You may try removing the cat first to lower EGTs and still have it quiet. That is what I started with having a federal setup and it did okay. Since that time I removed the muffler and it is louder but not obnoxious with a slight improvement in EGTS.
From what I've seen the 4" with a muffler will be close to what you want if you're serious about lowering EGTs but the stock is going to be the most quiet
Jim

 

I had a shop remove the muffler on a 2005 Duramax back then and I seem to recall it did not get any louder. For whatever that's worth.

They even told me it wouldn't saying the Dmax was so quiet that they don't even need mufflers. They were right.

The cat was left in tact (CA emissions). My buddy wanted his truck "to sound like a diesel" and he was the one that asked me to have it removed. He couldn't tell either saying it sounded the same - too quiet.

 

Go with the 4". Some people say the 5" drones. I've had a 4" MBRP muffler and delete pipe on for a while and its still quiet. When the cat fell off, the truck has a little bit more of a rumble on the LB7 motor. When I changed to the LBZ motor the rumble almost went away. Its still pretty quiet till when I get on it.:HiHi:

 

I've got a 4 inch Diamond Eye QT system on mine. Its supposed to be about the quietest system you can buy. On a LLY or newer duramax maybe so but on a LB7 you will hear it very clearly. It has a nice tone but at highway speeds it will get on your nerves after a while. I swapped out the Diamond Eye muffler for the 48 inch Donaldson muffler and it remained the same except above 2200 rpms it took a little of the edge off. I'm going to reinstall the Diamond Eye muffler ahead of the Donaldson if there is room. Combined with the QT turbo downpipe that will be like having three mufflers in one system. I'm hoping for near stock in cab noise levels.

 

Check my album for the mufflers I've had on my '02 to try and quiet it down, especially in the 1500 to 1800rpm range when pulling. I also built a small resonator to go behind the crossmember that anchors the torsion bars and a resonator end. I got tired of the exhaust noise and put the stock exhaust back on. The Hushpower muffler was the quietest, even quieter than the 2 mufflers welded together, but still to loud for me. My tolerance for noise may be way different then yours, so this is just my experience trying to quiet it down.

Rich

 

Are the downpipes a restriction on lb7's? I dont mind replacing it if it is, but it looks like a lot of work if nothing is to be gained.

RDS i'm not sure how to check your album. What did you think of the hush power over all? did it drone and did it have a nice sound to it? maybe I will get a 4" diamond eye stainless exhaust with muffler and add a Hushpower to it.

I had a 6.5L before the duramax with the diamond eye kit it sounded okay but had to shut off at drive through windows and almost yell to talk at freeway speeds.
When I get the exhaust for the duramax I want to be able to talk on the freeway easily and not have a obnoxious exhaust for people outside my truck. I have noticed the duramax has stinky exhaust(when windows are down or when i get out right after parking) so maybe I will look into a aftermarket cat. That could possibly keep noise down as well I'm guessing.

I recently bought a 2001 suburban for the wife and every time I drive it I fall in love with it. from inside or outside the suburban you cant tell its running. I often have to look at the tach to make sure lol.

Are the QT Diamond Eye kits available in stainless? I see they offer a QT downpipe that list it fits 01-07, but the picture looks like its not a lb7 turbo flange.

 

Moved to Fuel System, Air, Exhaust, & Emissions Upgrades

 

My friend has 4" Diamond eye QT w/muffler & its quiet on the inside. No in cab drone. Still sounds good on the outside.

Or order whatever DP back exhaust kit you want w/o a muffler & add a FTE 30" muffler/resonator. FTE also makes a 17" resonator which youd put as far forward as can be, & add whichever free flow muffler you want or dont add a muffler.

 

Best hands down is the Corsa exhaust. I had MBRP for a while with muffler, no muffler. But has serious drone. I finally picked up a Corsa muffler designed to rid the drone. Works perfect. Still sounds awesome outside the truck, but no more drone.

 

I tow heavy thru the mountains with stock exhaust (minus kitty), Shotgun Bob tune (Duramaxtuner), no EGT problems.
I also like it quiet without drone.

 

I run banks 4" monster exhaust cat back. It's very quiet has a deep rumble, and when towing the wife didn't even know I changed it. It's been on the truck for 8 years with no problems

 

I run banks 4" monster exhaust cat back. It's very quiet has a deep rumble, and when towing the wife didn't even know I changed it. It's been on the truck for 8 years with no problems

Sometimes when we're leaving somewhere my wife still goes to get in other similar looking tucks in the parking lot. :hehe: