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Discussion Starter #1 (Edited)
Does any one have 3 inch exhaust piping instead of the stock 2.5 exhaust piping? Just a little curious, my friend told me about his other friend who had an r/t with 3 inch all the way back and it was awesomely loud... but then I thought to my self... hmm that probably made the car slow and sluggish because of exhaust scavenging.. and yea :)
 

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I installed SRT headers and full 3" Dynomax catback on a 10 model RT. Just about pointless. The 2.5 is more than efficient for a stock Hemi.
 

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I've got a Magnaflow 3" cat-back. It's fairly loud, but I feel like that's due to the mufflers, not the pipe size.
 

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Discussion Starter #4
I've got a Magnaflow 3" cat-back. It's fairly loud, but I feel like that's due to the mufflers, not the pipe size.
ok thank you! I am actually going to keep the stock 2.5' . gunna go with long tube headers and catless mids with complete straight pipe . little backpressure with free flowing, high velocity exhaust scavenging should get me the most power.. I feel if I did 3' the exhaust scavenging with me recirculating way to slow since the pipe is so big.
 

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Does any one have 3 inch exhaust piping instead of the stock 2.5 exhaust piping? Just a little curious, my friend told me about his other friend who had an r/t with 3 inch all the way back and it was awesomely loud... but then I thought to my self... hmm that probably made the car slow and sluggish because of exhaust scavenging.. and yea :)
Dodge can call it 2.5" if they want too just like advertising the wheels as 20"x 9" when they are 20x8's as stamped on the rim. I just cut the resonators out from under the rear two weeks ago and installed some true 2.5" 304 stainless turbo pipe I had and it SWALLOWED the stock exhaust pipe. The 304 pipe is a true 2.5" OD pipe and is .065 wall. Twice as thick as the stock pipe and still had close to an 1/8" gap all the way around the joint where I welded it. I also noticed that the stock pipe necks down severely at the mufflers (2" maybe) where the weld is in and out of the stock mufflers under the car. I used about 28" on each side of the 2.5" stainless and the car has a very nice rumble now when at part throttle and up, but not very much drone at all at highway speed or in MDS.
 

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Discussion Starter #6
Dodge can call it 2.5" if they want too just like advertising the wheels as 20"x 9" when they are 20x8's as stamped on the rim. I just cut the resonators out from under the rear two weeks ago and installed some true 2.5" 304 stainless turbo pipe I had and it SWALLOWED the stock exhaust pipe. The 304 pipe is a true 2.5" OD pipe and is .065 wall. Twice as thick as the stock pipe and still had close to an 1/8" gap all the way around the joint where I welded it. I also noticed that the stock pipe necks down severely at the mufflers (2" maybe) where the weld is in and out of the stock mufflers under the car. I used about 28" on each side of the 2.5" stainless and the car has a very nice rumble now when at part throttle and up, but not very much drone at all at highway speed or in MDS.
hmm, very interesting information man, thank you! are you running a straight pipe?
 

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I just got Solo Performance catbacks installed on my 392. They are 3 inches through and through, and the craftsmanship is impressive.

They bolted on relatively easily, and they are LOUD, but I think primarily because it only has a smaller muffler in the middle and that's it. I believe you can mount the same on an R/T.

My car already had the Mopar CAI, and now that I added those catbacks, the engine feels so much more responsive than stock!
 

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Discussion Starter #8
I just got Solo Performance catbacks installed on my 392. They are 3 inches through and through, and the craftsmanship is impressive.

They bolted on relatively easily, and they are LOUD, but I think primarily because it only has a smaller muffler in the middle and that's it. I believe you can mount the same on an R/T.

My car already had the Mopar CAI, and now that I added those catbacks, the engine feels so much more responsive than stock!
ahh very cool man, thank you for the response! I am planning to keep stock pipes but have long tube headers and straight pipes after (catted midpipe) then dyno and custom tune.. what do you think about this setup?
 

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3" Flowmaster Super 44's
 

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There is no audible difference in exhaust note between 2.5" dia exhaust pipe versus 3" dia., all other aspects of the exhaust system being equal.
 

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The automatic challenger RTs come with 2.5" pipe out of the cats but then step down to 2.25" right before the x-pipe. The manual challenger RTs come with 2.5" all the way out the back. I had a 2009 that was auto and had the step down in exhaust size. It might have changed since then though.


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Discussion Starter #12
The automatic challenger RTs come with 2.5" pipe out of the cats but then step down to 2.25" right before the x-pipe. The manual challenger RTs come with 2.5" all the way out the back. I had a 2009 that was auto and had the step down in exhaust size. It might have changed since then though.


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I just wonder stepping up to 3 inch after the HF cats will cost me loss in performance??
 

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You want to maintain as much exhaust velocity (modest pipe size) as possible w/o suffering undo drag (pipe too small for the application). Exhaust velocity helps engine output, while drag (from too much velocity) diminishes engine output. That's why playing around with 3" pipe is a dangerous game (if you are concerned about across the board engine performance), unless you plan to up the displacement, up the redline (and spend a lot of time up there), or go to forced-induction.

