Dry-Joint Exhaust ??

Discussion in 'General Discussion' started by 37 Dancer, Jan 6, 2009.

  1. 37 Dancer

    37 Dancer New Member

    351
    Oct 6, 2006
    South Shore , Long Island
    1995 Sea Ray 370DA
    7.4 EFI's
    My risers and manifolds on my Merc 7.4's.... are over 4 years old .... and are starting to look a bit ratty. My mechanic suggested they be replaced this spring and mentioned a Dry-Joint system.

    Anyone change over to the new system ?

    How does it work ?


    I did a search......very little info out there.


    Thanks
     
  2. fc3

    fc3 Just another eclectic geek TECHNICAL Contributor

    Nov 12, 2006
    Northern NJ
    1999 Sea Ray 330DA
    Twin 7.4 MPI (310 propshaft HP) V-drives
    Twin Mercury Marine marinized 7.4L L-29 V8s
    Cast iron block w 4-bolt mains
    The joint between the manifold, elbows, and risers if any, usually have an exhaust passage and two to four water passages around the exhaust passage. A gasket fault could cause water ingestion. Dry joints don't have the water passages. Water is routed from the manifold to the elbow via a hose.

    Best regards,
    Frank
     
  3. Jimmy Buoy

    Jimmy Buoy Well-Known Member

    Dec 3, 2008
    Sarnia, Ontario, Canada
    340 Amberjack
    twin 8.1S 370 Hp + 4.5 Westerbeke Genset
  4. J Levine

    J Levine New Member

    753
    Oct 5, 2006
    New Jersey
    1995 Sea Ray 370 Sundancer
    Mercruiser 7.4L Blue Water inboard V Drives
    You cant retrofit the dryjoints onto a 454 big block because the exhaust manifolds are different. The dry joint design came out after the 454 went out of production. If I was running small blocks I would switch over but with a 454 it can't be done. I looked into trying to use dry joint risers and elbows with the old 454 manifolds and it just doesn't look like they would line up. I have even thought about replacing my crappy Merc exhaust system with Crusader parts because their design looks so much better.
     
  5. fc3

    fc3 Just another eclectic geek TECHNICAL Contributor

    Nov 12, 2006
    Northern NJ
    1999 Sea Ray 330DA
    Twin 7.4 MPI (310 propshaft HP) V-drives
    Twin Mercury Marine marinized 7.4L L-29 V8s
    Cast iron block w 4-bolt mains
    Guess I'm not the only one considering Crusader parts the next time around. I measured the Crusader manifolds and elbows on a friends big blocks. Pretty close, but would have had to change some other exhaust plumbing around, so I didn't do it. Maybe next time.

    I think you could use block off gaskets on the manifolds and elbows, pull the plugs and insert nipples and hoses, which might help things a bit, but I doubt it would make much difference. The top of the manifold still has those damned holes.

    Best regards,
    Frank
     
  6. 37 Dancer

    37 Dancer New Member

    351
    Oct 6, 2006
    South Shore , Long Island
    1995 Sea Ray 370DA
    7.4 EFI's
    JL.......Your saying that the dry joint system is not available for Merc 7.4's ??

    My mechanic is a knowlegable Merc guy.......He told me he can get the system for my motors......but I will call him in the AM......to verify.

    Maybe they're in production at this time ??

    I'll report back when I find out the facts.............
     
  7. LMBoat

    LMBoat Member

    412
    Oct 4, 2006
    Ft Lauderdale
    1999 450 EB
    Cummins 6CTA's
    Wonder if anyone has tried welding up the holes on both manifold & elbow and decking the part to make a dry connection?......
     
  8. douglee25

    douglee25 Well-Known Member

    Jan 13, 2008
    NJ
    Boatless
    Big ones!
    The problem with that is the pieces are usually cast. Welding cast to be water tight isn't easy. It can be done, but parts usually have to be preheated and it still doesn't work too well.

    Doug
     
  9. 37 Dancer

    37 Dancer New Member

    351
    Oct 6, 2006
    South Shore , Long Island
    1995 Sea Ray 370DA
    7.4 EFI's
    Ok......spoke to my mechanic this morning......he said he has done the dry-joint system on a few different motors ( V6 & V8 ) ...the most recent was last month......on a pair of Merc 8.1's.....he assumed they were available for my 7.4's...when he mentioned it to me......but will call Merc and find out availability.


    So ..... it may end up to just replace the risers and manifolds with the standard system :(
     
  10. fc3

    fc3 Just another eclectic geek TECHNICAL Contributor

    Nov 12, 2006
    Northern NJ
    1999 Sea Ray 330DA
    Twin 7.4 MPI (310 propshaft HP) V-drives
    Twin Mercury Marine marinized 7.4L L-29 V8s
    Cast iron block w 4-bolt mains
    Also check that they are Mercruiser parts. You do not want Osco, GLM, or one of the other after market exhaust systems. There is a reason that they cost less and it's not because they're nice guys who are willing to forgo making a profit.

