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Thread: LB7 Turbo Downpipe

  1. #1
    Registered User HoytBows's Avatar
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    Default LB7 Turbo Downpipe

    Its my understanding that nobody makes a larger downpipe for the turbo on my truck. First question is why. Second question is somebody going to in the future or has somebody heard of anybody fabricating their own. If the answer to all these questions is no, is the only answer a bigger turbo?

    The whole idea of running a 4" or bigger exhaust behind a dinky down pipe bothers me. Seems a little pointless
    -CHAD-

    2009 Chevy CCSB LMM LTZ. EFI Live DSP5. Edge Insight CTS. Diamond Eye 4" Downpipe back. Bilstiens w/ Cranked T-Bars & 2" Blocks. Merchant PCV reroute and EGR Disabled and soon to be blocked. Transgo JR. B&W Turnover ball. Cooper Discoverer ATP. 100K


    2003 Chevy CCSB--> SOLD! Loved that truck tho.

  2. #2
    Cruises comfortably at 140... Unit453's Avatar
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    Diamond Eye makes a downpipe thats supposedly 4" from the turbo down.
    Nick

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    Registered User HoytBows's Avatar
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    I cant find one anywhere on their site for an 03 LB7.....
    -CHAD-

    2009 Chevy CCSB LMM LTZ. EFI Live DSP5. Edge Insight CTS. Diamond Eye 4" Downpipe back. Bilstiens w/ Cranked T-Bars & 2" Blocks. Merchant PCV reroute and EGR Disabled and soon to be blocked. Transgo JR. B&W Turnover ball. Cooper Discoverer ATP. 100K


    2003 Chevy CCSB--> SOLD! Loved that truck tho.

  4. #4
    Doghouse Diesel Performance Cumminalong's Avatar
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    Diamond Eye's downpipe is only 3".

    Part Number: 321056

    The problem with the down pipe is simply the space. There isn't enough clearance the run a 4" downpipe (at least without it being a little custom) in the stock location.

    Even swapping the down pipe without removing the turbo is an act of contorsion.
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    TTS makes what your looking for. There are 2 different models for the LB7 application and they have them both. It's a kit that replaces the downpipe and the front pipe. The downpipe is stepped in size to get it to fit, 3 1/2 to 4". IT's a stainless steel kit.

    http://www.ttspowersystems.com/GM_Diesel_exhaust.html

  6. #6
    McLovin stacks04's Avatar
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    i honestly dont see it making much of a power gain to justify 700 dollars. you could buy efi live for that and get a butt load more power even on the stock exhaust then with the down pipe.
    GOD PLEASE HELP THE USA.
    Those that make peaceful revolution impossible, make violent revolution inevitable.


    Oh Lord, I would live my life in freedom, peace and happiness, enjoying the simple pleasures of hearth and home. I would die an old, old man in my own bed, After a life of enjoying your blessings.
    But if that is not to be, Lord, if monsters should find their way to this corner of the world on my watch, then help me to sweep those bastards from the ramparts, because doing that is good, and right, and just.
    And if in this I should fall, let me be found atop a pile of brass, behind the wall I made of their corpses.

  7. #7
    FRANKENBURBAN THEFERMANATOR's Avatar
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    I believe they said that an upgraded downpipe won't make much of a difference so long as you're running the stock turbo. The stock downpipe can easily support whatever it can flow.
    WHO SAYS YOU CAN'T HAVE IT ALL, JUST BUILD IT

    1995 GMC 2500 SUBURBAN powered by 01 DURAMAX/ALLISON, little of this, a little of that,
    DIAMONDEYE 4" exhaust, CORSA muffler, AFE stage 1 dry filter, custom tuning by me, KENNEDY single pump and pump rub kit.


  8. #8
    Doghouse Diesel Performance Cumminalong's Avatar
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    Here's the problem with doing that.....

    Your exhaust is only as efficient as the smallest restriction.

    The exhaust needs to be the largest where it's the hottest and moving the fastest, which is right at the turbo.

    After that, the exhaust cools and condenses extremely fast so stepping up to the 4" beyond that is kind of a waste. It actually needs to get smaller to maintain efficiency. If it was 4" off the turbo and then stepping to a 3.5" after the muffler, you'd be better off.

    Without having it as a true 4" (or at least 3.5") you're not making any significant gain for the money you spend.

    And yes, a TRUE 4" system will make an impact. If you look at the voume of air that a 6.6L, forced induction motor can move, it FAR exceeds what a 3.5" exhaust can support on the upper end.

    Even my 5.9 is over the volume of what a 4" can flow on the top end, and that's with a stock turbo.
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  9. #9
    McLovin stacks04's Avatar
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    Quote Originally Posted by Cumminalong View Post
    Here's the problem with doing that.....

    Your exhaust is only as efficient as the smallest restriction.

    The exhaust needs to be the largest where it's the hottest and moving the fastest, which is right at the turbo.