Since you already have a cross-over pipe (hopefully a functional one) on this car, that will give you extra headroom as well to guard against any sort of pipe too small phenomenon. Basically, you got 2 full-size exhaust pipes to equalize any high-flow event that occurs upstream on either pipe (toward the catalyst) at any given moment. Long story, short...don't worry about it. Dodge already hooked you up with a trick system. ;)

The real source of the bottleneck that you should address before tweaking the pipe size is always the muffler. Worry about the muffler, not the pipe. You can up-size the muffler to minimize any restriction penalty, and there is no penalty on engine performance if you go overboard, since it is the velocity in the pipes that is the critical factor in the exhaust tuning. If it is a baffle/chamber style design, go with least number of chambers and up-size. If it is louvered-glass pack, go with a short cylinder and up-size (inlet/outlet/internal core). If it is a perf-core, straight-thru design...sit back and relax...that's as optimal a design as you can get for minimal muffler restriction. :D

If you are really sold on the 3" pipe look (especially at the tailpipe), then you should just use the oversize pipe in the last foot or so of the exhaust system. That will also give you the commensurate loudness effect of a larger radiating window.
 
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I put my 2012 srt exhaust on my 14 shaker,it does give it a little deeper sound at idle,and a little louder driving
 

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Discussion Starter #15
You want to maintain as much exhaust velocity (modest pipe size) as possible w/o suffering undo drag (pipe too small for the application). Exhaust velocity helps engine output, while drag (from too much velocity) diminishes engine output. That's why playing around with 3" pipe is a dangerous game (if you are concerned about across the board engine performance), unless you plan to up the displacement, up the redline (and spend a lot of time up there), or go to forced-induction.

Since you already have a cross-over pipe (hopefully a functional one) on this car, that will give you extra headroom as well to guard against any sort of pipe too small phenomenon. Basically, you got 2 full-size exhaust pipes to equalize any high-flow event that occurs upstream on either pipe (toward the catalyst) at any given moment. Long story, short...don't worry about it. Dodge already hooked you up with a trick system. ;)

The real source of the bottleneck that you should address before tweaking the pipe size is always the muffler. Worry about the muffler, not the pipe. You can up-size the muffler to minimize any restriction penalty, and there is no penalty on engine performance if you go overboard, since it is the velocity in the pipes that is the critical factor in the exhaust tuning. If it is a baffle/chamber style design, go with least number of chambers and up-size. If it is louvered-glass pack, go with a short cylinder and up-size (inlet/outlet/internal core). If it is a perf-core, straight-thru design...sit back and relax...that's as optimal a design as you can get for minimal muffler restriction. :D

If you are really sold on the 3" pipe look (especially at the tailpipe), then you should just use the oversize pipe in the last foot or so of the exhaust system. That will also give you the commensurate loudness effect of a larger radiating window.
you sir, are absolutely amazing :) thank you for the great post, learned a lot!
 

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Where are the dyno numbers to back up these statements? I just can't believe that you would lose any power with a 3" exhaust on a 5.7L Hemi. I had a Z28 Camaro with a 5.7L that made less power, and they were proven again and again to benefit more from 3" exhaust than 2.5" or 2.75" exhausts.

randycat99 stated the correct rule, that it is about maximizing exhaust velocity. That doesn't mean that a 3" exhaust will have less velocity than a 2.5" exhaust, and saying that Dodge must have given us the best exhaust possible from the factory is just plain wrong. It may be better or worse, but you would need real world testing with numbers to back it up, not just opinions.
 

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Yes, for volumetric flow x, 3" pipe will translate to less velocity than in a 2.5" pipe. That part is just pure mathematics and cross-sectional area.

Whether more velocity or less velocity would be beneficial for a particular engine at a particular rpm, that is the big unknown factor, of course. Too little velocity and the engine tuning effect suffers, while too much velocity and drag losses begin to rob engine output. Somewhere in the middle is the sweetspot. ;)

Now if you got sharp bends in your pipe, that adds another element of complexity to the notion of pipe size. The bend may act as a smaller cross-section than it physically is. The bottleneck to velocity is at those points. So if you have a lot of them, maybe you are better off with a larger pipe...not because there was any problem with the native pipe size, but to compensate for the bended areas of the pipe.
 
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Discussion Starter #18
Well, now I'm just stuck and back where I started :/ I don't have the funds to put on dyno now, then add 3 inch, then dyno again, then if not a performance increase put back the 2.5.....

I just really wanted my car to sound louder lol.....
 

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According to MBRP their 3 inch cat back exhaust for the 5.7 actually gives 10% more hp at lower rpm than stock. They claim that the secret to this power increase at lower rpm with 3 inch pipes is possible due the 2.5 inch exit at the tip. Lisa from Speedlogix also saw all around hp gains on her dyno with MBRP on her otherwise stock R/T.
 

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Well, now I'm just stuck and back where I started :/ I don't have the funds to put on dyno now, then add 3 inch, then dyno again, then if not a performance increase put back the 2.5.....

I just really wanted my car to sound louder lol.....

It'll certainly be louder... :p
 
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