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  • Marine exhaust

    My question is what grade of stainless would people use for a saltwater injected marine exhaust system. This will be a replacement for the original that was built many years ago out of mild steel. I have been getting mixed answers 304 versus 316. 316 sounds to have a greater resistance to saltwater unless the SW is warm. This system has a SW injection pump to cool the exhaust before leaving the exhaust manifold. Any input?

    Thank you,

    Dieselbreath

  • #2
    Boats generally have cast iron manifolds, even today. Stainless silent choice systems up top, and an aluminum Y pipe to divert the exhaust down thru the out drive.

    So I wouldn't worry too much about the grade.

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    • #3
      Yes for the 304 SS. I am not sure about the Sulfur in the 416. Also the 416 will rust a little bit.

      Kevin
      [XMT 350MPa , XR Feeder & Aluma Pro gun , Dynasty 200DX]

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      • #4
        dont plum sea water though your hot manifold

        Originally posted by Dieselbreath View Post
        My question is what grade of stainless would people use for a saltwater injected marine exhaust system. This will be a replacement for the original that was built many years ago out of mild steel. I have been getting mixed answers 304 versus 316. 316 sounds to have a greater resistance to saltwater unless the SW is warm. This system has a SW injection pump to cool the exhaust before leaving the exhaust manifold. Any input?

        Thank you,

        Dieselbreath
        i have seen a perkins manifold pluged solid with salt it cost the guy a compleat over haul you should run your fresh water system though it then to your heat exchanger , thats were your sea water should be . just to cool your fresh water . as far as stainless for your manifold i would think the heat could bake the silver or nickel and it would look like ss headers after a while . i would use a factory marine manifold and use zinks in you sea water side of you heatexchanger the zincs are for rust controll it gives a place for electrolisis to go befor it can eat block or manifold hope this saves you time and money

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        • #5
          Originally posted by Dieselbreath View Post
          My question is what grade of stainless would people use for a saltwater injected marine exhaust system. This will be a replacement for the original that was built many years ago out of mild steel. I have been getting mixed answers 304 versus 316. 316 sounds to have a greater resistance to saltwater unless the SW is warm. This system has a SW injection pump to cool the exhaust before leaving the exhaust manifold. Any input?

          Thank you,

          Dieselbreath
          DUDE....if it ran many years with mild steel () then ANY stainless will be just fine.
          That said I have yet to see any mild steel exhaust on a boat, fresh or saltwater. So it is either homemade or you are possibly mistaken. Mild steel would be absolute crap.
          If you have pics we could possibly be more helpful.

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          • #6
            It is very much home made. It is on a 50' square rig sailboat that a family friend of mine built about 15yrs ago. It has a non pressurized fresh water cooling system. I don't know much more about it. I haven't even seen the boat in person. The exhaust is in my shop. Hope to get something put together in the near future.

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            • #7
              I work on boats a LOT.(99%) That is not saying I am an expert. Most of the closed cooling systems I recall used seawater for the exhaust and the rest of the engine components were included in the closed/freshwater system.
              No telling what they were doing on a homemade system. If you could look over what they had by checking out the entire boat, you may be able to improve on the entire thing considerably.
              It would be nice if you had a scrap cylinder head of the same make/design that you could fab off of on the bench. You are gonna need some really thick flanges and need a way to insure it is leak free along the way as it should be double walled. Once you do the outer wall, some areas will be inaccessable. I am sure you have considered that, but brought it up, just in case.

              www.facebook.com/outbackaluminumwelding
              Miller Dynasty 700...OH YEA BABY!!
              MM 350P...PULSE SPRAYIN' MONSTER
              Miller Dynasty 280 with AC independent expansion card
              Miller Dynasty 200 DX "Blue Lightning"

              Miller Bobcat 225 NT (what I began my present Biz with!)
              Miller 30-A Spoolgun
              Miller WC-115-A
              Miller Spectrum 300
              Miller 225 Thunderbolt (my first machine bought new 1980)
              Miller Digital Elite Titanium 9400

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              • #8
                The main thing is what ever system your using ,down hill from were the salt water is introduced stainless isn't much better then mild steel because the problem is the inside of the system being worn down by the abrasives in the salt water. If your introducing the salt water after the exhust monifuld make sure you have a 180 elbow between the too, with as much elevation as possable. So the salt water can't get back into the motor when your healed over.

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