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4.3 Performance Boost?

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  • 4.3 Performance Boost?

    Hey guys, I love reading this site, and look forward to reading your opinions...I own a 1986 Wellcraft 19'3" Open Bow with a 175hp 4.3 liter (2 bbl) chevy OMC Cobra setup. Now.. I want to maximize performance.This summer I bought a torque-shift prop. MAN! Great for skiing (11p-26p), though the boat is semi-underpowered, so I have to trim it high enough to cavitate in order to up-shift.. Top speed was not really effected ~43-44 mph (according to my speedo). I've been contemplating converting to a 4 bbl, which I've seen for ~$400 carb + manifold. Will this improve Bottom end and top end? Recommend this or a 305 v8 swap? Fuel economy is an issue with a 25 gallon tank....Thanks!


  • #2
    Re: 4.3 Performance Boost?

    4 bbl and edlebrock intake, read the post "Its been 3 months but she is like new"

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    • #3
      Re: 4.3 Performance Boost?

      Have you ever heard of anyone using a "Carb-Spacer"??see http://cfm-tech.com/ ?? They claim 15hp-30hp for $100.Does an Edelbrock intake offer more performance than a stock 4 bbl intake?Thanks..

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      • #4
        Re: 4.3 Performance Boost?

        i dont want to get the omc guys mad but keep in mind that with omc gone it is harder to get outdrive parts and the drive may not hold up as well if you start pushing a lot more power through ittommays
        If a dirty bottom slows you down what do think it does to your BOAT

        1970 Cal 29 Sea Fever
        http://cal29seafever.blogspot.com/
        1981 J24 Tangent 2930
        http://s565.photobucket.com/albums/s...%20for%20sale/
        Tommays
        Northport Ny

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        • #5
          Re: 4.3 Performance Boost?

          I doubt if adding a four barrel onto a stock six cylinder is going to give you much more horsepower. If you can get the engine to "flow" better then perhaps it would make sense. If you REALLY want to get more from this engine, I would suggest sending the heads off to someone like Lingenfelter Engineering for porting work, then install a new manifold and four barrel. Thru hull exhaust would also help. While added horsepower will be putting more strain on your outdrive, the cobra should be able to handle up to 275 horse (the King cobra up to 330 horse).

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          • #6
            Re: 4.3 Performance Boost?

            Sorry to double post....but after reading some of the other threads about "hopping up" v-6's I had to add a few things. I am happy for the guys that are so excited about their "new" engines that have been bored 60 over, have high compression pistons, high lift cams....etc. All of that stuff is great FOR A STREET ROD...NOT A BOAT. Unless you plan on only running your boat wide open for a few secounds at a time this is a disaster waiting to happen. Boring a small block 60 over is risky enough, if it doesn't crack, you better have closed cooling or never take it in salt water, your cooling passages will be so thin any corrosion will lead to block failure.

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            • #7
              Re: 4.3 Performance Boost?

              I would say that a 4 bbl will make matters worse. that motor is already set up for top performance. that motor has to be able to handle the extra gas or it will just load up and smoke a lot. you get extra horse power from your cam ,your heads and your carb. but they have to be set up. the last motor that I rebuilt last summer was a 429ci and it had a 2 bbl. I bored it out to 30 over to just clean the cylinders but i put a Edelbrock performer intake and 600 cfm edelbrock carb to match. i then put in a bigger cam to hold the valves open longer and different heads with bigger valves to give it more gas. the engine had plenty more power after that. evertime you droped the clutch it would twist a drive shaft. i have a 305ci in my boat and thought about building it up. i love those small block chevys.

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              • #8
                Re: 4.3 Performance Boost?

                What kind of carb is stock on a 87 Merc 4.3? I am thinking about trying out some of those carb spacers. Edit:How hard is to switch to thru-hull exhaust? The performance would be nice and I love the sound of them much better.
                Don't fear the Rinker!

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                • #9
                  Re: 4.3 Performance Boost?

                  Carb spacers are a funny thing...sometimes they work great, other times zero imprvement. The only way to find out is to try one. As for thru hull on a 4.3 - you will get ZERO improvement. Put the money into something else.
                  The last time religion controlled the world it was known as the Dark Ages

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                  • #10
                    Re: 4.3 Performance Boost?

                    Thanks bomar. I was wondering if exhaust would help a v6, actually, i wonder what a v6 would even sound like with thru hull, it may not even sound that great. What kind of carb is on my motor? The spacers are for holley, rochester..etc..
                    Don't fear the Rinker!

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                    • #11
                      Re: 4.3 Performance Boost?

                      The v-6's don't really sound too great w/ thu hull.You would get a performance benefit from going to an Edelbrock intake and a marine 4 bbl....but I don't think I would do it.For the $$$ invested you would pick up very little speed. It takes 12-18 HP to gain 1 mph in a boat. I think a better choice would be to prop it correctly with a good Stainless Steel prop (like a Merc Mirage), keep the bottom clean, DO NOT wax the bottom of the hull (at least not the last 4-5' of it), and keep you eyes open for a good deal on a boat with more cubes under the hatch.There is no subsitute for cubic inches.
                      The last time religion controlled the world it was known as the Dark Ages

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                      • #12
                        Re: 4.3 Performance Boost?

                        I forgot to add....A 305 would be a very poor choice to swap.It's external dimensions are the same as a 350.....and has just about ZERO methods of gaining HP compared to a 350.
                        The last time religion controlled the world it was known as the Dark Ages

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                        • #13
                          Re: 4.3 Performance Boost?

                          Why not wax the bottom of the hull? Next spring I'm going to put a good buff job and teflon coat on it to restore some shine.
                          Don't fear the Rinker!

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                          • #14
                            Re: 4.3 Performance Boost?

                            Wax on the area of the hull that is wet when on plane will slow the boat.It's well documented in the perfomance boat world.Abrading that area will actually gain speed.
                            The last time religion controlled the world it was known as the Dark Ages

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                            • #15
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                              Re: 4.3 Performance Boost?

                              How come you don't want to wax the last 4 or 5 feet of the boat hull?

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