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    Mercruiser 5.7 build-gctid340167

    Hi all, im considering adding a few power upgrades to my merc 350. This is a 1988 century 3500 bowrider w 315 hours. I wanna do the following..captains call exhaust, comp cam, edelbrock intake and carb package, msd ignition package which includes distributor, and maybe have heads port and polished. So my question is can the stock bottom end withstand these upgrades? Does this engine have a four bolt main? Im sure some will ask why, well I just want it to sound mean and have a little more umph..Here is a pick of the new boat

    [img]/media/kunena/attachments/vb/642711=23103-IMG_20111226_161539.jpg[/img]

    #2
    Well some questions need to be answered first.

    #1... what is your compression ratio.

    #2 ... do you have a closed cooling system.

    If the engine is the original it is most likely a four bolt main.

    For a radical sound and lots of get up and go use a comp cams # 12-236-3 but only if you have at least 9.2:1 compression. Also that is a .465 lift cam if I remember right. Some stock heads can't support that much lift without modification to the spring seats. Old vortec max of .450 lift. This is the max size cam you can put in an outdrive engine set up. You may also need run upgrade your valve springs with this cam but not sure about that

    If those aren't present use a comp cams #12-232-3 which is just above a stock cam.

    You will also want a closed cooling system to run an aluminum manifold other wise you will have a corrosion issue. If you have a closed system I would mess with the stock heads I would go with edelbrock 6089carb aluminum rpm heads but only if it doesn't raise your compression too high. It depends on which pistons you have. The carb you would want to use is a edelbrock 1409 marine carb .

    As for the ignition IMHO don't waist your money just get a goos quality marine distributor and coil. Not that an MSD system isn't good its just with this type of engine its just that you wont notice any thing at the RPM you will run. Save your money and use it on the heads or exaust.

    Next you will get a major umph in power just by going threw hull but the noise will be tiring after awhile..
    1989 Avanti 3450 Sunbridge
    twin 454's
    MV Mar-Y-Sol
    1979 Bayliner Conquest 3150 hardtop ocean express.
    Twin chevy 350's inboard
    Ben- Jamin
    spokane Washington

    Comment


      #3
      The engine over-haul or modification topic has been discussed many times here.

      There are definitely a few Dos and Don'ts when it comes to properly building or modifying the 5.7L SBC Marine engine.

      (more on that if interested)

      Is this to be in front of the Cobra or Alpha drive??

      (you mention Merc 350 and yet your signature suggests OMC Cobra)

      If Cobra, and if engine modification is considered, my first suggestion would be the Cobra to Duo Prop conversion (in lieu of engine work) in that you'd kill two birds with this idea.
      • You'd gain perform as though you increased horse power by approx 70-80 or so (which is difficult to do yet remain suitable for cruiser use).
      • You'd no longer have the drive horse power limitations of the Cobra or A drive.




      Of the members who have done this either as an OMC Cobra conversion, or a V/P upgrade....., I know of none who have disappointed.

      IMO, this would be very much worth checking into.

      Otherwise.... see some of the SBC engine related threads.

      It looks like a few of the images may not have made it over from the other forum format.

      Jeff H's thread.

      Mike Emm's first thread.

      Mike Emm's second continued thread.

      Don Enoch's thread.

      Jackoh's thread ME.com

      Scott's thread.

      Edit:

      Ditto Dave on the CCS and aluminum intake manifold. The aluminum manifold won't fair well if Raw Water cooled.

      Also note that the Dual Plane intake should be used, and not a single plane.
      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


        #4
        Thanks for the info so far, I just bought this century, it has alpha outdrive, sorry for any confusion my signature is for my bayliner. Im not sure on compression its totally stock, from what ivee read the stock bottom end will b strong enuff for mild top end build. I welcome any other suggestions.

        Comment


          #5
          You are throwing away money with most of those things. The only real return on investment as far as power for dollars is to upgrade a 2-barrel carb, if you have one, to a 4-barrel with a good manifold. That's a huge power boost. The other things like a cam are just money at the bottom of the lake.

          The Captain's Call...probably reduce power while sounding really annoying, but hey, some people like noise.

