Originally Posted by 4x4ord
I was told that the stock muffler does very little sound deadening once the DPF and cat are removed.
This is correct, we have tested a bunch of different combinations of pipe sizes from 4" inch to 5" along with straight pipe downpipe back systems, our CAT/DPF/UREA delete pipes, to our delete pipes with aftermarket DPF back exhaust kits. The stock muffler does a better job removing hissing sounds then no muffler at all like the straight pipe downpipe back kits. The best combination we found so far IMO is a custom 4 to 5" CAT/DPF/UREA delete pipe built to run a 08-10 6.4 Magnaflow 5" DPF back kit with full size muffler. It may sound confusing but bolts right on and sounds great. We had this setup on the truck that went to Rudy's in NC this week for the open house/shoot out. It is completely reverseable for dealer visits if needed.