3 inch exhaust

Mopar Exhaust Systems

  1. steve340

    steve340 Well-Known Member

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    Magnaflow have some good tech info on pipe size for single or dual pipes if anyone is interested.
    My rule of thumb is on a street car go smaller or be conservative with exhaust pipe size.
    And if you can be bothered - never met an engine that didn't like headers.
     
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    • Beep!Beep!

      Beep!Beep! FBBO Gold Member FBBO Gold Member

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      yes good info and road kill did a test on 2.5 versus 3 on a big block chevy and same length and same magma flow mufflers and the 3 inch added 20to 30hp maybe bull but it was on a dyno ?
       
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      • steve340

        steve340 Well-Known Member

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        It was no doubt correct the 3 inch pipe may well net a horsepower increase but it will almost certainly be in the upper RPM range. In those tests they will perhaps not mention the torque figures. Most dyno runs will only show you what is happening from 3000 or higher.
        A true street engine has to have torque available from low rpm but a race motor may not - or the owner may be OK with a peaky or temperamental street engine.
        3 inch pipes would be needed for some very wild or large capacity street engines.
        I have a 363 engine with 3 inch pipes - it pulls like a train from 3000rpm but the car is a manual transmission and the car is very light. It would be pretty hopeless on the commute to work.
         
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        • hunt2elk

          hunt2elk FBBO Gold Member FBBO Gold Member

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          I got talked into using 3" exhaust on my 493 stroker by TTI because the motor is around 580hp. I absolutely hate the sound and wish I would have went 2.5" like what's on my other cars. Doubt I will ever see an advantage as I don't race the car.
           
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          • Ron H

            Ron H FBBO Gold Member FBBO Gold Member

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            This discussion got me thinking more about my poly build getting talked into 3" with an X arrangement and headers. It has flow masters and it sounds mean; but too loud for my preference cruising. The low end giddy-up to me is pretty wimpy considering all the work done on the build. The only difference I can note is better top-end. Been going on 3 years now since the re-do and maybe 3000 miles. Something never seemed 'compatible' to me - a miss match and maybe part of this just could be the pipes. Maybe if I put on more restrictive mufflers to quell the noise, this could be a plus...
             
          • toolmanmike

            toolmanmike Moderator Staff Member FBBO Gold Member

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            No
             
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            • Skytrooper

              Skytrooper FBBO Gold Member FBBO Gold Member

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              I went with a 3" system based upon my header outlet size being 3". I am having difficulty fitting it around thr rearend and gas tank. I am really thinking of just buying a smaller diameter system.
               
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              • moparedtn

                moparedtn Ed on the Ridge FBBO Gold Member

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                Fred came to me with Hedmans and a full 3" dual exhaust - and I wish he hadn't.
                Previous owner had it all custom bent because he liked the sound with Flowmaster copycats.
                Me? It's TOO FREAKING LOUD and that's saying something, because I like my Mopars to talk a little.
                Big-arsed pipes get in the way when you're under there working on stuff and you got to get them
                adjusted juuuust right or they rattle on this or that under there, too....
                Problem is, I won't just yank it all off there as long as it doesn't rot out and it's all heavy stainless.
                Dammit. :)
                 
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                • 440 4 speed

                  440 4 speed Well-Known Member

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                  3 inch pipes fit extremely tight on 66-7 b bodies, a pain to install doing it on jack stands.
                   
                • Don Frelier

                  Don Frelier FBBO Gold Member FBBO Gold Member

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                  You could just put the mufflers on for now.
                  Bring everything over when the weather is better.
                  David can cut, weld and fit it in if it's at all possible.
                  If he can't get it to fit then you can just reduce at the muffler outlet and use the original 2-1/4" tailpipe from Accurate I think that is what the original size would be.
                   
                • Ron H

                  Ron H FBBO Gold Member FBBO Gold Member

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                  Well if I had a do-over I'd dump the 3"...too much cash to re-do now. I also have flow masters that are too loud plus the 3" setup is too big for my motor. Plan is to install quieter mufflers and fit it to 2.5" in and out and be done with it.
                   
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                  • Don Frelier

                    Don Frelier FBBO Gold Member FBBO Gold Member

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                    The slotted tips are pretty awesome.
                    If you can install the mufflers with a band clamp.
                    They likely will need to come off at some point.
                     
                    Last edited: Feb 23, 2021 at 3:12 PM
                  • toolmanmike

                    toolmanmike Moderator Staff Member FBBO Gold Member

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                    6" total is what the diesel trucks run. :lol:
                     
                  • MiradaMegaCab

                    MiradaMegaCab Well-Known Member

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                    94A0A0E1-7A0D-425B-A78B-2625DE98DF05.jpeg
                    Fab your own.
                     
                  • 69a100

                    69a100 Well-Known Member

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                    This is a true case where bigger isn't always better! Good Luck
                     
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                    • 6PKRTSE

                      6PKRTSE Well-Known Member

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                      Yep, I have done several sets of 2-1/2", 3" and 3-1/2" exhaust systems on my own with nothing more than some jack stands, Miller 110 welder, mandrel bends and straight pipe pieces, bench vise and hand held band saw.
                       
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                      • That_Tall_Dude

                        That_Tall_Dude FBBO Gold Member FBBO Gold Member

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                        3” will be louder...

                        If your trying to maximize peak hp, then 3” probably makes sense.

                        But since you’re doing manifolds it looks like you favor practicality (balancing performance, quiet, maintenance, access, etc), then 2.5” is probably the way to go

                        Most stuff seems to say 3” for over 450 hp...

                        if you wanna geek out on back pressure & velocity this one is fun

                         
                      • 33 IMP

                        33 IMP Well-Known Member

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                        A three inch system will not automatically be louder. It depends on muffler selection. I guarantee that a three inch in/out in a triple pass case 24" long will be quieter than a 2 1/2 "fourteen inch long case straight through. If you want it quiet, buy a quiet muffler.
                         
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                        • That_Tall_Dude

                          That_Tall_Dude FBBO Gold Member FBBO Gold Member

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                          true, but the same muffler (2.5” vs 3”) in a 3” will be louder than a 2.5” right
                           
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                          • That_Tall_Dude

                            That_Tall_Dude FBBO Gold Member FBBO Gold Member

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                            What don’t you like about the sound? Just wondering...
                             
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