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Discussion Starter #1
I know there have been countless write ups on how best to remove the stock downpipe without removing gearbox etc etc, but I though I'd share my experience, as it actually worked out pretty good.

First tools. I bought a set of 'S' shape 12 point ring spanners, 12 point ½" drive sockets, you'll need 12 & 14mm, length of chain, 2x screw pin U shackles, crow bar and a hearty breakfast!!!!!

I started by removing resonator, air intake pipe, then the heat shield on top of the turbo. Passenger side tire, wheel arch cover and proceeded to remove the 2 bolts that hold the transmission dipstick tube, the OEM downpipe heat shield and finally loosened and removed the ring binder holding the downpipe to the exhaust. All these item are really quite easy to remove and should not take you too long.

Now the fun begins, the 4x 12 point 12mm bolts and 2x 14mm nuts that hold the downpipe on.
Somewhere I read, that using the chain and screw pin U shackle attached to the other end of the S spanner, running the chain down along the transmission and then pulling on it from below will give you the leverage to loosen the 12 point bolts.
So I proceeded to try that, but found that I just could not get enough pulling force on the chain.
Instead, I got my crow bar, attached another screw pin U shackle to it, then attached the lower end of the chain to the crow bard via the U shackle and using the drivers side torsion bar as a pivot point for the crow bar pulling on the chain, I was able to loosen ALL top 3x 12 point 12mm bolts and the 14mm nuts. For some reason, I could not get the right angle for the last 12mm 12 point bolt at the bottom-middle of the downpipe to pull it loose with the chain/crow bar method, so I ended up using the OEM bottle jack to push down on the S spanner, jamming in up against the top end of the firewall, that did the trick!
So, now I had ALL nuts & bolts removed from the downpipe!

The next challenge was trying to pull the OEM downpipe through the bottom.
Its tight, REALLY tight. So after some thought and trial, I realized that the passenger side up pipe is in the way. I pushed the downpipe out of the way, pushing it all the way up as far as it goes, then simply removed the 6x 12mm 12 pin bolts holding the up pipe on, access was easy, I used a ½" drive socket and a steel pipe for leverage, they all came out pretty easy.
The OEM downpipe now came out really easy, presto!!

I proceeded to put the 3" MBRP downpipe up into the cavity between engine and firewall, re installed the up pipe, bolted downpipe back on, then transmission dip stick tube, re connected the exhaust and the rest is pretty straight forward.
With the above method, there is no need to heat the bolts, or use any kind of lubricant to try and loosen the downpipe bolts.
Allow a few hours, I spent a Sunday doing all this, taking my time :)

I hope this will help some guys changing your OEM downpipe with a larger 3" after market unit.
 

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Good info! I used a ratchet strap from the wrench down through the firewall and hooked it to my boat...then stood on the strap to break them.. took me all day also:D

03' Silverado CC/SB Stock
 

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I wish you could have wrote this a few months ago.... I successfully changed mine but it took a lot of cussing, heating, pb blaster, wrench throwing, heating, and finally once the bolts broke loose it was a breeze
 

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cool, sry to brag but I did mine sitting on my tranny.........cab was off, lol
nascar style with the impact gun!
 

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so was all that head eak worth the power or egt drop that it gave you? I have been told its not really worth doing is that true?
 

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Discussion Starter #6
so was all that head eak worth the power or egt drop that it gave you? I have been told its not really worth doing is that true?
don't expect miracles, but, I think it is worth overall if you also do other mods, such as better flowing headers and up pipes, I am sure that the sum of all these mods, including tuning etc will make a difference, there is no doubt about it.
My EGT's have dropped just a little, nothing huge, but as I've said above, the sum of all the different mods one can do, will make a difference for sure.
 

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I think its worth it if you plan on sticking with a stock turbo. If not pocket the money and put it towards the turbo you want in the future. If I had to do it all again I would of saved the 600-700 I spent on an intake, horn and downpipe and put toward a s366 or 466 lol jmo
 

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Discussion Starter #9
I also do believe that helping an engine breath better/improve air flow, for in coming air as well as exhaust, is always beneficial to the overall performance.
 

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I also do believe that helping an engine breath better/improve air flow, for in coming air as well as exhaust, is always beneficial to the overall performance.
Depends your goals. Probably not that much benefit for a guy just looking for a few econ tunes and mild HP.
 

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Discussion Starter #11
Depends your goals. Probably not that much benefit for a guy just looking for a few econ tunes and mild HP.
have to disagree, improving general air flow, be it gas or diesel, will have benefits, sometimes only small, sometimes quite large, all of course depending on other mods etc
 

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have to disagree, improving general air flow, be it gas or diesel, will have benefits, sometimes only small, sometimes quite large, all of course depending on other mods etc
How much benefit though for the average Joe wanting no more than 80hp over stock? Not enough benefit to out weight the cost. Improving airflow is great and all, but if you don't need more air...what's the point? Just like the guys trying to up the boost on small tunes when not needed...no point. You dont always need more air if you arent pushing enough fuel...I could see an intake MAYBE just because the lb7 intakes suck but a DP is pointless. The stock exhaust and downpipe are suffiecent enough for small tunes
 

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I ended up selling my profab downpipe after messing with it and stripping on of the bolts... it's reall not worth the hassle... but it towards efi live or save for tranny.
 

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Discussion Starter #14
having a set of reasonable quality tools also goes a long way, Target or WALMART tools are really not suitable for a job like this.
Not saying that any on this thread use cheap tools, but I've learned the hard way over the years.
Another important factor is patience and taking ones time, not easy to have when things are tight and just downright shitty, when I loose it, I walk away, time out, think about it and then get back to it, its amazing how after some time out all of a sudden it falls into place. :neener
 

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When i rebuilt my Lb7 i went back with a 50 over block, 100Hp Industrial racing injectors, alternating cam, 64 mm stealth turbo, 4 inch off road stainless racing exhaust and EFI Live by Industrial Injection. I heard replacing that down pipes a bitch to change. So two questions. Will it make any performance difference and I have the heat wrapped 3 inch MSRP down pipe. Do you still need that pain in the ass heat shield. Thanks for the comme nb ts in advance
 

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When i rebuilt my Lb7 i went back with a 50 over block, 100Hp Industrial racing injectors, alternating cam, 64 mm stealth turbo, 4 inch off road stainless racing exhaust and EFI Live by Industrial Injection. I heard replacing that down pipes a bitch to change. So two questions. Will it make any performance difference and I have the heat wrapped 3 inch MSRP down pipe. Do you still need that pain in the ass heat shield. Thanks for the comme nb ts in advance
If you’ve got everything back together I’d forget it, unless your literally trying to squeeze every ounce of power out that you can, if you pull the motor/cab again yeah go for it, 1628% easier
 
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