    Best regards,
    Frank
     
  11. J Levine

    J Levine New Member

    753
    Oct 5, 2006
    New Jersey
    1995 Sea Ray 370 Sundancer
    Mercruiser 7.4L Blue Water inboard V Drives
    I fear that your mechanic will find that while the dry joint risers and elbows are available becuase they are also used on the small blocks, dry joint manifolds for the 454 are not available.
     
  12. boatrboy

    boatrboy Active Member

    Oct 3, 2006
    Orange, CT
    1999 270 Da
    7.4 MPI w/B3
    I spent time with the Mercruiser rep at the NY boat show going over this very issue. He spent 20 minutes on his computer and confirmed to me that the dry joint is NOT available for my 7.4. He said the exhaust manifolds/heads are different for the 8.1. I have not personally verified this, but he seemed knowledgeable. He explained the differences of the old vs new dry joint set up on the "cut-away" models at the show. I have not investigated a replacement any further, as it was mostly curiosity for me at this point.

    Mark
     
  13. J Levine

    J Levine New Member

    753
    Oct 5, 2006
    New Jersey
    1995 Sea Ray 370 Sundancer
    Mercruiser 7.4L Blue Water inboard V Drives
    There is very little in common between the 7.4 and the 8.1.
     
  14. LUNASEA275

    LUNASEA275 New Member

    6
    Sep 16, 2009
    Patchogue, NY
    370 Sundancer 1999
    7.4 MPI 380 HP 454's
    I would have also loved to switched from the standard mani./risers and gone to the dry Joint and also being told that they do not exist for the 7.4 454's. If anyone hears different, please advise. The original design from Merc should have triggered a class action law suit. The fact that riser gaskets have to be checked or changed every 2-3 seasons is absurd and should have been recalled. :smt013
     
  15. Nehalennia

    Nehalennia Well-Known Member

    Aug 22, 2007
    Marysville, WA
    2001 310DA twin 350 MAGs, Westerbeke 4.5KW
    Twin 350 MAG V-drives
    You can see the round ports on the left and right of the main exhaust chambers in this image.
    [​IMG]
    and they mate up with the matching ports on the elbows or risers passing through to the elbows
    [​IMG]
     
  16. Jimmy Buoy

    Jimmy Buoy Well-Known Member

    Dec 3, 2008
    Sarnia, Ontario, Canada
    340 Amberjack
    twin 8.1S 370 Hp + 4.5 Westerbeke Genset
    I'd be getting a bit concerned about your mechanic's statements. He's recently converted to a dry-joint exhaust system on a Merc 8.1?:huh:

    The 8.1's original design encorportated a dry-joint exhaust system since their inception!:smt101 So... it wouldn't be much of a trick to do that now would it?

    Perhaps you missunderstood his claims.
     
  17. LUNASEA275

    LUNASEA275 New Member

    6
    Sep 16, 2009
    Patchogue, NY
    370 Sundancer 1999
    7.4 MPI 380 HP 454's
    The 8.1's are a different block than the 454 7.4. It is also my understanding that my 380HP motors also utilize 502 Heads to gain the extra HP. All in all, I am hope to find some retrofit that allows the dry-joint system for the 7.4 380 HP blocks.
     
  18. M Prod

    M Prod Active Member GOLD Sponsor

    547
    Oct 6, 2017
    North Vancouver, BC
    2005 Sundancer 340
    Aquapro Dinghy w/ Honda 8hp
    Kohler 5KW Genny
    Raymarine Electronics
    8.1 Horizons /V Drives
    I know this is a very old thread, but I have a question about the dry joints. I just purchased my '05 340 in the fall (8.1s), and before purchasing confirmed the manifolds were in fact cast iron and not aluminum. The broker I bought the boat from told me I don't have to worry about water getting into the engine through corroded manifolds/risers since the dry joint system is in place. That said, having had experience with water getting into the engine through corroded manifolds on previous boats, I still worry. I understand the layout and makeup of the dry joints, but the manifolds will still corrode and could still fail seeing as they are raw water cooled (the boat is in the salt) correct? I have no idea how old the manifolds are on the boat right now, but should I just go ahead and replace them for peace of mind? Do I need to worry? Thanks for any and all feedback.
     
  19. douglee25

    douglee25 Well-Known Member

    Jan 13, 2008
    NJ
    Boatless
    Big ones!
    Dry joint vs. Wet joint are completely different in design. The water passage for wet joint exhaust is right at the connection between the riser and manifold. The water passage for a dry joint setup comes from an offset connection several inches back from the joint itself. The wet setups fail when the small sealing area corrodes and then water drains back down to the cylinders. You just don't have those issues with a dry joint setup.

    The only thing I may consider with a dry joint setup is to install a flush system for salt water applications. Otherwise, run it and enjoy.

    Take a look here. It should be much more apparent - http://www.mooreperformance.info/Mercruiser-V6-manifold-kit-2002-2003-2004.html

    Doug
     
  20. M Prod

    M Prod Active Member GOLD Sponsor

    547
    Oct 6, 2017
    North Vancouver, BC
    2005 Sundancer 340
    Aquapro Dinghy w/ Honda 8hp
    Kohler 5KW Genny
    Raymarine Electronics
    8.1 Horizons /V Drives
    Thanks Doug. I do have an on board intregrated flush system, and will continue to use it. Much appreciated.
     

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