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Discussion Starter #1
Hello and thank you for attempting to read my poorly constructed thoughts. This thread is about LT's and a catback that matches up well.

I have very recently talked with Tim Barth over at MPH about headers for my '12 R/T. He was very sure I should be using 1 3/4 primaries rather than the 1 7/8 ones because of the 345. I made sure he to tell him I have a supercharger on it and he said you STILL will be much better off using the 1 3/4.

^^^^ I am going to use 1 3/4 but I just wanted everyone to know why I chose that size.

The thread is about which brand bolts in well and has a good marriage with the catback system.


So my first impulse is to go with the STP 1 3/4 LT's and also buy the catback system that was designed to go with the headers..... that would be the LM1.

Another thing I noticed was that ARH and borla also make 1 3/4 primaries but I want a catback that will bolt up without ANY modification. I am doing this project in my garage mind you.

Please share some thoughts with me guys. I have been working a ton of OT so I have the money but I won't spend it until I feel confident in my decision.
 

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Kooks LT and mids
 
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Discussion Starter #3
Thanks ghost.

I c you have kooks on. Did the catback system you chose bolt right up easily?
 

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ARH and catted mids into Borla ATAX, have not installed yet but plenty have, NP. Agree that 1-7/8" tubes are too big also, so no Kooks as theirs are all 1-7/8".
 

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Thanks for this thread, I am in the same boat with a solo catback system and I am shopping for lt's. I was leaning to the Kooks , as I have nothing but great things about them from many hemi shops that post here.

So why not the 1 7/8" tubes for a 345?
 

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Thanks for this thread, I am in the same boat with a solo catback system and I am shopping for lt's. I was leaning to the Kooks , as I have nothing but great things about them from many hemi shops that post here.

So why not the 1 7/8" tubes for a 345?
The easy answer is that in some of our opinions, including Bart in the OP the 1-3/4 flow better as long tubes is all and larger is not better in our opinions, so kind of limits you to who actually builds em to that spec.
 

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Discussion Starter #7
Thanks for this thread, I am in the same boat with a solo catback system and I am shopping for lt's. I was leaning to the Kooks , as I have nothing but great things about them from many hemi shops that post here.

So why not the 1 7/8" tubes for a 345?
NP.

About sizing the primaries... To be completely honest I researched a little and I decided I would just call Tim Barth. He is one of the most well respected tuners in the country. He told me I would be happiest with the 1 3/4. On a 5.7 this makes the most power over the entire powerband... 1 7/8 may make more power @ like 6000-6200 rpm, but would be lower at all other rpm.

I think the 3.6L= 1 5/8, 5.7L= 1 3/4, 6.4= 1 7/8... after that you get into goofy things like stepped headers with 4" collectors, more custom stuff.
 

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Discussion Starter #8
Thanks Bee, I'm glad to know about that option.
 

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I bought ARH and installed them myself. They went on perfectly and when I went to connect them to the catback, they would not go in. The catback is a magnaflow competition series. The 2.5 od on the magnaflow pipe actually was 2 5/8. So I just got some 304 2.5 od pipe and connected them. Not a big problem, just unexpected. Still love the headers. :icon7:
 

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Discussion Starter #10
I bought ARH and installed them myself. They went on perfectly and when I went to connect them to the catback, they would not go in. The catback is a magnaflow competition series. The 2.5 od on the magnaflow pipe actually was 2 5/8. So I just got some 304 2.5 od pipe and connected them. Not a big problem, just unexpected. Still love the headers. :icon7:
Thanks.

Things like this make me want to stick with parts that were made for each other. Sure not a big deal but I want to wrap it up in one weekend.
 

