necking down after collecter?

Mopar Exhaust Systems

  1. 70DusterBob

    70DusterBob Well-Known Member

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    The shop my Duster is in wants to neck down the exhaust from TCI headers to a 2 inch pipe. The collectors are 3", after the foot of 2" pipe they plan to use, the 2" extensions the headers came with, they plan on going to 3" out the back. Is this stupid or a good idea?

    Thanks
     
  2. MOPAROFFICIAL

    MOPAROFFICIAL Well-Known Member

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    What cid and cam duration?
    I can about guarantee it's a stupid idea.
     
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    • Treblig

      Treblig Well-Known Member

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      One muffler shop dude told me (and it made sense) that the exhaust is hot near the headers and cools as it travels out the back. That's why you can hold your hand over the rear exhaust pipe but not at the header outlet (too hot). Cooling gas should condense.....so the same amount of exhaust gas (volume) at the header should decrease in volume by the amount that it cools (temp) off as it travels to the rear.
       
    • 70DusterBob

      70DusterBob Well-Known Member

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      It is a BPE 408 with the following specs:

      · HP & Torque: 445 HP / 500 FT LBS
      Compression Ratio: 10.1:1
      Aluminum Heads
      Flat Tappet Cam
      Cast Steel Crank
      Forged Pistons

      Block:

      · Hand picked seasoned block
      Square and parallel decked
      Align honed main bearing bore
      Cylinders honed on computer controlled machine to within .0002 straightness and roundness
      Cylinders are sonic tested for thickness
      2-Bolt Main
      4.000" Bored .040" over
      2-Piece Rear Main Seal
      Mech fuel pump provision: Yes

      Rotating Assembly:

      · New Cast steel crankshaft
      4.000" Stroke
      OEM type 6.123" connecting rods w/ 150,000 psi bolts
      Forged pistons
      External

      Cylinder Heads:

      · Aluminum Cylinder Heads - 63cc chamber
      2.02" intake/1.60" exhaust valves
      171cc intake/77cc exhaust runners

      Cam Specs:

      · Cam Type: Flat Tappet
      .545 Intake .545 Exhaust
      241 Intake / 247 Exhaust duration
      @ .050 - 110 degree lobe separation

      Ignition Timing:

      · 34 degrees total at 2500-3000 RPM
       
    • RustyRatRod

      RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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      Dumbest crap I ever read. 3" all the way.
       
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      • MOPAROFFICIAL

        MOPAROFFICIAL Well-Known Member

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        You're referring to what's called "tuned exhaust".... what you do.. is... you take shoe polish, and you wipe a fkn line every 8 inches from the collector on the extension.... or about 3 line...the last line of shoe polish that burns off.... is where you would attach the muffler....imo that has NOTHING to do with the diameter required...smaller would probably move that line further down the pipe even..'more heat'. Need to know what you're doing and not let some Ck biter steer you queer.
         
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        • 70DusterBob

          70DusterBob Well-Known Member

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          He was mentioning something like that, that the neck down needed to be where the paint no longer burned off the exhaust was his explanation. You did a much better job of it. I'm just concerned that it is not far enough back and too narrow. I posted the specs above for the engine. I have 3 step headers on it: 1-5/8 to 1-3/4 to 1-7/8 into a 3" collector.
           
        • Phreakish

          Phreakish Well-Known Member

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          Do you really mean they want to go straight to 2" and then later bump it back to 3"??

          Stupid.

          Except for maybe using a choke at or in the collector, the exhaust should continue at collector diameter for some length and terminate into very large volume in order to take advantage of any wave tuning the extension might help create.

          This is a good article.
           
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          • MOPAROFFICIAL

            MOPAROFFICIAL Well-Known Member

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            Re cam that pos too.
            The heads on it, should make 500
             
          • Scamp Rohnda

            Scamp Rohnda Well-Known Member

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            Check with Johnny Mac and Blue Point, I'll bet they have your answer.
             
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            • rumblefish360

              rumblefish360 So close, yet so far away FABO Gold Member

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              Quick! Run away, very quickly. Run your ass off. There secretly anti MoPar as well as plain old fashion stupid.
               
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              • 70DusterBob

                70DusterBob Well-Known Member

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                Sounded like crap to me too. I'm looking for 3" extension/collectors, Summit does not have a 3" in 3" out. Not that I can find.
                 
              • 70DusterBob

                70DusterBob Well-Known Member

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                LOL, I hear ya.
                 
              • 70DusterBob

                70DusterBob Well-Known Member

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                Gotcha
                 
              • rumblefish360

                rumblefish360 So close, yet so far away FABO Gold Member

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                Favorite post and best next move after you run Away from that asshole lead exhaust shop that contains morons and asshats inside out being worn upside down.
                Smartest post yet. Possibly better yet, get the book by David Vizard.
                 
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                • thesiren74

                  thesiren74 Well-Known Member

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                  2 1/2" minimum, 2" is for a stock 318
                   
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                  • rumblefish360

                    rumblefish360 So close, yet so far away FABO Gold Member

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                    Go to Jegs
                     
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                    • Phreakish

                      Phreakish Well-Known Member

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                      Like this?

                      You can also get 3" "reducers" made for a 3" collector that are made to weld the rest of your exhaust to. Either way works. The torsion bar cross member is typically pretty close though... So the longer extensions may be more trouble.
                       
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                      • rumblefish360

                        rumblefish360 So close, yet so far away FABO Gold Member

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                        I don’t even think the stock 318 ever cam with a 2 inch exhaust. IIRC (LMAO @ that but....) stock exhaust tubing is 1-7/8. Correct?
                         
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                        • Phreakish

                          Phreakish Well-Known Member

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                        • thesiren74

                          thesiren74 Well-Known Member

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                          It was an example.
                           
                        • rumblefish360

                          rumblefish360 So close, yet so far away FABO Gold Member

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                          Gotcha!!!
                           
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                          • Treblig

                            Treblig Well-Known Member

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                            • 70DusterBob

                              70DusterBob Well-Known Member

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                              • 70DusterBob

                                70DusterBob Well-Known Member

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                                They are TCI headers if I remember correctly. The pipes going into the collector are huge, 2" is barely half the size. I'm like?????
                                 
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