          Comment


            #6
            The Captain's Call, while going directly out, will render an improvement, as this eliminates the thru prop and below water exhaust resistance.However, and as mentioned, the noise level may drive you nuts after a while.Quite honestly, and IMO, your biggest hurdle with the OEM engine regarding a performance gain, is this:

            [img]/media/kunena/attachments/vb/642736=23104-Dished Piston.jpg[/img]Your worst enemy is this, and is spelled D E T O N A T I O Nexample piston only)

            [img]/media/kunena/attachments/vb/642736=23105-detonation piston damage.jpg[/img]And one of your better friends involves quite a bit of work, but would be this:

            [img]/media/kunena/attachments/vb/642736=23106-D shape QE Piston.jpg[/img]
            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
              Something to consider in all this is the Alpha drive is rated for a max of 300hp. I believe stock your engine is 250hp.
              Phil, Vicky, Ashleigh & Sydney
              1998 3055 Ciera
              (yes, a 1998)
              Previous boat: 1993 3055
              Dream boat: 70' Azimut or Astondoa 72
              Sea Doo XP
              Sea Doo GTI SE
              Life is short. Boats are cool.
              The family that plays together stays together.
              Vice Commodore: Bellevue Yacht Club

              Comment


                #8
                SwampNut wrote:
                You are throwing away money with most of those things. The only real return on investment as far as power for dollars is to upgrade a 2-barrel carb, if you have one, to a 4-barrel with a good manifold. That's a huge power boost. The other things like a cam are just money at the bottom of the lake.

                .

                The Captain's Call...probably reduce power while sounding really annoying, but hey, some people like noise.
                I will have to agree with most of what Carlos is saying. While wanting to do up grades unless building the bottom end to match the top end you wont see the performance you may be looking for. Keep in mind while doing this that an alpha cant support the type of power you may be looking for either.

                I will disagree with the captains call exaust maybe. When I say maybe some times marine exaust is highly restrictive so when power is left on the table due to a substandard exhaust system well then through hull exhasut will really wake it up but then if you dont have power laying around in the engine then that exaust wont do a thing for you.

                You can do a rebuild and make your boat go like a bat out hell ( how ever fast that is lol) but you are then limited by the out drive you have unless you up grade that also
                1989 Avanti 3450 Sunbridge
                twin 454's
                MV Mar-Y-Sol
                1979 Bayliner Conquest 3150 hardtop ocean express.
                Twin chevy 350's inboard
                Ben- Jamin
                spokane Washington

                Comment


                  #9
                  itsabowtime2 wrote:
                  Something to consider in all this is the Alpha drive is rated for a max of 300hp.
                  yachtman wrote:
                  Keep in mind while doing this that an alpha cant support the type of power you may be looking for either.
                  Perhaps the only saving grace is that the bow rider boats are relatively small.... meaning that the A drive may hold up.

                  Otherwise, the DP is actually what would gain you the most........... but not as easily done for an A drive boat.
                  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


                    #10
                    2850Bounty wrote:
                    Perhaps the only saving grace is that the bow rider boats are relatively small.... meaning that the A drive may hold up.

                    ottle ups I would

                    Otherwise, the DP is actually what would gain you the most........... but not as easily done for an A drive boat.
                    I have had engines with about 400 hp in an alpha drive boat but they were'nt ski boats either. What kills the alpha drive with high horse power is the going in and out of gear and the hard throttle ups not the faster speeds. I dont think it would last long in a 400 hp engine that was built for skiing. I also immediately started spinning hubs in my alpha drive with that much hp. As luck would have it that was about the time the new style of hub for alphas came out other wise I would have been out of luck.
                    1989 Avanti 3450 Sunbridge
                    twin 454's
                    MV Mar-Y-Sol
                    1979 Bayliner Conquest 3150 hardtop ocean express.
                    Twin chevy 350's inboard
                    Ben- Jamin
                    spokane Washington

                    Comment


                      #11
                      I may be a party pooper, but those through the transom exhaust systems make too much noise. IMO they are just obnoxious, and spoil the on the water experience for many. Going fast is fine if done in a neighbor friendly manner.

