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Duramax Third Generation: 2006-2007.5 (LBZ & LLY) Discuss the third generation (2006-2007.5 LBZ & LLY) of the 6.6L Duramax diesel engine & associated components. 2006 LLY engine discussion also belongs in this forum due to the similarities of the 2006 LBZ and the 2006 LLY. Engine related discussion ONLY.

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Old 09-15-2012, 10:39 PM   #1 (permalink)
Tmac0220
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Gutting Cat?

I have a LLY, has anyone ever gutted the cat, then put it back on?
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Old 09-15-2012, 11:18 PM   #2 (permalink)
Maine Towing
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Had a friend do that on his Cummins, used a long pry bar, has worked for quite a while now.
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Old 09-15-2012, 11:31 PM   #3 (permalink)
784x4chev
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I did it to mine before I got a 4" system. If you just use a pry bar or a rod you won't get all of the material out. I cut mine apart and gutted it then re-welded it.
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Old 10-03-2012, 12:38 PM   #4 (permalink)
norcalrider
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Sorry to thread jack, but the guys who gutted theirs, did you pull any codes? did you finger stick? thanks
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Old 10-03-2012, 12:57 PM   #5 (permalink)
1953drtelco
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I gutted the Kitty last year. Your not going to get all the material out but the small amount left will not stop any flow. I used a few steel concrete stakes and short pieces of rebar and a nice 5 lb hammer. It was a 3 beer job with noticeable results. I didn't throw any codes on my LLY, but I'm one of the lucky ones with a FE9 truck in Calif.

It does allow a bit more coal being displayed during the snap test, but not enough to fail the test.
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Old 10-03-2012, 01:17 PM   #6 (permalink)
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IF you're not going to upgrade teh exhaust behind it, you probably won't notice that much of a differance. You'd be surprised at how restrictive the muffler is when you see it in comparison to an aftermarket.
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Old 10-03-2012, 01:34 PM   #7 (permalink)
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I ended up running a 4" exhaust with a Corsa Muffler behind the gutted Kitty. Corsa muffer has a flow through design with no drone at highway speeds....Nice and quiet even when towing
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Old 10-03-2012, 01:58 PM   #8 (permalink)
D_R_C
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Quote:
Originally Posted by Tmac0220 View Post
I have a LLY, has anyone ever gutted the cat, then put it back on?
Do you have to have the cat for emissions?
If not you can get a front pipe for around $120, my Diamond Eye Quiet Tone cost about $135 shipped.
And what is the rest of the exhaust you have on, still stock?

Quote:
Originally Posted by skleppy View Post
IF you're not going to upgrade teh exhaust behind it, you probably won't notice that much of a differance. You'd be surprised at how restrictive the muffler is when you see it in comparison to an aftermarket.

I've been saying this for years but always get blasted from a few.


For the OP,
I have a LMM and first deleted only the muffler, a very noticable difference.
After 3 months I deleted the DPF and left the cat on which helped even more and sounded pretty good.
I ran that way for 3 years, then ditched the cat and went with Diamond Eye Down pipe and Quiet tone front pipe and blocked the egr, there was no real noticable gains considering the cost, except for the a little deeper exhaust sound.

I would first delete the stock muffler, maybe gut the cat or install a aftermarket front pipe. Depending on your emissions laws if they do visual inspections.
You might have to put a aftermarket muffler on to tone it down, if you gut the cat or do a front pipe.
If you leave the cat alone, the exhaust sound should be good without a flow thru muffler.
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Last edited by D_R_C; 10-03-2012 at 02:27 PM.
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Old 12-10-2012, 08:25 AM   #9 (permalink)
dirtymax82
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Quote:
Originally Posted by D_R_C View Post
Do you have to have the cat for emissions?
If not you can get a front pipe for around $120, my Diamond Eye Quiet Tone cost about $135 shipped.
And what is the rest of the exhaust you have on, still stock?



I've been saying this for years but always get blasted from a few.


For the OP,
I have a LMM and first deleted only the muffler, a very noticable difference.
After 3 months I deleted the DPF and left the cat on which helped even more and sounded pretty good.
I ran that way for 3 years, then ditched the cat and went with Diamond Eye Down pipe and Quiet tone front pipe and blocked the egr, there was no real noticable gains considering the cost, except for the a little deeper exhaust sound.

I would first delete the stock muffler, maybe gut the cat or install a aftermarket front pipe. Depending on your emissions laws if they do visual inspections.
You might have to put a aftermarket muffler on to tone it down, if you gut the cat or do a front pipe.
If you leave the cat alone, the exhaust sound should be good without a flow thru muffler.
I have the DPF deleted and have been trying to decide if I want to delete the muffler and cat. I want better flow but don't want to yell inside my truck when I'm pulling my boat. Should I just go with a performance muffler?
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Old 12-10-2012, 09:03 AM   #10 (permalink)
Maine Towing
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I can tell you that my set up is still very quiet in the cab, not any difference from what I can tell, and my truck lives at 26,000 lbs, I was worried about the same thing. Now if I have the back window down and pass a fence, wall, or other object the exhaust reflects off of I can definitely hear a difference, but with the window up there is no difference.
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100 gal Trans-Flo aux tank
B+W Turnover mount, EGR blocked
EFI Live by "Idaho Rob" w/ DSP 5
Lift Pump at 175,000 miles, CP3 at 299,000
ALL ON MOD - credit to GMC2500HD - best $1.29 mod you can get !!!
Air box mod
Wicked hot wife
4" Flo Pro exhaust, down pipe back, cat was stolen by some scrap iron punks That's my story and I'm sticking to it!!!

Official member of the over 300,000 mile club.

Proud Member #880 of the 3500 DUALLY CLUB
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