Does 0,5" matter? :)

Mopar Exhaust Systems

  1. Wietse

    Wietse Well-Known Member

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    Hey guys,

    Just the good old question about the exhaust system, 2,5" or 3"?
    I have a 440 HP engine in my '69 Coronet R/T, got the TTI headers with 1-7/8" primary's and 3" collector.
    Now to continue this pipe, go 2,5" or 3", as per TTI the 2,5" system is good for up to 475hp.
    Engine is not stock, Hughes camshaft (HE3844BL), 238/244 @ 0.050", .572/.576" lift, Edelbrock performer RPM intake and 770CFM Holley carb.

    My idea is i will not make 475hp with this combo, then again a lot of people say to go with 3".
    I am planning to go with the H-pipe design if it makes a difference.
    Would it make a difference in exhaust note as well?

    Any advise is welcome!
     
  2. hunt2elk

    hunt2elk FBBO Gold Member FBBO Gold Member

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    I would go with 2.5" to at least a 500hp motor. Just put my first 3" TTI system on my Bee and it is very tight by the rear axle and gas tank. The only reason I went to 3 is because this motor is making around 600hp.
     
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    • 451Mopar

      451Mopar Well-Known Member

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      On my '69 Coronet R/T Convertible, I used the same 1-7/8" headers and the 2.5" "X" pipe exhaust, but with stainless Walker Quiet-Flow Mufflers (I don't need a real loud exhaust, and I don't need to go faster as the Convertible is supposed to be required to have a rollbar when running quicker than 14.0, and the car runs in the 13's pretty easy. The Engine is a 4.25" stroked 0.030" over 440 (505") with ported stealth heads, and a hydraulic roller cam about the same duration as your Hughes cam. The "x" pipe exhaust seemed a bit harder to install than the "H" pipe exhaust on the Charger? I think that I like the "H" pipe setup and sound better in my opinion.
       
    • moparedtn

      moparedtn Ed on the Ridge FBBO Gold Member

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      The Engine Masters did a dyno test on this very subject. Their test engine was a big block Chevy that made
      about 620hp with open headers:

      Results? 3" did make a difference. The question for you is: is it worth the little bit of difference to have a
      markedly larger, noisier system under the car? I have 3" duals all the way back on my GTX and it's a pain.
      It's gotten in the way a lot when working on other things, for example.
      Floorboards are going to be warmer with 3", too.
       
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      • Wietse

        Wietse Well-Known Member

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        Thx for the reply guys.
        That video is one of many i've seen saying going bigger is better, but that has more hp then mine does.
        I don't want too much noise either, i love that American V8 rumble but want to be able to have a conversation in the car as well.
        I did pick the H-pipe design as well as i read that it sounds better then the X-pipe...although the X makes a few more horses.
        So a 3" would be louder as the 2,5", i did not know it was that much hassle to get the 3" around the rear axle and fuel tank also.
         
      • BSB67

        BSB67 Well-Known Member

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        Often times folks see this clip and conclude that they need or should get 3" for their 500 hp or less motor. I don't know if its because they just listen to the narrative and don't look at the data or what.
         
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        • dadsbee

          dadsbee FBBO Gold Member FBBO Gold Member

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          Sometimes a little back pressure is a good thing!! :thumbsup:
           
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          • Wietse

            Wietse Well-Known Member

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            As stated in my other post, i did (as others) pay attention on the numbers given in that video.
            There is more opinions around than only that video where people still recommend to go 3" despite the fact they do not reach the magic 475hp figure.
            I am just seeking advise from people who can say "been there, done that" and if there would be any reason for picking a 3" over the 2,5" for my particular (or similar) setup.
             
          • Don Frelier

            Don Frelier FBBO Gold Member FBBO Gold Member

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            Note they didn't have an H-pipe during the test.
             
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            • moparedtn

              moparedtn Ed on the Ridge FBBO Gold Member

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              Well, I can tell ya that for my little old 450hp 440 in my GTX, 2 1/2 would have been just fine.
              The factory deemed it fine to go with factory manifolds and 2 1/2 headpipes/ 2 1/4 tailpipes for a 375hp 440, after all.
               
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              • Wietse

                Wietse Well-Known Member

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                TTI themselves state there is a difference between the H and X system.

                Quoted from their website:
                H-pipe systems have proven to provide increased horsepower over the stock straight-pipe systems whereas the X-pipe systems have proven 12-15 more horsepower gain at the rear wheels over the H-pipe.
                 
