I'm looking for "the poor man's" mod to decreasing EGT's without having to buy a new exhaust. Is there any benefit to punching some holes in the CAT to increase exhaust flow? If so what is the easiest way to do this? It has to be easy and idiot proof for me to do it! :o: JJ :)

JJ, the replacement down pipes are relatively inexpensive, have you looked into one yet?

Maybe scoring a used LB7 exhaust from someone for cheap?

JJ - by far the easiest way for a fella of your, uh, mechanic ability ;) would be to either find a stock lb7 pipe as ratlover mentioned, or an aftermarket LB7 pipe....either one should bolt right up...just make sure you get the one with the 4 bolt flange on it....then, it's a pretty simple job....

Maybe scoring a used LB7 exhaust from someone for cheap?
I know where I'm getting mine! :lol:

lol......more than likely you can find someone thats had thier stock exhaust in storage for a year or so with 1k miles on it and is tired of storing the damn thing and they may just give it to ya.

Jeff you wana grab it this weekend? Now my mom is tripping over it in her garage and will probably start screetching soon

Edit: I am not positive that its all 100% swap deal. I dont pay much attention to the LLY stuff. I assume its all the same:confused:

Unbolt the 4bolt flange and pull the catback hard to one side with a motorcycle tiedown.

Get a broomstick and violate the intermediate pipe. Most cats are now a ceramic material and bust into dust on impact.

Personally, if you've ever priced a large cat, I just go with the $100-125 aftermarket pipe and save my cat just in case.

sounds like you have violated your cat with a broomstick? or atleast seen it done or know of people that have. You know there are laws against that right?

Violated the cat with a broomstick.:eek: :beerchug: Oh Censored that was funny!!

Seriously. How do you get all the loose parts out. I wouldn't want to go rattling down the road. Could anyone tell if you have performed this so called violation without taking apart the exhaust?

I have seen it done on late model GM gas-engine products. It blows white fragments out the tailpipe. I should have said that in my first post. Sorry.

I replaced my intermediate pipe instead. I may be ghetto, but I'm not a barbarian.

Personally, I would not wreck a $400 cat to save $100.

And yes, the LLY intermediate pipe is the same as the LB7.

Personally, I would not wreck a $400 cat to save $100.
Problem is for us guys that live in states that are sticklers on I/M testing and don't want any dealer hassles.:(

Checked the codes on both trucks today. None. No muffler, no cat, no codes. The change from 3 1/2" to 4" seams to be where mine sets the codes.

JJs DuMax,
I think your best bet would be to just replace the stock muffler. That is where you will get your best bang for the buck.

Checked the codes on both trucks today. None. No muffler, no cat, no codes. The change from 3 1/2" to 4" seams to be where mine sets the codes.
Rick,

So you are basically straight pipe---how does it sound? I have straight pipe turbo back and want to remove cat next but thought it might be to loud. I think I prefer this to 4" as well to avoid issues.

Thanks,

From what I could see in my cat there are screens in there. Didn't see any thing else.

JJs DuMax,
I think your best bet would be to just replace the stock muffler. That is where you will get your best bang for the buck.
Is the stock muffler very restrictive? Makes sense to replace it if it is. Has anyone tried this with verifiable results? JJ :)

It is more restrictive than the cat.

Jumper357, It is not as loud as my wife's LB7 with a 4" and muffler. The smaller pipe combined with the LLY's differant turbo help keep it quiet. You do hear the "vacuum cleaner" sound alot when you are under a load. I would say that soundwise it is about the same as a gas engine with dual exhaust, like a corvette. You do not have that terrible type sound the Do*ge boys make when they are straight piped. It is loud enough to get noticed, and quiet enough not to get noticed to much by the law.

JJ, I put a straight pipe in where the muffler was when I still had the "cat" on. The differance was almost nothing. I then put the LB7 intermediate pipe on and put the muffler back on. Now it was slightly louder. Seamed that the cat was more of a restriction than the muffler. Then we replaced the stock muffler with a Flowmaster. Starting to sound good now. Finally we took off the muffler completely. Normal driving and I love it. Heavy loads I don't know yet. I am susposed to leave for Tucson tommorow with doubles. I will let you know how it does. I could probrably do a recording of it if somebody wanted to hear it.

Best of all NO CODES, so far!

Am I correct that taking the muffler off isn't against the law, but the CAT is? :rolleyes:

If the truck isn't too loud without the muffler then that sounds like the legit way to go. Just straightpipe it? RDL, it isn't too loud? JJ :)

Whether you need a muffler or not is controlled by local sound ordinances. Even a straight piped Dmax is not going to get you a ticket.

Removing the cat is illegal in all 50 states now, IIRC. But so is driving 100mph.

I can do this! :rolleyes: Every time I utter those words I think about Jeff Foxworthy's "You know you're a redneck if your granddaddy's last words were "Watch this!" ):h ):h ):h ):h Ol JJ tends to get in over his head pretty easy! :(

So what kind of places carry the straightpipe I need to do this? Pep Boys? Discount Auto Parts? NAPA? .... JJ :)

JJ, bypassing the muffler only seamed about 10% louder. I did not have a gauge then, so I can't tell you what it did for EGT's. I used parts of my old 2001's stock exhaust to replace it. Doing it this way required some welding, but I did it myself. I was hoping one of the vendors here would come up with a do it yourself kit to do this, but so far nobody has. Removing the cat and leaving the muffler was about 30% louder. This leads me to believe the cat is the most restrictive of the 2. Removing both puts us about 40% louder, yet stll quieter then my wife's LB7 with the 4" system.