    After that, the exhaust cools and condenses extremely fast so stepping up to the 4" beyond that is kind of a waste. It actually needs to get smaller to maintain efficiency. If it was 4" off the turbo and then stepping to a 3.5" after the muffler, you'd be better off.

    Without having it as a true 4" (or at least 3.5") you're not making any significant gain for the money you spend.

    And yes, a TRUE 4" system will make an impact. If you look at the voume of air that a 6.6L, forced induction motor can move, it FAR exceeds what a 3.5" exhaust can support on the upper end.

    Even my 5.9 is over the volume of what a 4" can flow on the top end, and that's with a stock turbo.
    not bustin balls, but show me some dyno numbers on an otherwise stock truck to support that theory. and justify 700 bucks. the diamond eye pipe is about as big as a dmax will hold without major modification and most every report is it helps temps, but doesnt really effect power until upper rpms. rpms most guys on stock internals will never see. this is on tuned or non tuned trucks.
    GOD PLEASE HELP THE USA.
    Those that make peaceful revolution impossible, make violent revolution inevitable.


    Oh Lord, I would live my life in freedom, peace and happiness, enjoying the simple pleasures of hearth and home. I would die an old, old man in my own bed, After a life of enjoying your blessings.
    But if that is not to be, Lord, if monsters should find their way to this corner of the world on my watch, then help me to sweep those bastards from the ramparts, because doing that is good, and right, and just.
    And if in this I should fall, let me be found atop a pile of brass, behind the wall I made of their corpses.

  10. #10
    Diesel Weasel Mad Maxx's Avatar
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    James

    '07 Chevy Silverado 2500HD CCSB LBZ
    '06 Dodge Ram 2500 QCLB Cummins
    '06 Jeep Liberty CRD


  11. #11
    Doghouse Diesel Performance Cumminalong's Avatar
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    Quote Originally Posted by stacks04 View Post
    not bustin balls, but show me some dyno numbers on an otherwise stock truck to support that theory. and justify 700 bucks. the diamond eye pipe is about as big as a dmax will hold without major modification and most every report is it helps temps, but doesnt really effect power until upper rpms. rpms most guys on stock internals will never see. this is on tuned or non tuned trucks.

    On an otherwise stock truck, you'll never notice it.

    But yes, that is the theory.

    Here's a little redneck thermodynamics for you, tell me where I'm flawed.

    Hot air under pressure = expanded volume and high velocity, which means a necessity for increased pipe diameter so as not to increase backpressure.

    Cooler air under decreasing pressure = condensed and lower velocity, which means you need a smaller diameter pipe to maintain the same velocity.

    The key to the exhaust is maintaining the velocity and not creating so much space that the air tumbles in the exhaust, causing backpressure. At the same time you need to have enough pipe to keep from causing a restriction.

    Dyno numbers....got 'em.....742 HP / 1456 lbs of torque. My exhaust goes from 5" from the turbo to 4" at the muffler outlet.

    A 4" exhaust at the turbo on my truck would choke it. 4" pipe can support 1700 - 1900 CFM of air, depending on the temp. At wide open throttle and full boost, I'm pushing 2400 - 2600 CFM of air.

    The shorter the exhaust, the less you need to step down the pipe.

    1200 degrees at the turbo is only 600 - 700 degrees at the tip.

    And $700?....you never asked me for a price.
    Last edited by Cumminalong; 01-27-2010 at 05:52 PM.
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  12. #12
    Registered User HoytBows's Avatar
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    So what im kinda getting is that it would help to have a larger downpipe if my truck was really hopped up. But since it isnt anything crazy I wont be able to notice much of a difference. Which makes me wonder how much better a 4" system will be than my stock straight pipe....
    -CHAD-

    2009 Chevy CCSB LMM LTZ. EFI Live DSP5. Edge Insight CTS. Diamond Eye 4" Downpipe back. Bilstiens w/ Cranked T-Bars & 2" Blocks. Merchant PCV reroute and EGR Disabled and soon to be blocked. Transgo JR. B&W Turnover ball. Cooper Discoverer ATP. 100K


    2003 Chevy CCSB--> SOLD! Loved that truck tho.

  13. #13
    Diesel Weasel Mad Maxx's Avatar
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    Couple the 4" Exhaust with the Downpipe and you WILL Feel a Difference.

    ...and I'm not Kockin "Cumminalong" but a Straight 6 compared to a V8 is a Totally Different Comparison.

    Not only will you Feel a Difference but you'll See an EGT Drop as well, and a Sound Difference too.
    James

    '07 Chevy Silverado 2500HD CCSB LBZ
    '06 Dodge Ram 2500 QCLB Cummins
    '06 Jeep Liberty CRD


  14. #14
    McLovin stacks04's Avatar
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    Quote Originally Posted by Cumminalong View Post
    On an otherwise stock truck, you'll never notice it.

    But yes, that is the theory.

    Here's a little redneck thermodynamics for you, tell me where I'm flawed.

