Does anyone have experience modifying exhaust systems on 2012/2013 models? The reason I asked is that I just learned GM added a second pair of catalytic converters for 2012/2013 C6s that lie just fore the X pipe (see pic below). I planned on upgrading the exhaust on my 2012 GS to a ZR1 system and purchased used ZR1 manifolds and an X pipe (all pre-2012). But now I wonder if the X pipe didn't change in 2012 to accomodate the second pair of cats!

Can I use a pre 2012 ZR1 system without getting busted by the EPA? If I do decide to go with a second pair of cats can can I use the pre-2012 X pipe I purchased?

Thanks in advance for any insight you may be able to provide.

 

I changed the X-pipe on my '12 GS for a '11 one, and it was an exact fit. And cars are identical underneath. At least in '12, only CA required those extra cats, but check your state laws. I doubt anybody would catch that, since car looks OEM with the '11 X-pipe. Main reason to replace in my case was the extra heat in the center console area. NPP open sounds nicer, and saved 8 lbs . Here's a picture of both side by side.



Having said that, I don't recall my '12 having those small resonators. Hmmmm. Just the big cats right after the manifold. Could be wrong, since my memory has seen better days . Picture below seems to agree with that, however. And yes, I drilled the crap out of both bellhousing plastic covers to vent the clutch . Good luck.

 

ELP JC Whatever the system is on the left in your first photograph is the system I have on my '12 GS. I am assuming that the squarish boxes with the ribs are the second pair of cats. From what I've read the change was not California specific. "2012 C6 Corvette Sports Four Cats Instead of Two. EPA Requirements force Chevrolet to add a second set of catalytic converters to the mid-pipes of the 2012 CorvetteIf you were to look under the new 2012 Corvette you might be a little surprised at the exhaust design. The C6 Corvette has, since its release, featured two large catalytic converters on the down-pipes, but in 2012 that had to change due to the increasing stringency of EPA regulations. This has resulted in the installation of a second set of catalytic converters on the stock exhaust's mid-pipe."

Maybe someone else will be able to clarify.

Thanks!

 

I think all '12 corvettes got the extra pair of cats, not just CA.

I think the flange's interface between the LS7 header's/cat'd downpipe, & the flange on the mid pipe, are different on '12-'13's...the ball/socket mating is reversed.

If you already have pre-'12 LS7 manifolds & cat'd downpipe, then you'll want a pre-'12 x or h-pipe. If you have '12-'13 LS7 manifolds & cat'd downpipe then I belive you'll need a '12-'13 X or H-pipe to fit up the ball/socket interface correctly.

Search for forum member Vettldo & see his posts on the subject as he went through the same process/questions.

 

Thanks Bed!

Yes, you are correct about the quad cats. And thanks for the heads up about the down pipes and manifolds and Vettldo. I have both pre-2012 ZR1 manifolds and X Pipe. Now I just need 3" catted down pipes.

I think I'm begging to understand this thanks to you and ELP_JC. All Vettes were quad catted beginning in 2012 to meet Kalifornia emissions. But if you don't live in Kali there should be no problem reverting back to pre-2012 set up. In fact, there is an added incentive to modify the exhaust because I don't care what GM says, the extra 2 cats have to be costing the 2012 and 2013 model year Vettes a couple of horsepower.

Thanks again.

 

Officially, no... but it was. Can't compare California to New Mexico, for example. You could hook up my converted 2012 (to 2011) to an emissions machine (nowadays is pretty much just checked by OBDII though) and it'd pass every single state, maybe with the exception of CA, which has the most stringent specs. That's why the car needed the second set of small cats in order to be a 50-state car, like it is.

 

Rathmullan, to further illustrate the difference between '12-'13 LS3/7/9 cat'd down pipe & x-pipe flange/interface connectors;

Look at the first picture you posted & you'll see that the 3", LS7/9, '12-'13(?) X-pipe has the thicker connection flanges on the x-pipe side, & the thinner curved flanges on the manifold/downpipe side. This also means the 'ball' part of the 'ball/socket' flange connection is now on the x-pipe side, the 'socket' part is now on the downpipe side.

The second picture posted by Elp_JC shows two 2.5" LS3 systems; the '12-'13 x-pipe w/ 2 cats on the left, the pre-'12 on the right, both with the 'socket' mounting flanges on the forward ends, & the thinner mounting plates at the forward ends. The LS3 down pipes (below the manifolds) would have the 'ball' ends, & thicker mounting plates.

Essentially this shows how GM reversed the mounting plates, & the ball/socket flanges interface in '12-'13, likely because they added 2 extra cats to the x-pipes.

I wanted to point all this out for anyone thinking they can easily match '12-'13 x-pipes with pre-'12 cat'd down pipes, or vice versa,...not easily done anymore without serious cutting/welding.

 

Thanks Bed! But I'm not sure I follow? Won't the ZR1 X pipe I bought look just like the system ELP_JC shows on the right hand side of his photo only in 3" diameter? And just like he did won't the flanges bolt right up to the down pipe (be they LS7 or LS9...I haven't purchased those yet) flanges? I do have an automatic transmission and I've heard that their may some finangling I have to do to make it fit. I'm assuming the undercarriage tunnel hasn't changed between 2011 and 2012.

Meanwhile I'd like to keep my LS3 NPP mufflers and I understand that there is no difference between LS3/7/9 mufflers in that the internals are 2.5". My question is where exactly the transition occurs from 3" pipe to 2.5" pipe in the LS7/9 exhaust system?

 

The muff internals are 2.5" on the LS3 & 7 units and 3.0" on the ZR1's. If you look at the exhaust entry of the muffs you will see it snakes down on the LS7 units but not the 3.0" ZR1 units. If you have the ZR1 manis, cats & x-pipe do yourself a favor and get a set of ZR1 muffs to mate up to them.

Side note: You will have to spread the rear of the x-pipe about one inch to accomodate the A6.

Full Disclosure: Most of this info is just regurgitated from this site. I am not a master mechanic but I do turn all of my own wrenches.

FWIW! I'm putting a full ZO6 setup on my LS3.

 

See me comments below & note that all my knowledge is from the forum as well;

-The LS7 cat back necks down to 2.5" as it enters the muffler, & I 'think' the LS9 stays 3" all the way through as Speedforhire said, not 100% sure tho. To use the LS7/9 3" x-pipe with your stock 2.5" catback, you'll need 3"-2.5" reducers, & some bending/welding, to get them to slip over your stock LS3 catback. The rear ends of the LS3 x-pipe are more widely spaced than the LS7/9 x-pipe.

-If you had a manual trans grand sport then I'd recommend buying an LS7 bi-mode catback (& sell your LS3 system) because there'd be no modification, just plug it right in. But since you'll need a muffler shop to adapt your LS7/9 x-pipe to the auto trans, they'll spread out the x-pipe & weld on the reducers as well.

 

Thanks again Bed!

I'm kinda of leaning towards Speedforhire's recommendation of going ***** out (as long as I'm bothering to do this) and getting ZR1 mufflers. Heck, they could be worth a couple of ponies. But by doing so, do you know if I would be losing the Dual Mode exhaust capability that I currently have? I did install the wireless Mild2Wild switch. Thanks in advance and sorry to be a nuisance.

 

It's all good...I'm just paying back all the valuable info I've gotten from so many selfless CF inmates.

Now I'm no exhaust flow expert, but they say you want the x-pipe to stay 3" as far back as possible, for exhaust gasses to maintain speed/velocity as they cool...but you also want some back pressure for torque & power, hence the 2.5" LS3/7 catback would provide that. Both LS7 & 9 systems are dual-mode.

Bottom line is if all the stock Z06 needs is a 2.5" catback then that's all, or possibly more, than enough for the LS3. The LS7 catback may likely cost you less than the LS9 as well. If it were my car I'd prefer to use a 2.5" catback over a 3" catback for the LS3...just my .02

I brought my LS3 & LS7 x-pipes down to a muffler shop so he could see how the LS7 x-pipe would get bent, & how the Walker reducers would be welded/fitted, & he wanted @ $150... That plus the $400 LS7 mani's & cats pushed me to just spend $1,700 on full headers/tune, & I couldn't be happier....but I like it loud.

 

I'm indebted to you now Bed as you just saved me $1,200 which is what I was looking at paying for ZR1 mufflers. You response is concise and logical and even I can understand it.

