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2007 CTS-V
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1,002 Posts
Discussion Starter #1
So are there long-tube headers that have high-flow cats that will bolt to my Borla Cat-Back exhaust ?

I want to keep cats on the car.

I really prefer bolt on vs having someone weld.

While I'm on here, should I go with 1-3/4 or 1-7/8 ?
 

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Premium Member
2005 CTS-V
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8,363 Posts
I can't help you on the bolt up cats. I have never understood why if the Corsa catback bolts to the oem cats, and the oem catback bolts to the oem cats, Kooks headers require two different midpipes to connect their headers to the Corsa and oem catbacks. But given that fact, it is unlikely that either of the Kook's midpipes (with cats) will bolt to the Borla eventhough the Borla is a GM certified catback just like the Corsa.

The question of 1 3/4 vs. 1 7/8 headers on LS engines is one of the most hotly debated issues in LS-related internet forums. There are dyno test supporting both choices. There is not a lot of difference in the two sizes in terms of flow - the 1 7/8 primaries will flow 20% more, but that differential is diminished when bolted to 2.5 inch cat back with the length of the V's. If the car is a daily driver the 1 3/4 is probably large enough. If you are trying to reach 500 rwhp someday you would likely want the 1 7/8.
 

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'05 Raven/Ebony CTS-V with toys
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Because the front pipes of the Corsa (and stock) are removed and replaced with the connectors. When it's said that Kooks "bolts" directly to the Corsa catback, it really should be that its slipjoint in front of the resonator is a direct fit. Same for the stock. Therefore its not the bolted end of the catback to the stock cats location (that would be the same regardless of exhaust) where Kooks is a direct fit.

Kooks headers -> Kooks headers for Corsa connectors -> Corsa resonators back to tips
 

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2005 CTS-V
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Because the front pipes of the Corsa (and stock) are removed and replaced with the connectors. When it's said that Kooks "bolts" directly to the Corsa catback, it really should be that its slipjoint in front of the resonator is a direct fit. Same for the stock. Therefore its not the bolted end of the catback to the stock cats location (that would be the same regardless of exhaust) where Kooks is a direct fit.

Kooks headers -> Kooks headers for Corsa connectors -> Corsa resonators back to tips
Thank you for the explantion.
 

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2007 CTS-V
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Discussion Starter #5
Well LT headers may be my next mod; maybe not right away, but next on the list. I'd still like to get a full bolt on kit if possible with high flow cats.

I understand there is not much gain until the car is re-tuned. Is there any harm in installing headers on the stock tune until my 3rd party warranty runs out ?

Other option is: where and how much would a second ecm be ? ebay has them listed for 05's only.
 

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2006 CTS-V
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731 Posts
Yes, you can harm the car. I installed 1 7/8 OBX headers and CAI. When I finally went for the tune, we found I was running dangerously lean. They are not kidding when they say these mods improve air flow!
 

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2005 CTS-V
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The content of this thread so far, confuses me. Typically, those that install headers with no other mods, report running pig-rich - not lean until they get a tune. And, if a 3rd party warranty will tolerate headers, why would it not also tolerate a tweaked PCM?
 

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2016 ATS Premium 6-spd MT
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Having Kooks and Corsa, guess I'm not sure I've ever heard how Kooks and Borla sound in comparison.

Need a vid with audio.
 

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2007 CTS-V
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Discussion Starter #10
The content of this thread so far, confuses me. Typically, those that install headers with no other mods, report running pig-rich - not lean until they get a tune. And, if a 3rd party warranty will tolerate headers, why would it not also tolerate a tweaked PCM?
I asked them about the G-Force axles before I put them in, they said it wouldn't void the warranty unless the axles were the reason for the failure. As long as the headers didn't cause the engine to "fail" I'm sure they would be fine; I do know that a modded pcm will void a warranty if they find out.

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After plenty of youtube searches I believe I may be the guinea-pig as far as headers + Borla.
I really enjoy the refined note I get out of it now, I am just hoping that the headers will amplify the sound. When I was at our Indy meet, I was the quietest one there; other than anyone who was stock.

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Other option is e-cutouts before the mufflers; but I don't really want to cut up the Borla pipes, and I would like the few extra HP from headers and a tune.
 
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