Hey there,

I have to say that I love this forum! Lots of good info.

I will be installing a CAI in my 2004 GTP Comp G this weekend and now the bug has hit me and the next logical step would be a new downpipe and a cat back ..right? There are many options out there and I have been reading some of the posts about some of the dp and cat back systems not meeting emissions. I am in N.C. and we have emissions tests as part of the yearly inspection, so what would be a good dp and cat back combo to get to help improve performance, while maintaining emissions?

Thanks for the help!

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2009 G8 GT -Sport and Premium Pkgs, Roto-Fab CAI, Cortex 93 Octane Tune, Billet Prototype Catch Can, BMR Front and Rear Sways, BMR RTAs, BMR Rear Cradle Bushings, BMR Steering Rack Bushing, GXP SW......and much more to come.

Most would te u to skip the downpipe and go with headers...headers can be purchased for aboutthe same price and you'll have higher gains. You can also change ur plus and wires (autolites) is recommeded and change your tstat to a 180 and i would suggest get something to scan the knock with a aeroforce scan gauge before u start going crazy modding.

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Catbacks are useless unless you want to waste money and see no gains, but a little extra racket. Matt is right, Headers> DP... Especially if you decide down the road to get headers, your DP is uselss as the headers come with a DP of their own due to the headers rear primaries and crossover pipe hanging a lot lower in the exhaust tunnel

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1998 GTP (L32 swap) | 2000 SE (L67 swapped)

Why buy something sensible with a RWD setup when you can build something really stupid, like this

Hey there!

Thanks for the tips. I am still learning and this site is a great resource. So if I get the headers/dp combo how will I know which ones will allow me to pass NC emissions? What should I be aware of? Sizing? Any suggestions of headers? Thanks.

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2009 G8 GT -Sport and Premium Pkgs, Roto-Fab CAI, Cortex 93 Octane Tune, Billet Prototype Catch Can, BMR Front and Rear Sways, BMR RTAs, BMR Rear Cradle Bushings, BMR Steering Rack Bushing, GXP SW......and much more to come.

That's a tough one. Out here in CA it's pretty strict, but have had buddies with headers (catted DP) pass just fine, even if it was by the skin of their teeth. If you do go the header route, you can buy some of the higher priced ones like SLP or TOGs and get a carb legal sticker so atleast it won't get you a visual inspection fail. If you know of some shops that don't worry so much about visual, there's a great set on eBay, under the name Speed Daddy, that is essentially an SLP knockoff. Run a cat on your DP and you should be fine

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1998 GTP (L32 swap) | 2000 SE (L67 swapped)

Why buy something sensible with a RWD setup when you can build something really stupid, like this

Thank you! I know I have to do more research but do most aftermartket downpipes not have a Cat? And I see that most headers are 3inch. Is that going to present issues for emissions sniff test? Not worried about visual so much.

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2009 G8 GT -Sport and Premium Pkgs, Roto-Fab CAI, Cortex 93 Octane Tune, Billet Prototype Catch Can, BMR Front and Rear Sways, BMR RTAs, BMR Rear Cradle Bushings, BMR Steering Rack Bushing, GXP SW......and much more to come.

Well not sure about some of the other brands but SSAC/SD/SLP style headers come with a 3 piece DP, 1st piece has flange with a v-band clamp that mates it to the collector. 2nd piece is just a 3" (long) plain pipe, 3rd piece has the hangers and o2 bung and ending with a stock style 2 bolt flange to bolt right up to your stock catback.

Now that 2nd piece is basically there to give you the option of a cat (of course replacing that pipe with a cat and just not using it) 3" highflow cats can be had relatively cheap through ZZP.

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1998 GTP (L32 swap) | 2000 SE (L67 swapped)

Why buy something sensible with a RWD setup when you can build something really stupid, like this

Lots of food for thought!

Thank you!

I hope this does not sound naive, but if I get headers and a downpipe and NOT a highflow cat, and just use my stock cat, then that stock cat becomes the choke point right? Would I be losing the benefits of the new header and downpipe by doing this?

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2009 G8 GT -Sport and Premium Pkgs, Roto-Fab CAI, Cortex 93 Octane Tune, Billet Prototype Catch Can, BMR Front and Rear Sways, BMR RTAs, BMR Rear Cradle Bushings, BMR Steering Rack Bushing, GXP SW......and much more to come.

^ pretty much a bad cat effects so many things believe me I know just replaced mine... Let me ask you this how many miles do you have on your car now? Reason I asked my cat clogged at 70k and GM warrants them till 80k. If your cat goes bad and you decide to take it to dealer... Headers would probably void the warranty. I say if your mileage is up there in numbers just save yourself the hassle and get a magnaflow hi flo cat they're relatively cheap compared to gm cat which on my receipt from dealer with labor cost $640.xx lol

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dont use your stock cat, I did that and it was fried when it came to inspection time. I bought a cat from ZZP and that works fine, to be honest I liked it better when I was running it with no cat. Plus it's not worth cutting up your stock DP for that, in case you need to demod.

Have a look here:

supercharged-3800-l67-l32-f16/dp-for-togs-t19836.html

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2005 GT owner [Non S/C] with a "big DIC".
Two years later and I still love the car.
Thanks Pontiac...Bleen is keen!

Thanks everyone!

My car has about 71K on it now.... How long do cats usually last? Probably 85K just outside the warranty?? So how does someone tell if their cat is clogged?

I guess the lesson learned is ...do not use a stock cat with upgraded headers. But the ultimate question is will a highflow cat, such as the Maganaflow, allow me to pass NC emissions?

So once I purchase all this fine exhaust components...how much would it cost me to get new headers, downpipe and cat installed? