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I mic’d mine too 2.55 ID 2.78 OD . 3 inch to 2.5 reducer is what it takes to mate 6.4 mid pipes to the exhaust on 17 up 5.7 cars .
 

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2015 RT 5.7 M6
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That does not make sense, I just installed and 3" AWE 6.4 catback and at the h-pipe to mid pipe joint the i.d. is 2.75" and it is designed that way so it can mate up to a 6.4 stock mid pipe which should then have a 2.75" O.D. If it was 3" then I would not have had to run a 3" to 2.75" reducer as my header mid pipes are 3".


My 2015 stock mid pipe OD measures 2.446".

But in all fairness you measured OE parts so I have to believe what you say but it does not jive with what I have seen with the aftermarket catback systems.
 

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Here is another data point from and email from AWE when I asked about the difference between the 6.4 and 5.7 exhaust systems they sold.

"Since you have a 2.75-3" adapter, I suggest getting a SKU for a 392 so you get an H with a 2.75 inlet instead of the 2.5 found on the 5.7L.

The drone-canceling 180 Technology is in the rear cans, not the center resonators. We just recommend going resonated with LTHs as it keeps some of the visceral aggression toned down."
 

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2015 RT 5.7 M6
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I mated 2.75 id h-pipe side (female) to 2.75 od (male) from the reducer (3 inch ID to 2.75 in OD). See pic in this post.

This weekend I plan on working on the exhaust, I will take exact measurements of my setup. Why...because I was pulled over for speeding (officer was really cool and just said slow it down but he did say I need to tone down the exhaust.). Going to install some 3" thru mufflers...looking at vibrant and 3" pype butt connection clamps.

How do you mate 2.75 to 2.75 ? unless you’re welding it there’s no male into female connection.
BTW you can without welding as Pypes makes clamps like these (they connection is airtight...used them on my corsa when I replaced mid mufflers with straight pipe)...although only in 2.5 and 3 inch sizes.
 

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BTW you can without welding as Pypes makes clamps like these (they connection is airtight...used them on my corsa when I replaced mid mufflers with straight pipe)...although only in 2.5 and 3 inch sizes.
Those clamps actually work, my clamp on O2 bung uses one similar and it surprised me how well it worked
 

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2015 RT 5.7 M6
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Those clamps actually work, my clamp on O2 bung uses one similar and it surprised me how well it worked
Yeah they do, they work way better than the stock slip-on and clamp connections. Was the only connection that did not drip water and no signs of exhaust leakage when I took them off. They are pricey but worth it.
 

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Discussion Starter #28
2.75 OD . 2.5 ID .. mic it ..I did when I installed the 6.4 manifolds and mids from my Scat on my 18 R/T. 3 inch to 2.5 inch reducer is what I needed to mate with the 5.7 exhaust.
I have a 19 RT but I’m still confused on what I need for the install. Will I need the mid pipes with cats or will I need some other part for it?

Yes 2.75" but I believe the connection between mid-pipe and x-pipe is 2.5".
I’m not very well informed on cars but are you saying here that I need a reducer from srt mid pipes to my car back here
 

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What I am saying is that SRT mid pipes will not fit the RT x-pipe so there will be some modification required. Why do I believe, because AWE used a 2019 RT to design and build their catback system and they stated the difference between the 5.7 and 6.4 systems is the connection at the mid pipe to cat back.
 

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Discussion Starter #30
What I am saying is that SRT mid pipes will not fit the RT x-pipe so there will be some modification required. Why do I believe, because AWE used a 2019 RT to design and build their catback system and they stated the difference between the 5.7 and 6.4 systems is the connection at the mid pipe to cat back.
So going off with that info what size reducer will I need to fit the mid to x pipe and where can I find the mid pipes with cats in them?
 

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I think you will need a 2.75" I.D. to a 2.5" I.D. You will also need to cut the mid pipes to accomodate the reducers (don't forget clamps).

To know for sure, get some calipers and measure the O.D. of the 5.7 mid-pipe. For example, on my 2015 the mid pipe has a ~2.5" O.D.

As to where you can buy the mid pipe (cats are welded onto them already) check ebay or you can buy new (~$1k ea):

68281724AA - Right mid pipe for 6.2
68281725AA - Left mid pipe for 6.2

Some places like rockauto charge a core charge.
 

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2018 Scat Pack Charger 11.995 first time out stock tune
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Check for sale section for Rt upgrade. 2018 6.4 shorties and catted mid pipes 48k miles... ;)
 

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Did not catch that sorry. I fumble here and there.

Give me a few and I will measure 2018 6.4 OD catted mid pipe size at cat back.

They are in fact at the opening a hair under 2.75 inches. Now they bevel down at the opening... Down to that. The pipe then expands out a little bigger. I know that a tailpipe expander is needed when adding Jba cattless to the stock scat cat back to open it up to get the pipe to insert.

My 2 cents for the day.
 
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