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                • Wietse

                  Wietse Well-Known Member

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                  Yes, but now change the stock restrictive manifold to a better flowing header and a camshaft that pushes a bit more air as well i guess a full 2,5" exhaust will compliment that right?
                   
                • moparedtn

                  moparedtn Ed on the Ridge FBBO Gold Member

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                  ….and different mufflers will make a difference.....and oval versus round piping matters....and....and....
                  As Steve says in that video, the entire package - from air cleaner to exhaust tips - matters.
                  One has to determine their priorities, from cost, to ease of installation/maintenance, to expected service life,
                  to clearance underneath to perform other work, to desired sound....and on and on.

                  All I can do is refer you to some concrete evidence (the video) just like others are offering referral to other
                  sources of data (like TTI), along with my own experiences.
                  If it's me and I'm insisting on running headers (and I am now on my GTX), I'd run a 2 1/2" dual system with an
                  h-pipe crossover that has an easily-disconnected cross pipe for serviceability of transmission, etc.
                  I'd run two chamber mufflers, not fiberglass-stuffed but actual chambers, some manner of Flowmaster 50 series
                  or clone.
                  That's just my own two cents.
                   
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                  • khryslerkid

                    khryslerkid FBBO Gold Member FBBO Gold Member

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                    2 1/2"
                     
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                    • 33 IMP

                      33 IMP Well-Known Member

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                      It sounds like you answered your own question. Not enough power to need 3", and you want a reasonable noise level. H-pipe 2 1/2 sounds like what you want . Muffler selection is important to get the sound you want though too.
                      I agree with moparedtn, I love my 50 series flowmasters, but man, they went up in price since I bought mine!
                       
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                      • Stanton

                        Stanton Well-Known Member

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                        Run 3" to a cutout then 2-1/2 from the cutout back. You'll have the best of both worlds when the need arises.
                         
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                        • Wietse

                          Wietse Well-Known Member

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                          As per the TTI website the exhaust comes with Dynomax super turbo mufflers which have 2 chambers, although filled with fiber glass.
                          https://www.dynomax.com/mufflers/super-turbo-mufflers

                          If i don't like it i guess i can always change the mufflers with something else as the 50 series flowmasters as you guys recommend. (i believe the 40 series are very loud right?)

                          I kind of made up my mind before to go with 2,5", but before putting the order in i wanted to see if there is any other comments or suggestions of picking between the 2 different sizes.
                          That the engine does not require it is 1 thing, but if the exhaust tone would improve a lot that could have been a reason for going 3".
                          But if the 3" is more loud, more clearance issues and the fact i don't need to run it i am confident of getting the 2,5" setup.

                          Running a cutout with bypass would be something fun as well, although i always wonder how long these bypass valves live in those surcumstances before getting seized or so?

                          Thx for the tips and tricks from you all!
                           
                        • moparedtn

                          moparedtn Ed on the Ridge FBBO Gold Member

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                          Louder than the 50 series, yes. Considerably so, not to mention drone is an issue with them when cruising
                          down the highway.

                          Exactly. Although it's only a half inch in name, 3" pipes are CONSIDERABLY larger than the 2 1/2 and if the only
                          time the 3" is a little better is when you're at full throttle at high RPM, to me it isn't worth dealing with the rest
                          of the time - especially when working on the car and especially with the heat generated in the cabin.

                          Good luck!
                           
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                          • BSB67

                            BSB67 Well-Known Member

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                            There are folk making over 800 hp, and running in the low 10's at 133 mph with 2.5" exhaust. It's class driven so they have to, otherwise they wouldn't, and would make more power and go faster with something bigger. But I simply express it now to put some perspective on the exhaust size discussion.

                            I've run in the 12s at 108 mph with a 2 1/4 compression bent system in a 4200 lb car with a stock ish 440 and 3.23 gears and the Dynomax super turbo 17747 mufflers. Do you have any idea what 2 1/4" compression bent tail pipes look like. It's ugly.

                            Run what you want. And it would be silly to run too small of an exhaust system if max power is you're only top priority. But balance your decision making with logic and real evidence.
                             
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                            • 33 IMP

                              33 IMP Well-Known Member

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                              Be aware, the 50 series big block flowmaster are huge, at least mine are. 5x12x22" case, 28 overall .
                               
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