[15217]

Hi, I was looking to put a new exhaust on my truck. Possibly a front pipe all the way back or just a cat-back and leave the cat converter to avoid possibly throwing computer codes.

After reading a number of threads, it's not very clear that they do anything other than look good and potentially make more noise and turbo whistle.

My primary goal was better fuel economy by allowing the engine to breathe better. I already have an Edge Juice w/attitude set on level 1 and I did the mods to the stock airbox recommended here and am keeping the stock filter because it seems from the test on this web site to, in all reality, do the best job. I am also considering an intake tube (http://www.proguard7direct.com/rpStoreFront/Scripts/prodView.asp?idproduct=982) from AFE. I am of the opinion that a larger/smoother tube would provide better breathing for the engine.

But I'm not sure of the benefits of the exhaust. Would it really help with the mpg's at all? Anybody have any hard data on this? Thanks.

 

[OneTALLGMC96]

IIRC, there is a dyno chart on John Kennedy's Website regarding exhaust. www.Kennedydiesel.com

 

[DSTRBD]

You will definately see a gain with a cat-back system as the biggest restriction in the system (muffler) is replaced with a much higher flowing unit. The diameter of the piping is also increased from 3.5 in. to 4 in. There is also a small gain by pulling the cat, but it is minimal as compared to the cat-back system. Hope this helps.

 

[zank]

Just took muffler off 06 LLY and it looks like at higher speeds better mpg but noise, my wife thinks she can tell so I did not tell her I had it off and she has not said a word. The new turbo on lly don't make as much noise.
So go ahead if you have a LLY and you will be happy. ):h :grd:

 

[zank]

Ps/// My friend on a 03 lb7 on dyno showed more hp with 3.5inch than the dyno shops 4 inch. Like I have seen what most say here only 450 plus hp do you need more than 3.5 inchs. Man if life was like that some of us shorter men would be:cool2: :lol: :grd:

 

[Diesel Tech]

What we have found in all our testing is that replacing the cat back exhaust does help. With that said the question becomes how much for which application. Our answer is that if your looking for the exhaust to give you enough of any one thing, forget it. What the cat back will do is give a little quicker spool up of the turbocharger, lower EGT's 50 - 150 deg., give a slight mileage improvement and change the exhaust sound. When you look at all the things it does we feel it the right thing to change it out. These are the results from a stock truck. Now, if you plan to add power increasing modifications then the affects of the cat back are much greater. We make and sell the quietest aftermarket system on the market, so if you decide a cat back is for you find people who have them in your area and listen to them and pick what fits your needs.

 

[zank]

:exactly:

 

[Bansheezz]

:thumb: Just had TTS installed a cat back system on my truck, sounds like stock and no codes. I'm very happy with it. Thanks Steve

 

[zank]

Took off muffler and replaced with 3.5 inch pipe Tuesday and to day (Friday) went on road and no more noise in cab or out and getting at 60 mph and above 1.5-2 mpg more. O6 LLY
Would tell anyone to cat back or delete muffler.

 

[Mark Craig]

70 gsconvt,

A cat back is a good addition, it'll get you approx 75-80% of the EGT loss and HP gains of a catless system. It'll also be pretty quiet, removing the cat for off road or racing use is the best way to get the lowest EGT's but lots of folks don't want to go that way for legal reasons. The current cats flow great as compared to cats of just a few years ago, not that they aren't restrictive they are just a whole lot less restrictive than the cats from the past. We stock all the MBRP systems in aluminized, 409 and 304 stainless. Singles and duals, call us if you have any questions etc.

Mark @ DPPI

 

[15217]

OK. I've been looking around at everyone's system. I just have one more question: If I buy a cat-back system and it bolts to the cat-converter, does anyone sell a front pipe so that I could remove the catalytic converter and just bolt it to the cat-back system?

My thought is to put a complete system on, but if I start throwing codes, I can put the catalytic converter back on with no difficulty or problems.

 

[Diesel Tech]

Yes, the 2005 cat section is the same length as the 2001 - 2004 LB7 truck without a cat. So just use a 2001 - 2004 LB7 no cat front pipe replacement part and your set.

 

[DMAXSHAWN]

yes it really does help get the front pipe also lowers EGT's and also increases MPG. And most of all the turbo whistles louder.

Shawn

 

[David L51]

Yes, it works! Just my 2Bits.

 

[15217]

OK. Looks like I'll probably be getting a cat-back exhaust system that bolts to the catalytic converter. I'll also probably buy a front/down pipe that would bolt to the cat-back system. This way I can put it on and see how the sound is and if my truck throws the infamous 401/404 codes. This way if I have a problem with codes or don't like the sound, I can put the stock down/front pipe and catalytic back on without any headaches.

Now I just have to find the best price. Any leads there? I'm leaning towards the MBRP 4" 409 stainless system. Seems to be very popular and about what I'm looking for.