Exhaust help needed

Robwcormack · June 21, 2019

I need some advice from someone who understands exhaust flow and backpressure much better than I do. I have the 6.2 and I know that the factory exhaust pipe changes diameter several times right around the muffler for some odd reason. I have been considering doing a frankenstein custom exhaust because I have a phenomenal shop in my area that mandrel bends stainless steel and does excellent welding. What I'm looking at doing is cutting out the flappers, GIANT muffler, and both rear resonators and replacing the muffler with a Borla XR-1. Then just do straight pipe for the resonators and to fill the gap from the flappers and extra muffler length. I know that the majority of the factory pipe is right at 3.5", so my question is should I just go with the 3.5" center in/out muffler (40946) or would that eliminate too much back pressure and cause bottom end loss? Would I be better off going with a 3" center in/out (40944) instead, assuming that choking it down at the muffler would create a little more back pressure allowing me to retain the bottom end while still getting the better flow of the straight through muffler? Another thing I'm curious about is since that XR1 muffler is so small would it be a good idea to take one of the resonators from the back that is cut out and have it welded in just behind the muffler? What got me thinking about this is looking at the design of the S-Type system that finally came out for the 6.2. I want it to have a good low rumble but I don't have experience with the XR1 mufflers and I don't want it to be as (obnoxiously in my opinion) loud as the ATAK.

CamGTP · June 21, 2019

Back pressure is not a concern, nor has it ever been.

A factory exhaust system running properly with no flow restrictions do to plugged cats will hardly have any measurable back pressure at all. I bet it's under 1-2 psi at the max.

Some even think installing headers removes back pressure, it's not. It's changing the length of the exhaust tubing to the collector, the size of the inlet on the exhaust header and the shape. Which will also shift the power band of the engine up because it's changing the exhaust pulses and the scavenging effect.

Whatever do will not remove any of the bottom end power the engine already has. Removing the factory muffler and flapper might net a few ponies through the rpm range and possibly improve response.

Billet Bowtie · June 23, 2019

I installed the afe exhaust which is 4" in and dual 3" out. No loss of bottom end. It has a very deep tone to it. Honestly no matter what cat back you choose (or construct) it will probably not net more then 10 hp or so. It's more about the sound your after. The flappers help mask the sound of the engine when it is running on less than 8 cylinders. With the factory exhaust installed I rarely could tell when the DFM was kicking in. With the new exhaust I hear it every time it changes.

Robwcormack · June 24, 2019

On 6/23/2019 at 10:07 AM, Billet Bowtie said:

I installed the afe exhaust which is 4" in and dual 3" out. No loss of bottom end. It has a very deep tone to it. Honestly no matter what cat back you choose (or construct) it will probably not net more then 10 hp or so. It's more about the sound your after. The flappers help mask the sound of the engine when it is running on less than 8 cylinders. With the factory exhaust installed I rarely could tell when the DFM was kicking in. With the new exhaust I hear it every time it changes.

I was worried about the DFM. I've been trying to hold out to make sure Range gets their module done because i'd be pissed if I did the exhaust and they never got to disable the DFM. What's weird is that the factory performance exhaust system doesn't have the flappers and supposedly you can't hear the DFM at all.

I see you're in NC. What part? I'm in Clayton which is about 30 min SE of Raleigh

Billet Bowtie · June 24, 2019

I'm north of Charlotte. I think because the Afe has such a deep tone you hear the changes more. The factory performance exhaust and Corsa have a higher pitch along with being very mild must be why you dont hear the DFM as much.