Ported X head 340 header size?

Mopar Exhaust Systems

  1. midnight340

    midnight340 FABO Gold Member FABO Gold Member

    Messages:
    412
    Likes Received:
    245
    Joined:
    Mar 19, 2014
    Location:
    Lawrence, KS
    Local Time:
    8:46 AM
    Hey All, just a question that some of you might have an opinion on. (there are some opinions here if I recall.) :D

    My 340 is pretty well sorted at this point, tuning etc. I have a true 9:1 motor, Lunati solid .526/.546 lift cam, port-matched LD340, big Thermoquad, etc. Cope built 518 OD with 4.10's.
    My heads were ported/polished and really worked over by Bob Mullen way back in the day. (apparently he designed the W-2 heads?) I've been running 1-5/8" mid length headers that I made from some long tube ones years ago. My question is about what size primaries you guys might suggest. (I expect some differing opinions, but that's fine.)

    Since I can't do advanced math to figure port area, I took some used header gaskets and carefully formed some wire to the port outlines, then rebent the wire into a circle and it came out at exactly 1-7/8" I.D. I'm thinking that's a lot to try to run into 1-5/8" (...even though I did do some port-matching so there's no sharp edge dam, but it's more of a rounded transition.)

    Fitment not an issue as I may make my own, or am game to modify some existing ones. Street/strip use. Ideas???
     
  2. brian6pac

    brian6pac Well-Known Member

    Messages:
    4,919
    Likes Received:
    3348
    Joined:
    Nov 15, 2016
    Location:
    N.E.Ohio
    Local Time:
    9:46 AM
    I have always run 1 7/8" and they let the motor rev nice, 7600 and still pulling.
     
  3. Oldmanmopar

    Oldmanmopar Going left turning right FABO Gold Member

    Messages:
    8,994
    Likes Received:
    5448
    Joined:
    Jan 8, 2009
    Location:
    Danielsville Pa. 18038
    Local Time:
    9:46 AM
    If your using factory heads 1 7/8 for a 202 208 valve 340. 1 3/4 for a 188 valve 340-360 or a small cam 202. 1 5/8 for a 318-273.
     
  4. RustyRatRod

    RustyRatRod Lemmie see your b00bs. FABO Gold Member

    Messages:
    67,610
    Likes Received:
    41811
    Joined:
    Jun 7, 2010
    Location:
    Georgia
    Local Time:
    9:46 AM
    My attitude has always bee run as big of a primary tube as will fit. Period.
     
    • Agree Agree x 2
    • tubbedamx

      tubbedamx Location Boise, Idaho

      Messages:
      650
      Likes Received:
      94
      Joined:
      Jan 7, 2007
      Location:
      Boise, Idaho
      Local Time:
      7:46 AM
      If you don’t already have it get the motor trend app. $5 a month Lots of mopar content.

      engine masters has been testing headers lately on a 450hp sbc.

      My vote would be 1 3/4 or 1 7/8. With a 18 inch extension. A mute point with full exhaust. Either one would suffice
       
    • midnight340

      midnight340 FABO Gold Member FABO Gold Member

      Messages:
      412
      Likes Received:
      245
      Joined:
      Mar 19, 2014
      Location:
      Lawrence, KS
      Local Time:
      8:46 AM
      Thanks guys!!
      I was leaning toward 1-7/8” so this is very reassuring!
       
    • n.y.340 dart

      n.y.340 dart Well-Known Member

      Messages:
      380
      Likes Received:
      277
      Joined:
      Oct 24, 2014
      Location:
      new york
      Local Time:
      8:46 AM
      Ported W2 heads, I run 1 7/8 header.
       
    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

      Messages:
      39,816
      Likes Received:
      11408
      Joined:
      Jun 21, 2005
      Location:
      New York, on a Island
      Local Time:
      9:46 AM
      What heads do you have?????

      Standard port heads for your Street/Strip engine, 1-3/4
      Standard (fully ported) or W2 head for your Strip/Street engine - 1-7/8.

      Note the wording in the bold....
       
    • midnight340

      midnight340 FABO Gold Member FABO Gold Member

      Messages:
      412
      Likes Received:
      245
      Joined:
      Mar 19, 2014
      Location:
      Lawrence, KS
      Local Time:
      8:46 AM
      Fully ported X heads. Bold wording noted. :)
       
    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

      Messages:
      39,816
      Likes Received:
      11408
      Joined:
      Jun 21, 2005
      Location:
      New York, on a Island
      Local Time:
      9:46 AM
      Then I’ll assume this is a bit of a beasty or an engine.
      What’s your cam duration @050?
       
    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

      Messages:
      39,816
      Likes Received:
      11408
      Joined:
      Jun 21, 2005
      Location:
      New York, on a Island
      Local Time:
      9:46 AM
      I like this though on a more conservative engine, I move the pipe size down on on the valve size. This should be a chart for the heavy hitter like street car builds.
       