Sometimes I don't think I give the General enough credit. There may be good reason why the Z06's muffler inards are 2.5". Heck, there may be a good reason why the LS3 exhaust piping is 2.5". But I do know that there is no good reason for a second pair of cats beginning in 2012 other than some ruling deliverd by a California EPA bureaucrat. Re: the General, I wondered why the NPP opens at 3500 rpm. Sounds like it may well be an attempt to shape and optimize torque the curve.

I don't know if the Z06/ZR1 manifolds combined with the 3" ZR1 X pipe will buy my LS3 any performance, but given that they have been described as "shorty headers" and that their design was the final innovation that allowed the LS7 to crack 500 hp (guess we'll never know if they added 5 or 15 hp or somewhere in between) I'm willing to take the gamble. If nothing else, maybe I'll realize an improvement in the exhaust note. Thanks again!

 

$1200 for ZR1 muffs? OUCH!

I have a total cost of $800.00 in my full ZO6 setup (to include the gaskets and hardware). I'm happy with the investment and can't wait to get them on. Just too cold this winter to crawl around on the cold concrete to get them on. Springtime is near!

 

Yes Speed, the used ZR1 stuff really commands a premium as there just weren't many ZR1s built relative to Z06s.

But $800 is great! I'm at $550 and I don't even have the down pipes yet!

Please keep me posted on your swap out progress. I'd be curious to get your impressions in terms of change in sound and performance.

Thanks again!

 

No worries...guys have saved me tons of time/money on here too. At the very least I'd ditch the '12 xpipe & get one w/out the 2nd pr of cats. Those LS7/9 manifolds have 4 hydorformed steel runners & flow very well...I saw a universal consensus on CF that you'll get 10-15 hp/tq on an LS3.

Re the ZR1 vs; Z06 bi-mode muffs, I'd read a few posts saying LS3's didn't feel as strong launching with open exhaust, but felt faster when opening @ 3,000-3,500k per normal..makes sense to me. A Tech contributor also reinforced this with a post stating the motor needs that back pressure for initial torque...also makes sense. I've never noticed or cared to know, as I like the open sound so much.

Race bikes have the same issue...open pipes can make top end power, but at the expense of low-grunt torque. A good perforated-core muffler provides just the right mix of initial torque backpressure & wide-open high flow power.

If you do buy used Z06 bi-modes, try to buy the later years '10(??) - '13 as their 'open' pipe through the muffler is solid (non-perforated). Earlier Z06 bi-mode mufflers had a perforated 'open' circuit & were much quieter & you'll see entire threads on the 'Z06 muffler mod' where they cut open the muffler, & cover the perf'd pipe with solid pipe...just not sure what year the factory changed them.

 

Bed: Thanks! One final question.

I've got my Pre-'12 ZR1 X pipe and '10 ZR1 exhaust manifolds and gaskets and I'll get a set of Z06 or ZR1 downpipes when I find em. Assuming I use my LS3 NPP mufflers, when I weld and bolt all this stuff up -- how do I ensure that the dual mode performance exhaust remains functional? I still don't get how the ecm communicates with the ports in the muffler and the exhaust tips. I mean, is there some physical vacuum line that runs inside or outside the pipes that has to get reconnected?

 

Assuming your LS3 has the factory NPP option, everything should bolt right up including the vacuum lines, etc. The optional LS3 NPP system functions the same as the stock LS7/9 systems. Just get pre-'12 cat'd downpipes & you should be fine.

Although...if you were willing to spend $1,200 on ZR1 bi-mode mufflers, then you might consider a set of B&B fusion extremes-Z06 fitment, which would bolt right up. There was a used set for sale on CF not long ago...

However...this thread would settle the question for me...LS3 NPP all the way.
http://forums.corvetteforum.com/c6-t...ffler-mod.html

 

Thanks again Bed! You are among a handful of truly knowledgable and selfless members who really contribute and make this Forum worthwhile and THE BEST AUTO FORUM on the planet. I can't thank you enough, and am PMing this to JimTN a moderator.

As for as the B&B kit, I know you are in to exhaust sound and I appreciate the recommendation. But my wife has sensitive ears so it will be mild2wild in mild mode whenever she's in the passenger seat. Heck, I put a pair of dynomax turbos on my '06 MC 3.9 and she won't ride in the car (except she managed to gladly drive it when here Audi broke down LOL)! THANKS AGAIN! I'll let you know how the mod turns out and will proably bug you with another question or two during the modification process.