Need Advice on Headers for LS3
Thread Starter
Burning Brakes
Joined: Nov 2012
Posts: 1,049
Likes: 1
From: Wisconsin
Need Advice on Headers for LS3
Sorry in advance if this is a repeat of an old thread but I searched and have not been able to find an answer.
I'm considering headers for my '12 GS w/NPP. My goal is to keep the system as quiet and emmission test friendly as possible.
If I use long tube headers, must I replace the stock catalytic converters? Must I also replace the X pipe?
Are "shorty headers" an options?
Thanks in advance.
I'm considering headers for my '12 GS w/NPP. My goal is to keep the system as quiet and emmission test friendly as possible.
If I use long tube headers, must I replace the stock catalytic converters? Must I also replace the X pipe?
Are "shorty headers" an options?
Thanks in advance.
Melting Slicks
Joined: Apr 2007
Posts: 2,987
Likes: 16
From: Phoenix
All long tubes replace the stock cats. Even if you put cats in with long tubes, you are still illegal. I wouldn't waste your time with shorty headers. If you want to pick up an extra 10-15rwhp I would put some factory GM LS7 exhaust manifolds, cats, midpipe, and axleback on your car.
Thread Starter
Burning Brakes
Joined: Nov 2012
Posts: 1,049
Likes: 1
From: Wisconsin
All long tubes replace the stock cats. Even if you put cats in with long tubes, you are still illegal. I wouldn't waste your time with shorty headers. If you want to pick up an extra 10-15rwhp I would put some factory GM LS7 exhaust manifolds, cats, midpipe, and axleback on your car.
Thanks again!
Safety Car
Joined: Jan 2004
Posts: 4,974
Likes: 14
From: Pinellas Park Fl
St. Jude Donor '08-'09 & '12, '14
Thank you very much. Yes, I have read about this modification elsewhere and with your clarification about the long tubes not being street legal, it sounds like it is probably the best way for me to go. May, I ask you this? If I do the LS7 exhaust swap, is there nothing that I can salvage from my Grand Sport exhaust system? Not even the mufflers? I have the NPP system.
Thanks again!
Thanks again!
Thread Starter
Burning Brakes
Joined: Nov 2012
Posts: 1,049
Likes: 1
From: Wisconsin
Thank you once again!
Safety Car
Joined: Jan 2004
Posts: 4,974
Likes: 14
From: Pinellas Park Fl
St. Jude Donor '08-'09 & '12, '14
Thank you. Now I am beginning to understand....I think. So the LS7 system uses 3" piping through to the mufflers vs. the 2.5" on the LS3. I might consider doing the work on the X pipe to downsize it to adapt to the LS3 2.5" exhaust (post X pipe) as long as I wouldn't leave any torque or horsepower on the table by doing such. Do you think that would be the case (i.e., I would give up some of the horsepower gain by constricting the pipe diameter to 2.5" post X pipe)?
Thank you once again!
Thank you once again!
Life Time NCM #2196
Joined: Sep 2004
Posts: 82,559
Likes: 1,665
From: Converse TX
I did an entire exhaust off a ZR1 (Z06 same except mufflers until 2011). Our Vette was not an NPP so I added the NPP in a box and quiet when I want and noisy when I want so you would have almost headers without worry about passing smog
Melting Slicks
Joined: Apr 2007
Posts: 2,987
Likes: 16
From: Phoenix
Use the LS7 intermediate pipe and reduce it down by the axle. Back that far I really doubt you'll have any restrictions on the HP at moderate levels. As the exhaust gas cools it slows down so having the 3" to 2.5" will help keep the velocity up. If you decide to cam then you might want to reconsider keeping the stock over the axle stuff.
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Advanced
Joined: Mar 2012
Posts: 56
Likes: 0
From: DALLAS TX
Thank you. Now I am beginning to understand....I think. So the LS7 system uses 3" piping through to the mufflers vs. the 2.5" on the LS3. I might consider doing the work on the X pipe to downsize it to adapt to the LS3 2.5" exhaust (post X pipe) as long as I wouldn't leave any torque or horsepower on the table by doing such. Do you think that would be the case (i.e., I would give up some of the horsepower gain by constricting the pipe diameter to 2.5" post X pipe)?
Thank you once again!
Thank you once again!
Drifting
Joined: Feb 2012
Posts: 1,255
Likes: 66
From: San Luis Obispo, California
I just went through this evaluation process & bought an entire LS7 sytem (w/ 8,000 orig mls) for my '12 GS dry-sump w/ NPP.
I wanted to keep my LS3 exhaust unmodified so I could go back to stock without any issue. I just planned to bring the LS3 mid-pipe & LS7 mide-pipe both into an exhaust shop & for $150 have them match the LS7 midpipe ends (with Walker 3" to 2.5" reducers) to the width/angle of the LS3 midpipe ends, so it would mate right up to my stock NPP's.
In the end I decided to install Pfadt 1-3/4" headers & cat'd midpipe into my 2.5" NPP's, CA smog laws be damned, & will sell this LS7 system. I was told the LS7 system only gives up @ 10 hp to headers, but the sound & extra 50 hp/tq with long-tube headers/tune was too enticing to resist. I also bought factory GM LS7 head gaskets & the only other item to buy would be 24" racetronix o2 extensions. I bought the 12" but used them in my Pfadt install.
I wanted to keep my LS3 exhaust unmodified so I could go back to stock without any issue. I just planned to bring the LS3 mid-pipe & LS7 mide-pipe both into an exhaust shop & for $150 have them match the LS7 midpipe ends (with Walker 3" to 2.5" reducers) to the width/angle of the LS3 midpipe ends, so it would mate right up to my stock NPP's.
In the end I decided to install Pfadt 1-3/4" headers & cat'd midpipe into my 2.5" NPP's, CA smog laws be damned, & will sell this LS7 system. I was told the LS7 system only gives up @ 10 hp to headers, but the sound & extra 50 hp/tq with long-tube headers/tune was too enticing to resist. I also bought factory GM LS7 head gaskets & the only other item to buy would be 24" racetronix o2 extensions. I bought the 12" but used them in my Pfadt install.
Last edited by Bedouin; Feb 4, 2013 at 07:28 PM.