3 Inch, 4 Inch, 2, 3 Inch?

Sporting her original single 3 inch pipe

The Special V8 is in WECATCHEM and all lined up. And now the big question. Single exhaust or duel exhaust? I am inclined to keep her single since duel exhaust would not have been an option then. But increasing the copper pipe to a 4 inch? Is that what the Scrips would have had? I am also not to thrilled about adding another hole so close to the original one? Twin K’s look?

Pre War sportsman with twin K’s


Duel 4 inchers?

4 pipes?

Thats gonna make a splash


Monster pipes

Thats a whole lotta pipeage

jim Staibs got Pipes

But, hell, I needed a story today and this of course is one of those stories that has no real correct answer, so have at it in the comment section.


34 replies
  1. Steve in the woods
    Steve in the woods says:

    2 into original pipe, that will be the Sound! BTW, you do not know what pollen is…

  2. Gary Van Tassel
    Gary Van Tassel says:

    It is a back pressure thing. 350’s need to breath. remember it is not just exhaust going out the pipe(s) but cooling water as well. No comparison to automotive exhaust sizing so don’t be fooled. At least 2 x 3″. 2 x 4″ better. Combined area of exhaust pipes (if two into one) must not be less than the total area of the manifold discharges. I assume no muffler so that helps with back pressure. Be a shame to go all this way for power to just choke it off at the tail end. Finally, don’t ignore air in. More times than not when I check I find a slight vacuum inside the top of the engine box. FYI, the engine compartment on the Kavalk (low end 350) pulled negative pressure at full power. Opened up a couple to unobtrusive vent holes into the cockpit to get more air into the engine.

  3. Max Mueller
    Max Mueller says:

    For what it’s worth, (0) I agree with Van Tassel. When I owned an 18 ft Century, I replaced the inline L head Gray Marine Continental with a CC 327Q and cut the hole off center to match existing exit. At wide open throttle when viewing exhaust it appeared to me to need every bit of that additional breathing and that engine installation ran very well.

  4. Max Mueller
    Max Mueller says:

    Wecatchem’s exhaust exit appears to be centered in the transom in the image. If so, perhaps use single large pipe using Van Tassel’s combined area computation.

  5. MikeS
    MikeS says:

    Single 3-1/2” has more cross sectional area than two 2-1/2” pipes that would have been on original Chris 350

    • Sunday Funday
      Sunday Funday says:

      It’s actually the other way, but they are very close to the same size.
      3.5″ = 9.62 sq in
      2.5″ = 4.9 x 2 = 9.81 sq in

      Somebody please check my math as it’s been awhile!

      • MikeS
        MikeS says:

        You’re right. 4.90 registered as 4.09 in my head. Should have had my 9 year old do the math for me.

  6. Steve Anderson from Michigan
    Steve Anderson from Michigan says:

    This discussion brings up another question, where does the white stripe belong? A couple of inches above the water level on an empty boat at rest? With a stock CC V8 without any risers, where should the pipes come out in relation to the water level?

  7. Mike Stevens
    Mike Stevens says:

    It appears the math might be the winner for the engine to run correctly. Also, Matt, gotta love reading your notes. Duel is a contest between two competitiors (old style with with pistols) and dual means two! Hope this arguement doesn’t end with a duel and that the boat does end up with dual exhausts!

  8. C Stang
    C Stang says:

    We are in the process of adding a 350 to a Lyman 23. Manifolds were 3-inch so we expanded the thru-hulls to 3-inch as well. We used bronze as we run in salt water.

  9. Ron in Seattle
    Ron in Seattle says:

    Single exhaust, keep the original look. Who cares if you lose 2 MPH at top speed? Who runs at top speed? Picture shows what Chris Craft used in there twin V-8 cruisers to have dual exhaust, and the installation in my 20’ CC custom.

  10. Karl Hoffman
    Karl Hoffman says:

    Chris Craft recommended 3-1/2 in for the 283 with single exhaust. What is the current size on Wechatchem? Its easy to enlarge the current exhaust size. Remove the old pipe screw a piece of wood to the inside of the current hole so your hole saw has a something to center on and drill from the outside to the appropriate larger size.

  11. Mike U
    Mike U says:

    For you – I recommend three pipes. The single, dual & quatro have all been done before, but not three & you won’t have to replace any transom boards. Besides, you’re a bit odd as well.

    • Troy in ANE
      Troy in ANE says:

      Dang! Mike U hit the nail on the head.

      I was going to say Dual since I like them, but triple would be an ongoing conversation piece. You could take each manifold to outboard discharge and Y or T both to the off-center current discharge. That should give plenty of breath to the engine.

      It’s surprising how good a flat head six sounds when T’ed through 4″ cooper to dual exhaust.

  12. don vogt
    don vogt says:

    FWIW, Miss arrowhead, for example, with the a120 v8, had two exhausts,equally spaced on either side of the center line of the transom. dont seem to be able to send picture.

    Like star dust or gotta woody, pictured above.

  13. Brian Robinson
    Brian Robinson says:

    Matt, for the record, if you Y-pipe a small-block into your single 2 3/4” stock pipe it will breather fine. It is a sacrifice of maybe 10hp vs. dual exhaust. We did this very same experiment on our 22’ Gar Wood several years ago with big-block 440 Chrysler going from two 3” pipes to a stock configuration single 3” pipe. Boat sounds great, a little quieter than before, and very little, if any, power loss.

    A couple other notes:
    The Scripps boats used a 3 1/2” pipe

    The W went from a 2 3/4” pipe to a 3 1/2” pipe when it became the WB.

    All M variants went from 2 3/4” to 3 1/2” I’m mid-1948

    The 28’ Gar Wood you show named Liberty has stock twin 5” pipes.

  14. Mark
    Mark says:

    You should go back to the W. That way you don’t have to worry about back pressure or exhaust size when being towed.

  15. Dick Dow
    Dick Dow says:

    I’m going through the same question as I am installing a 454 into the Red&White. Do I simply retain the diameter that the Royal used, go dual or raise the gas tank so I can increase the diameter? Then there is the muffler issue as this application has them below the waterline and everything I’ve seen that would fit is qualified as “not for below waterline installation”…

    Matt, for “Wenatchem”, Ron is correct – use the standard Chris collector and size the pipe and outlet accordingly.

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