Long run exhaust and efficiencies

Discussion in 'Diesel Engines' started by tranmkp, Mar 9, 2012.

  1. tranmkp
    Joined: May 2002
    Posts: 93
    Likes: 2, Points: 0, Legacy Rep: 78
    Location: Texas

    tranmkp Junior Member

    I have a 70hp Westerbeke running a 2 inch out of the manifold to a Vernal lift. 2 inch discharge out of vernal for about 15 feet to transom.

    Question,

    Will I get better performance if I go to a 3 inch?

    Will I get better acoustical/engine performance going to a larger muffler?

    Boat is displacement and cruises at 2600 rpm.

    What I mean by performance is better flow characteristics.

    I have a feeling I may be getting too much back pressure.

    There is the possibility of having a custom step up header made from the manifold 2in to 3in.
     
  2. MechaNik
    Joined: Jan 2011
    Posts: 139
    Likes: 5, Points: 0, Legacy Rep: 62
    Location: Greece, Italy

    MechaNik Senior Member

    If you are concerned about your back pressure then you should start by measuring it. Also try to get some exhaust valve temperatures if you can.

    What is the height above the "Vernalift" Muffler? If it is substantial it will cause unnecessary back pressure.

    Normally I would say the next step in an improved system would be a water seperator. Going for to big a pipe diameter on a bigger wet lock muffler could cause back flooding as the water may not clear the muffler.
     
  3. gonzo
    Joined: Aug 2002
    Posts: 13,621
    Likes: 383, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    A too large exhaust pipe will have more water than the muffler can accept. If that happens, the water will back into the engine.
     
  4. Petros
    Joined: Oct 2007
    Posts: 2,936
    Likes: 139, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    There will not be a noticeable improvement in power going from 2 inch to 3 inch on a 70 hp engine, and it will make a lot more noise. use a performance muffler would be better investment I suspect.

    What makes you think you have too much back pressure?
     
  5. MikeJohns
    Joined: Aug 2004
    Posts: 3,176
    Likes: 198, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    The real question is what is the pressure at the exhaust manifold.
    It's very easy to determine with a simple clear tube water filled manometer the only hard part is tapping into the manifold or exhaust close to the engine ( past the turbo if turbo charged). You only need tap an 1/8 inch pipe fitting and afterwards fit a std plug.
     
  6. mydauphin
    Joined: Apr 2007
    Posts: 2,164
    Likes: 52, Points: 48, Legacy Rep: 575
    Location: Florida

    mydauphin Senior Member

    You really have to measure as stated by others. 2 inches is about for 7 hp diesel , but running it 15 feet is a different problem. You sure you can go somewhere else shorter with exhaust, perhaps even a dry exhaust?
     

  7. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 109, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    Will I get better performance if I go to a 3 inch?

    What IS "better performance"?

    Going from 1.4 gph to 1.38 gph in cruise might take a long time to justify the expense.

    FF
     
Loading...
Similar Threads
  1. Gashmore
    Replies:
    21
    Views:
    2,165
  2. Frosty
    Replies:
    242
    Views:
    36,412
  3. Chris Bretter
    Replies:
    47
    Views:
    21,785
  4. markstrimaran
    Replies:
    5
    Views:
    1,112
  5. Lemans
    Replies:
    26
    Views:
    4,682
  6. marsh trapper
    Replies:
    2
    Views:
    1,370
  7. ianeye
    Replies:
    4
    Views:
    3,824
  8. SURRYEQUIP
    Replies:
    15
    Views:
    2,804
  9. Easy Rider
    Replies:
    19
    Views:
    10,798
  10. DennisRB
    Replies:
    3
    Views:
    8,305
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.