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I did Kooks LT and kooks Hi Flos but I got the SRT Hi Flos ... the 5.7 hi flos neck down to 2 1/2 so you can use the factory cat back ... using the SRT Hi Flos they don't neck down they stay 3" and then put on the SRT Cat back from MBRP and loooove it
 
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^^ That is a sweet sounding combo, just too much for 5.7L IMO and others, and if we dropped the headers free at the connection to mid pipes I would probably wax you, after that joint not much matters, it's the headers primaries that make the difference, too big is farther back doesn't matter as much, and yes they neck down from the 3" at mid pipe to catback, but then again so does stock SRT mid-pipe well past the 2.75" almost 2.5" ID at catback.
 

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Kooks will make a 1 3/4 if you call them.

ARH LT's bolted up to my Zoomers/SX catback.
 

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^^ That is a sweet sounding combo, just too much for 5.7L IMO and others, and if we dropped the headers free at the connection to mid pipes I would probably wax you, after that joint not much matters, it's the headers primaries that make the difference, too big is farther back doesn't matter as much, and yes they neck down from the 3" at mid pipe to catback, but then again so does stock SRT mid-pipe well past the 2.75" almost 2.5" ID at catback.
I would agree that it sounds like to much but it took the car from a 13.9 @ 100 to a 13.3 @ 105 so to say its to much .... on paper maybe .... at the track ... nope seems just rite headers hi flos cat back and a custom tune by Johan got me 370 HP and 406 TQ at AMP in Pompano in just a lil 5.7 with bolt ons is pretty good IMO and I now have 392's in an A5 and the car flyyyys
 

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I now have 392's in an A5 and the car flyyyys
Have you run the 1/4 with the new 392 gear? If so, what were the before and after results?
 

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well it gos like this ..... in cool air .... not cold just cool ... like 62 degrees I ran 13.3 @105 .... in the heat I run consistent 13.6 @ 104 ... now with the gears in the heat I ran back to back 2 runs @ 13.2 @104 and I have not gone in the cool weather ... so if I could pick up the same 3/10 in the cool should run a 12.9 ... but that's just if the numbers work out like that .... as soon as I run in cool weather I will post up
 
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I would agree that it sounds like to much but it took the car from a 13.9 @ 100 to a 13.3 @ 105 so to say its to much .... on paper maybe .... at the track ... nope seems just rite headers hi flos cat back and a custom tune by Johan got me 370 HP and 406 TQ at AMP in Pompano in just a lil 5.7 with bolt ons is pretty good IMO and I now have 392's in an A5 and the car flyyyys
Well I'm confused now (not uncommon, LOL), are you saying you REMOVED the LTs and replaced with 392 mans/mids? If so you have proven my point as I have a set of 392 mans/mids and to connect to my 2.5" ATAX I would have to convert the connection at mids/cat back down to 2.5" from 2.75" but was going to REMOVE the last 1.5" of the mid pipes before welding a reducer to it because the mids "neck down" to LESS than 2.5" ID, so you have INCREASED the back pressure compared to the LTs, so if it runs better than with oversized (IMO) LTs and mids now.
 

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are you saying you REMOVED the LTs and replaced with 392 mans/mids?
My impression is he went to a 3.92 rear end gearing with the automatic but i could be wrong.

Take it easy
Jay
 

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My impression is he went to a 3.92 rear end gearing with the automatic but i could be wrong.

Take it easy
Jay
Think you are right, thanks read "gear" thought general term not gearing sorry to get thread off subject, my bad.
 
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I just ordered replacement mids and x-pipe for my car as well. I had originally ordered R/T mid and DynoMax catback. After looking at some schematics one day I realised that even though the exhaust is advertised as 3" it actually necks down to 2.5" where is mates up to the mids. This is to fit the stock sized mids and all aftermarket mid are also 2.5" for the R/T. So I ordered the 3" mid pipes from JBA that are for a SRT(they neck down to 2.75"). I also ordered the x-pipe from the SRT DynoMax catback(all other parts are the same) to replace the R/T 2.5" x-pipe. So now my 1 3/4 JBA long tube go into JBA SRT mid pipes, into essentially an SRT DynoMax VT catback. If I read a post like Ghosts earlier I could've saved myself $300 bucks.
 
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