own way. So he souped up the SBC on the advice of the local stock car racers and had nothing but grief. High rpm hp is not what you want in a heavy boat. He replaced the SBC with a 496 370 ho Volvo duoprop. 52mph! So yes it has been done with great results.
                      2007 Discovery 246
                      300mpi BIII
                      Welcome island Lake Superior

                      Comment


                        #12
                        Originally posted by funfishinman View Post
                        wondering if this is doable?
                        As long as there is room in the engine bay and stringers can support the extra weight and horsepower, then it’s doable. But not knowing what “boat” , no one can really answer that question correctly. I think that’s why the answers your getting is not what your looking for.
                        1982 3270
                        Volvo BB 140 A's
                        Killbear Marina, Parry Sound, Ontario, Canada

                        Comment


                          #13
                          I will answer your question exactly how you asked. No a 350 cannot be converted to an 8.1 therefor not doable.
                          Cheers, Hans
                          2007 Carver 41 CMY
                          Twin Volvo D6-370
                          Montreal, Canada
                          Midnight Sun I Photos

                          Comment


                            #14
                            Thread title:

                            “has anyone converted from 350 to 8.1/496 .........”

                            For me, the title clearly suggests that he is NOT wanting to turn a 350 into a 8.1!

                            .
                            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

                            Comment


                              #15
                              maybe the answers given were not what the poster wanted to hear, but they arent wrong.

                              in my opinion (as already said by Builderdude) its doable.... the parts required would be an engine and all related periphials and components to make it a complete running "marine" engine, and and complete outdrive package, from the engine flywheel back... and some modification to the hull to get everything to fit....
                              if one had a lot of patience and time to search, which is very necessary if being done on a tight budget, with used parts where acceptable, and new parts where needed, and one doing all the work themselves, i think it could be accomplished in the neighborhood of 15 to 25,000 thousand, depending on what all needs to be done to the used parts to make them acceptable for use....

                              when one lifts the engine hatch and looks in, EVERYTHING seen attached to, or required by the engine or outdrive will need to be replaced... the only thing that will remain and NOT be replaced is the hull, fuel tank, and control cables, IF they are still good... and its my opinion that if one is going thru all the trouble to make the conversion, the tank needs to be pulled and inspected, and ALL new control cables and control unit should be replaced as well...

                              and its also my opinion that after the budget job is done, the boat will likey have less value than it would with the original engine still in it and running, AND, if the re-power is not set up correctly, it will be an undependable problem child for the rest of its life....

                              to do it like it needs to be done will be expensive, without shortcuts or budget issues....

                              I agree that the cheapest and most dependable way to get more power is to bore and stroke the 5.7.... and possibly upgrade the outdrive to a duo-prop.... the boat will have a bit more value and be dependable....

                              OR..... take your many thousands of dollars, add a few more thousand to it, and buy yourself a nice turn-key boat with the power that you want.... because in the long run, it makes more sense that way.


                              NU LIBERTE'
                              Salem, OR

                              1989 Bayliner 2556 Convertible
                              5.7 OMC Cobra - 15.5x11 prop
                              N2K equipped throughout..
                              2014 Ram 3500 crew cab, 6.7 Cummins
                              2007 M-3705 SLC weekend warrior, 5th wheel
                              '04 Polaris Sportsman 700 -- '05 Polaris Sportsman 500 HO
                              Heavy Equipment Repair and Specialty Welding

                              Comment

                              Working...
                              X