                      Comment


                        #12
                        To give some hard facts, I recently had to rebuild the 2-barrel 350 motor (rated at 250 HP) in my old 2455. I went to a very highly regarded marine performance shop and told him I had an open checkbook and to tell me what I should put into it. He told me to keep EVERYTHING stock except the manifold and carb. He claimed that would add 40 HP, and from the on-water testing afterward, I'd say that was absolutely true. That was for a 2-barrel to 4-barrel upgrade, if you already have a 4, then a better manifold and carb would only give a marginal improvement.

                        Comment


                          #13
                          In 1988, 5.7s rated at 260 HP had quadrajets. They may not be the best marine carb going, however, a simple carb change will not increase the HP THAT much. Theres also a performance/cost ratio.

                          As far as the open exhausts are concerned, hear this:

                          The engine is tuned for the underwater exhaust. While its possible to add the loud and obnoxious open exhausts, you would have to re-jet the carb, and really play with the distributor advance.

                          A thought here.......

                          The 1988 mercs had the thunderbolt IV system. The newer merc use teh t-bolt V. The diffreence is a knock monitoring system which increases the timing until the motor kn ocks and then backs it off ubtil it just stops. This is the optimal timing for any situation. The 5.7 with tbolt IV and a 2 BBL is rated at 230 HP. The 5.7 with a t bolt V and a 2bl is rated 250. If, by converting to the t-bolt V you can get a 20-25 HP increase, and BTW, also reduces fuel burn, it may be worth the cost.

                          What you would need:

                          The t-bolt V modules.

                          A knock sensor and the mount ( right side engine drain thingie is where its mounted)

                          some wiring fron teh sensor to the module.

                          It should be a screwdriver and wrench installation.

                          The coil and distributor sensor are the same ( and don't screw with them)
                          Captharv 2001 2452
                          "When the draft of your boat exceeds the depth of water, you are aground"

                          Comment


                            #14
                            Harv, I'm not suggesting that the Thunderbolt Ignition subtle changes do not make for more HP..... they may indeed.

                            I would want to look at the numbers before getting all excited.

                            I think that we should pay close attention to the RPM ranges where Merc rated the HP.

                            Take the new and exciting 5.7L Vortec of some years ago.

                            We'll see 315 to 320 horse power on some of these engines, and this is with the Full Dished pistons to boot.

                            Now look at the RPM where these were rated!

                            5,200 RPM in some cases....... 5,400 RPM in some!!!!!

                            Who operates their cruiser SBC @ 5,200?

                            I'd want to look at the PRM where the previous 260 hp 5.7L was rated.
                            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
                              captharv wrote:
                              In 1988, 5.7s rated at 260 HP had quadrajets. They may not be the best marine carb going, however, a simple carb change will not increase the HP THAT much. Theres also a performance/cost ratio.

                              As far as the open exhausts are concerned, hear this:

                              The engine is tuned for the underwater exhaust. While its possible to add the loud and obnoxious open exhausts, you would have to re-jet the carb, and really play with the distributor advance.

                              A thought here.......

                              The 1988 mercs had the thunderbolt IV system. The newer merc use teh t-bolt V. The diffreence is a knock monitoring system which increases the timing until the motor kn ocks and then backs it off ubtil it just stops. This is the optimal timing for any situation. The 5.7 with tbolt IV and a 2 BBL is rated at 230 HP. The 5.7 with a t bolt V and a 2bl is rated 250. If, by converting to the t-bolt V you can get a 20-25 HP increase, and BTW, also reduces fuel burn, it may be worth the cost.

                              What you would need:

                              The t-bolt V modules.

                              A knock sensor and the mount ( right side engine drain thingie is where its mounted)

                              some wiring fron teh sensor to the module.

                              It should be a screwdriver and wrench installation.

                              The coil and distributor sensor are the same ( and don't screw with them)
                              You mention upgrading to the Thunderbolt 5 ignition system, what about upgrading to something like the MSD system, which comes with their distributor/ coil and ignition control module? below is the link...

                              [U]http://www.keitheickert.com/p-13520-...tall-deck.aspx

                              Comment

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