Sierra 6.2L exhaust

[Red Zone 4x4]

I want to cut out the muffler & weld in a throaty muffler or some straight pipe, like I did in my 5.4L Ford. Question is "if anyone has done this or replaced just the muffler; what is the inlet/outlet OD & did you take out the back pressure flap as well?"

[ftwhite]

I cut out the OEM and replaced with MagnaFlow 12909. About 30k miles ago on my 6.2l 2018. I took out the flapper but left the resonator. Its definitely throaty, but not loud. I've considered removing resonator, but not there yet.

[2018GMC]

On 3/14/2020 at 7:35 AM, ftwhite said:

I cut out the OEM and replaced with MagnaFlow 12909. About 30k miles ago on my 6.2l 2018. I took out the flapper but left the resonator. Its definitely throaty, but not loud. I've considered removing resonator, but not there yet.

I did the same thing but with the 14909 100% stainless vs 12909. removed flapper kept resonator. Direct swap. Have muffler shop chop stock muffler out and weld new in. 
 

sounds mellow and nearly stock at cruise. Cold starts and anything above 1/2 throttle or 3k rpm it sounds like a proper v8. 
 

im keeping resonator since it is flow through and helps eliminate drone. 

[AdioSS]

I had the shop cut out the old muffler after the flap since I’m keeping AFM & weld in a bit of 3” straight pipe, but kept the resonator. Big difference in sound when you get on it, but not too loud. You’d probably prefer to cut the resonator out.