When I put my cat back system(strait through muffler) on. I notice a much larger volume of air coming out vs stock muffler. I later replaced the cat. Didn't notice much difference other than audible volume and some minor egt's. Unfortunately I was one of the unlucky LB7 owner with fed emissions.

NEW TO THIS SITE BUT HAVE BEEN WITH ANOTHER FOR OVER A YEAR AND ALMOST ALL ARE RUNNING FROM THERE TURBO TO TAIL WITH A MINIMUM OF 3" PIPE NO CAT NO MUFFLER ON 1500S TO 3500S A BIT NOISIER THAN YOU WOULD WANT BUT THE BENNIFITS OUTWAY THE NOISE AND AS LONG AS YOU KEEP UP ON YOUR OIL CHANGES AND MAINTANE YOUR VEHICLE IT DOES NOT POLLUT ANYMORE THAN IF ALL THAT JUNK WAS ON THERE DIESELS HAVE TO BREATH IN ORDER TO PERFORM CORRECTLY UNLIKE GASSERS NEED A BIT OF BACK PRESSURE. MY STATE DOES NOT REQUIRE EMISIONS TEST ON LIGHT DUTY DIESELS BUT THE CAT IS STILL A LAW THING SO GUT IT OUT AND THEY WILL NEVER NOW. JUST MY THOUGHT AND OTHERS FROM OTHER FORM SITE.-:t

Even a straight piped Dmax is not going to get you a ticket.


Wana put some money on that, I gota little peice of paper that says your wrong;)

I have a 4"-5" exhaust on a programed LB7 so its likely to make a bit more noise though.

Most guys say they were able to find a muff shop to do it for them for 60$ or so. If your going to do it yourself you need a welder and or some other stuff to get it done.

If its too loud or you dont like the sound you could get a muffler put in its place for probably not much more than what you paid the first time. Or get a used exhaust off a truck and bolt up another stocker. or buy aftermarket. If its too quiet you can then ditch the kitty or violate it.

I stand corrected! :p

Our LLY is not that loud with a 100% 4" straight pipe. It does "scream" at WOT under load, but sound is not as loud as our Vette was bone stock at 6500RPM. Comparable to a diesel tractor pulling a load up a steep grade.

I was supprised how much quieter the LLY is than the LB7. Must be the new turbo that helps quiet it down.

Just razzing ya;)

Programing plays a big role also.....louder with the juice than stock and the juice compared to the extreme:eek: My truck is pretty loud and very deep with the 5" tail. Sounds kinda gasserish, very mean sounding. Its not bad inside especially at a cruise or the like but at WOT:eek: I love how it sounds.

:Whoa: BDIESELFLOYD (http://www.dieselplace.com/forum/member.php?u=13354)<SCRIPT type=text/javascript> vbmenu_register("postmenu_489881", true); </SCRIPT> --- BREATHE!!! :Whoa:

Ratlover states "If your going to do it yourself you need a welder and or some other stuff to get it done."

JJ states "Can you say KABOOM?" :eek: Put a welder, heck a bic lighter, in my hands under anything combustible and just watch for the mushroom cloud! ):h

So JJ will be going to a muffler shop. The muffler on these trucks is huge!!! Does the exhaust flow travel straight through or does it make turns? If that is a stupid question then JJ's right on target! :D

I'm going to make some calls this morning. I will ask how much they charge to remove the muffler on a duramax equipped truck and replace it with a 3 1/2" straightpipe. JJ :)

it takes all kinds of funny paths.....

I'm going to make some calls this morning. I will ask how much they charge to remove the muffler on a duramax equipped truck and replace it with a 3 1/2" straightpipe. JJ :)[/QUOTE]

Hey JJ, If you are going to do that, you would probably spend just a little more for the MBRP alumanized cat back system. Very easy to install yourself.

Someone said $60 to cut the muffler off and straightpipe it. Isn't MBRP like $400+? JJ :)

Hm. That's cheaper than I thought, but hey. You can get a MBRP Alumanized for aroung $300. $300 - $60 = $240. For a measly $240 more you can have a sweat cat back system):h . That's how I explain things to my wife anyways.

Unfortanately, My wife would say, " you could spend that $240 on me and my truck". Thats why she has a 4" system and I have a straight pipe.

I know what you mean. Come to think of it. I'm spending all this money on MY truck, but I drive it about 10% of the time. Hmm, I think I've been had:Wedgie:

Mama JJ flat out calls it "her truck"! She does let me pump the diesel, air up the tires, etc. She's so sweet!


RDL, you fired up the stove yet? JJ :o:

Sollly, I think I've been had TOO, but it's still fun.

JJ, you said something somewhere about a "bic lighter" and a mushroom cloud. You didn't happen to hold it under you EGT probe for me, did you?? I did do the boiling water thing and it checked good. Waiting on infa-red thermometer now.

RDL, I pulled the 5ver this past weekend up through SC and into NE GA. No mountains but a few good, long climbs. My EGT's usually went up to 1100-1200 on any significant climbs without pushing the LLY too hard and increasing boost. The highest EGT I saw was 1287*, highest boost was 17.6. Outside temp was 41* with about 50% humidity. I'm guesstimating the 5ver weighed in somewhere around 16500-17000 lbs.

I'm going after exhaust mods before WI since the WI kicks in above 16psi boost. I only went above 16psi boost on a few hills. I'm still going to put WI on my truck, but for now the exhaust appears to provide the more immediate benefit. I didn't see where anyone posted how to "gut" the CAT, though I did see a reference to drilling a 4" hole or something to that affect.

Front runner right now is the MBRP 4" TS409 from dieselperformanceparts. I'm also looking at the 5" summit. It may just come down to price. Later. JJ :)