    • midnight340

      midnight340 FABO Gold Member FABO Gold Member

      Messages:
      412
      Likes Received:
      245
      Joined:
      Mar 19, 2014
      Location:
      Lawrence, KS
      Local Time:
      8:46 AM
      Maybe milder than you are thinking? ... duration at .050" is 235/243, it pulls pretty good 2200 up. Solid with EDM lifters. Fun cam with good pull and a nice sound. I'm only running a 2500 stall from PTC. I do wish I would have had the heads flow tested the last time I had them off.
      Just a feeling, but I think the motor would like to breathe better. I have yet to open the intake for the TQ (adapter for now) and think the headers are too small for what it wants. No way to know without trying it.
       
    • brian6pac

      brian6pac Well-Known Member

      Messages:
      4,919
      Likes Received:
      3348
      Joined:
      Nov 15, 2016
      Location:
      N.E.Ohio
      Local Time:
      9:46 AM
      Put the big headers on it, you will like it.
       
      • Agree Agree x 2
      • Like Like x 1
      • rumblefish360

        rumblefish360 So close, yet so far away FABO Gold Member

        Messages:
        39,816
        Likes Received:
        11408
        Joined:
        Jun 21, 2005
        Location:
        New York, on a Island
        Local Time:
        9:46 AM
        That would be correct. I myself would do a 1-3/4.
        I asked because of the 9.0-1 compression ratio.
        I have a smaller (Hyd. roller) cam in the wife’s 360 @11.6-1 and TF heads W/1.6 rockers. Love the small cam high flow head combo.

        I used to have a LD-340 with the MP mods. Opened up for a TQ and a milled down divider. I ran it with the big TQ. Sold it here a while back. It was very good with the mods and a high lift cam.

        (Note, I’m a nut case that would try everything because I can... for no other reason because I can and don’t mind tinkering with what others call good or perfect.
        Why? .... No, why not! Because I might find something!
        More Power! ROTFLMAO!)
         
        • Like Like x 1
        • smokindust

          smokindust Well-Known Member

          Messages:
          508
          Likes Received:
          49
          Joined:
          Mar 19, 2011
          Location:
          long island
          Local Time:
          9:46 AM
          340s like to rev. Use the 17/8 headers specially if your heads were ported by Mullins!
           
        • midnight340

          midnight340 FABO Gold Member FABO Gold Member

          Messages:
          412
          Likes Received:
          245
          Joined:
          Mar 19, 2014
          Location:
          Lawrence, KS
          Local Time:
          8:46 AM
          Yes, these heads are beautiful. Thanks for one more vote for the 1-7/8”s. I’ve always felt a little guilty about not really using them more fully. The next time they are off I’m getting them to a flow bench to see what they really do.
          Years ago when I first had the seats touched up, the machinist said, “Man, somebody really broke the bank on these heads!!”
          (long story about how I came to have them. ...And this block, which has the cross-over oiling, and other work, done by Larry Atherton’s shop.) Piece of history!
           
        • ir3333

          ir3333 Well-Known Member

          Messages:
          4,808
          Likes Received:
          1345
          Joined:
          Jun 1, 2008
          Location:
          ontario,canada
          Local Time:
          8:46 AM
          1 5/8 circle area = 2.07 sq in
          x 4 = 8.28 sq. in. (One side)
          3 in circle = 7.08 sq. in ( one collector)
          1 5/8 headers already have more volume than the collectors and your still going to
          squash it in to 2 1/2" exhaust pipes on the street.
          ...but if your racing it would be different through open headers, and who knows what
          happens when the exhaust hits atmospheric air pressure after 35 inches?
           
          • Thanks! Thanks! x 1
          • Agree Agree x 1
          • midnight340

            midnight340 FABO Gold Member FABO Gold Member

            Messages:
            412
            Likes Received:
            245
            Joined:
            Mar 19, 2014
            Location:
            Lawrence, KS
            Local Time:
            8:46 AM
            Thanks! I do see that the 1-5/8” flow enough. What always bothered me is the idea that exhaust flow out of a port with equivalent area to 1-7/8” is hitting the smaller header right off the exhaust port. That airflow “dam” off the port has to cause some turbulence that can’t be very helpful to flow.
            When I built/modified these mid-length headers out of a full length set, I did try to radius the transition in the flange a bit, but still... :)
             
          • smokindust

            smokindust Well-Known Member

            Messages:
            508
            Likes Received:
            49
            Joined:
            Mar 19, 2011
            Location:
            long island
            Local Time:
            9:46 AM
            I’ll put my 340s up against any stroker combo any day of the week!
             
            • Like Like x 1
            • rumblefish360

              rumblefish360 So close, yet so far away FABO Gold Member

              Messages:
              39,816
              Likes Received:
              11408
              Joined:
              Jun 21, 2005
              Location:
              New York, on a Island
              Local Time:
              9:46 AM
              I call pit crew member!!!!
               
            • smokindust

              smokindust Well-Known Member

              Messages:
              508
              Likes Received:
              49
              Joined:
              Mar 19, 2011
              Location:
              long island
              Local Time:
              9:46 AM
              Right on!
               
            • B3422w5

              B3422w5 Well-Known Member

              Messages:
              1,360
              Likes Received:
              1346
              Joined:
              Feb 9, 2017
              Location:
              Portage michigan
              Local Time:
              9:46 AM
              1 5/8 should be plenty
               
              • Agree Agree x 2
              1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
                By continuing to use this site, you are consenting to our use of cookies.