I used an OEM 4" from an 08 Duramax. All that was needed was to take 4" out from behind the axle to bring it up and in and I had to make a piece to go from the Y pipe to the flange on the muffler.



Here is a clip of it doing a 4-3-2 manual downshift then full throttle from 35 mph:
Lysholm Silverado - YouTube

 

What year is your truck Dick?

 

Nice sound clips...thanks for those.

 

It's a 2010

 

I have yet to hear a straight through 4" exhaust on a gasser that was quiet. Reasonable, sure. Quiet, no. I am after a straight through desogn 3.5" exhaust that I can make quiet, I'll report back when its done.

 

Mine is reasonably quiet at idle and almost not noticeable at cruise. Sounds wild at wide open.

 

i have 4 in exhaust only 1 piece had to be welded. on over 500 to the rear.since nobody around here could bend 4in .i order duramax ecsb exhaust for my year truck bolt right hanger and all

 

I used a Diamond Eye 4" diesel system with a Magnaflow 27" muffler (12772), a 4" cutout right after the downpipe, and a Magnaflow 4" diesel cat after the cutout. The kit was mostly direct fit except for one hangar that had to be shortened and I had to connect the downpipe to the catback, and shorted the tail pipe slightly. It was a PITA to get it all lined up though, but once I did it fit nicely. In the end I had like 8' of extra pipe and extra clamps and hangars. Not too shabby for under $300 shipped, and it's stainless! It's K4114S-RP.

No sound clips yet but it has a nice deep rumble, and is quieter inside than my stock y-pipe/cats with a Magnaflow 14" dumped out the side.

 

Did some measuring...waiting on pricing for the Magnaflow 3" Tru-X kit with a pair of 6x18" round mufflers and a pair of turndowns. I already called the shop that built my intercooler piping and they're down to fab this up too.
Gimme a few weeks and we'll see what happens.