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LS4 Performance Grand Prix GXP | Monte Carlo SS | Impala SS | LaCrosse Super

3" Catless Downpipe

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Old Jul 22, 2015 | 09:36 PM
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Default 3" Catless Downpipe
I started putting together the 3" stainless downpipe for my daily GXP. 1/2" stainless flanges at both ends, T304 mandrel bent tubing, and concentric reducer to hook up to the stock catback. I will have some finished photos and sound clip tomorrow...but here are a few teasers.

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Old Jul 22, 2015 | 09:51 PM
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Wow, looks slick. Cant wait for the finished product and the more to come.
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Old Jul 22, 2015 | 09:59 PM
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lol wish i could tig weld
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Old Jul 22, 2015 | 10:01 PM
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Originally Posted by spawne32
lol wish i could tig weld
Only one way to figure it out man. Get or borrow a machine and start burning. I am self taught. Lots of good literature and video help out there.
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Old Jul 22, 2015 | 10:17 PM
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Originally Posted by bfurches
Only one way to figure it out man. Get or borrow a machine and start burning. I am self taught. Lots of good literature and video help out there.
i watch welding tips and tricks religiously lol
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Old Jul 23, 2015 | 08:13 AM
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Originally Posted by spawne32
i watch welding tips and tricks religiously lol
lol i've watched alot of thoes as well... i can decently mig weld now...



nice welds. i'm a big fan of making crap myself vs buying it as well. funny when a downpipe is 150 or so but you could make it with probably 30 dollars in parts.
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Old Jul 23, 2015 | 09:25 AM
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Originally Posted by blkchevyz
nice welds. i'm a big fan of making crap myself vs buying it as well. funny when a downpipe is 150 or so but you could make it with probably 30 dollars in parts.
Unfortunately, these are pretty expensive to assemble if you are using quality stuff. T304 1/2" flanges (which I couldnt find...had to have them water jet), smooth liner flex or bellows, T304 3" stainless mandrel bends, O2 sensor bung, and hanger...All adds up really quick. Unless you are buying in bulk...you arent going to be able to assemble these for less than what ZZP gets.

__________________________________________________ _____________

I came back late last night so I could hammer out the rest of the downpipe uninterrupted. Unfortunately, my new Vibrant 3" bellows haven't shown up yet...so I used a quality lined flex instead for the prototype.

These are the bellows that will be going on my downpipes. I just used them on a turbo build were doing...the quality is awesome.

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Anyways...here is what I came up with...

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Just have to tack the hanger in place.

Quick video of the idle through a stock GXP exhaust...

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Old Jul 23, 2015 | 09:34 AM
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Nice job. Does that car have the factory exhaust, looks big? Also any codes thrown after installation?
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Old Jul 23, 2015 | 09:57 AM
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Originally Posted by rottonj
Nice job. Does that car have the factory exhaust, looks big? Also any codes thrown after installation?
Yes, that is the OE exhaust. Bone stock.

As for codes, I turned off the rear O2 through HP tuners. Otherwise...yes it would have lit off some catalyst efficiency codes.
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Old Jul 23, 2015 | 10:00 AM
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Thanks. Did you notice some decent improvement? Will you be fabricating an exhaust system for the car as well? How about headers? Any other mods you are planning?
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Old Jul 23, 2015 | 01:52 PM
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Can this be had with a CAT?
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Old Jul 23, 2015 | 03:27 PM
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Originally Posted by Mike The Canadian
Can this be had with a CAT?
Absolutely. I would be happy to put any cat of your choosing inline.
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Old Jul 23, 2015 | 03:57 PM
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this piece is redundant if you have headers, i wanna point that out. lol he has a turbo car and is using the cast manifolds so it works in his case. Or on the stock car with the stock manifolds i should say rather.
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Old Jul 23, 2015 | 04:14 PM
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That pipe is on his stock ride, not the race car though. But yea with headers this wont work.
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Old Jul 23, 2015 | 04:29 PM
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Originally Posted by spawne32
this piece is redundant if you have headers, i wanna point that out. lol he has a turbo car and is using the cast manifolds so it works in his case. Or on the stock car with the stock manifolds i should say rather.
Correct, if you have headers this will not work, but as rottonj pointed out...this one is the prototype for the production piece I will be selling. Testing it on my 2008 daily driver GXP.

RottonJ, I fully plan on offering headers, a turbo kit, and two cold air solutions. Lots of exciting stuff in the works for the LS4 platform.
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Old Jul 23, 2015 | 04:45 PM
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Originally Posted by bfurches
Correct, if you have headers this will not work, but as rottonj pointed out...this one is the prototype for the production piece I will be selling. Testing it on my 2008 daily driver GXP.

RottonJ, I fully plan on offering headers, a turbo kit, and two cold air solutions. Lots of exciting stuff in the works for the LS4 platform.
oh sounds exciting shame you cant offer an intake manifold as well lol unless...you can.
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Old Jul 23, 2015 | 06:12 PM
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There is no doubt in my mind he could fab up an intake for our cars, his work is top notch.
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Old Jul 23, 2015 | 06:14 PM
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Originally Posted by bfurches
Correct, if you have headers this will not work, but as rottonj pointed out...this one is the prototype for the production piece I will be selling. Testing it on my 2008 daily driver GXP.

RottonJ, I fully plan on offering headers, a turbo kit, and two cold air solutions. Lots of exciting stuff in the works for the LS4 platform.
This sounds fantastic. You are only about 15 minutes from me and I will defiantly be checking out these prototypes.
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Old Jul 23, 2015 | 06:56 PM
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Originally Posted by rottonj
There is no doubt in my mind he could fab up an intake for our cars, his work is top notch.
Thank you sir.
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Old Jul 23, 2015 | 08:36 PM
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Originally Posted by rottonj
There is no doubt in my mind he could fab up an intake for our cars, his work is top notch.
What's wrong with all the intake options we have now?
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