    Hot air under pressure = expanded volume and high velocity, which means a necessity for increased pipe diameter so as not to increase backpressure.

    Cooler air under decreasing pressure = condensed and lower velocity, which means you need a smaller diameter pipe to maintain the same velocity.

    The key to the exhaust is maintaining the velocity and not creating so much space that the air tumbles in the exhaust, causing backpressure. At the same time you need to have enough pipe to keep from causing a restriction.

    Dyno numbers....got 'em.....742 HP / 1456 lbs of torque. My exhaust goes from 5" from the turbo to 4" at the muffler outlet.

    A 4" exhaust at the turbo on my truck would choke it. 4" pipe can support 1700 - 1900 CFM of air, depending on the temp. At wide open throttle and full boost, I'm pushing 2400 - 2600 CFM of air.

    The shorter the exhaust, the less you need to step down the pipe.

    1200 degrees at the turbo is only 600 - 700 degrees at the tip.

    And $700?....you never asked me for a price.
    those numbers mean absolutely nothing to me. i might be just a tad crazy in saying this, buttttttttttttt i am fairly certain your NOT using the oem turbo in that truck. i am not knockin the performance your getting out of your truck, it is very impressive, but to ever think of reaching those numbers on a stock cummins with stock turbo..... you can put a 10" down pipe on the lb7 turbo, the power to price ratio will never justify 700 bucks. (the link steve cole posted).


    here are the numbers from a tuned dmax. on a newer vvt truck.

    "Made same peak HP as stock pipe on Wendy. But at 3100 rpm starting to show gains. The higher you spin it, the more the gains.

    At 3350rpm the Diamond Eye makes 519rwhp
    At the same RPM, the stocker makes 503rwhp

    So up top, the Diamond Eye will make over 15rwhp gain.

    Move your shift points up to about 3400-3500 to get the most advantage."

    like i said, unless your turning past the rev limiter regularly, the down pipe does not do much on a stock truck by way of power. temps all around do get reduced so for a tow truck it is a diamond eye for 350 is a worthy investment.
    GOD PLEASE HELP THE USA.
    Those that make peaceful revolution impossible, make violent revolution inevitable.


    Oh Lord, I would live my life in freedom, peace and happiness, enjoying the simple pleasures of hearth and home. I would die an old, old man in my own bed, After a life of enjoying your blessings.
    But if that is not to be, Lord, if monsters should find their way to this corner of the world on my watch, then help me to sweep those bastards from the ramparts, because doing that is good, and right, and just.
    And if in this I should fall, let me be found atop a pile of brass, behind the wall I made of their corpses.

  15. #15
    Doghouse Diesel Performance Cumminalong's Avatar
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    Quote Originally Posted by Mad Maxx View Post
    ...and I'm not Kockin "Cumminalong" but a Straight 6 compared to a V8 is a Totally Different Comparison.
    Engine configuration makes ZERO difference to an exhaust pipe. After your exhaust goes into the pedestal and spins the turbo, how many places does it exit the turbo? 1. After mine goes into the turbo and exits, how many places does it come out? 1.

    Pipe is pipe, there is only so many ways to make, bend or shape it.

    Engine volume and total CFM are what dictate exhaust size. I don't care if it's a 12L truck engine or a 2L 4 cylinder, an engine must move a given amount of air. That's all it is, an air pump.

    That air pump is only as efficient as the smallest restriction. If that restriction is right at the turbine discharge, the rest of the system has no impact, unless there is more of a restriction farther down stream (i.e. a muffler)

    Perfect example is a funnel. Take a gallon of water in a bucket and pour it out....it dumps right out. Pour that same gallon of water into a funnel....what happens? It slows down because it has to go through the restriction. Take that same funnel and attach a 4" diameter hose at the end and pour the water into it......Did the water pass through the funnel any faster? Nope.

    Same concept with your exhaust. If you make a restriction, the only way to move the same volume through the smaller opening is to increase pressure (i.e. back pressure).

    Figuring out the RPM range, total CFM, expected exhaust temperature is how you figure out what size piping you need.

    And no, my truck is FAR from stock. What is on my truck is sized for the anticipated air flow requirements.

    On a stock 5.9, a full 4" exhaust works for 3/4 of the RPM range, but at the top (even on a stock truck) it's at it limits. Increase the size of the engine (i.e. 6.6L) or increase the turbo size to a 66 or larger and you're far exceeding what a even a full 4" system can handle on the top end.

    Bottom line is you can make A SECTION of an exhaust larger, but if a previous section is smaller, it's of no benefit. Unless you can get rid of that restriction in the top of that pipe, adding a 4" exhaust is pointless. The best thing to get rid of is the muffler.

    Could this go on and on? Absolutely. The only way to see what it really does is to do a before and after dyno. I think you'll be highly dissapointed in what you get for that amount of money.
    Last edited by Cumminalong; 01-28-2010 at 05:16 PM.
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