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Manifold plumbing

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  • Manifold plumbing

    So I'm replacing my manifolds and risers on my 20'er, 5.8 PMC, thinking about doing some replumbing, I'm hoping to get some insight on what's the best inlet to use. I'm sure ones has to be better then the other. Which would you recommend? First picture I can go into the back of the manifold, second picture I have 2 location on the manifold and 1 on the riser.
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    Last edited by Striper Sniper; 08-13-2022, 12:09 PM.

  • #2
    The one on the riser is if you intend to include the manifolds in the FW side. Which ever one is easiest to work on in the manifolds.
    1988 26' cuddy
    1975 20' open
    16' Sandpiper
    14' Certified Fiberglass

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    • #3
      Originally posted by Quik Fix View Post
      The one on the riser is if you intend to include the manifolds in the FW side. Which ever one is easiest to work on in the manifolds.
      Good point. I forgot to mention it's a fresh water cooled system.

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      • #4
        Pat, remember that there are 2 freshwater system types. A half system(only the block is cooled) and a full system(block and manifold cooled). The full system requires a larger heat exchanger than the half.
        Atlantic City, NJ
        1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

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        • #5
          Originally posted by Ship View Post
          Pat, remember that there are 2 freshwater system types. A half system(only the block is cooled) and a full system(block and manifold cooled). The full system requires a larger heat exchanger than the half.
          Another great point, thanks Skip! Mine is a half cooled system. Raw water cools the exhaust. Would you stay with the risers or plumb it into the manifolds?

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          • #6
            Your heat exchanger is prrbablyl the smaller so only do the block. Do the riser and manifolds with raw.
            Atlantic City, NJ
            1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

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            • #7
              Originally posted by Ship View Post
              Your heat exchanger is prrbablyl the smaller so only do the block. Do the riser and manifolds with raw.
              Correct, the heat exchanger is smaller and only cools the block. Raw water cools the exhaust. With that being said, logically to me anyway the longer the cool raw water is in the system the better. I'm thinking the top or front inlet of the manifold makes the most sense.... would you aggre?

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              • #8
                Pat, I can't find my circulation diagram but at the very least the hotter water won't cool the exhaust hose and any fiberglass pipe that is near the risers. Anything beyond 200* is a threat to the hose and pipe. Exhaust gas will melt the hose and or the resin.
                Atlantic City, NJ
                1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

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                • #9
                  Or that is my understanding.
                  Atlantic City, NJ
                  1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

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                  • #10
                    Click image for larger version

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ID:	35637 The gaskets you used for the riser to manifold joint will dictate if you can go with a full FW system or not. Forget all the thermostat stuff on the GM base. You get the picture.
                    1988 26' cuddy
                    1975 20' open
                    16' Sandpiper
                    14' Certified Fiberglass

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                    • #11
                      Pleasurecraft ran them to the rear of the exhaust manifolds only because they are closer to the heat exchanger's outlet -Hose below


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                      • #12
                        The other thing is make sure the raw water hoses going to the manifolds are the same length. I thought I would clean things up where the raw water teed for each side.No. It all went to the short side.
                        '78 20ft Cuddy
                        Mercruiser 350 FWC preVortec w/Carb

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                        • #13
                          Originally posted by Pedlyr View Post
                          The other thing is make sure the raw water hoses going to the manifolds are the same length. I thought I would clean things up where the raw water teed for each side.No. It all went to the short side.
                          Oh shoot thats an issue now I have to rework it all over again.

                          Danm and I thought I was over the hump, apparently not so.
                          Last edited by Striper Sniper; 08-13-2022, 08:42 PM.

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                          • #14
                            Pat, what Ed says is 100% right on. Equal to both sides is a must.
                            1988 26' cuddy
                            1975 20' open
                            16' Sandpiper
                            14' Certified Fiberglass

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                            • #15
                              They are not the same length on the PCM system - are you guys saying that's wrong? It's not even the same length on their raw water systems

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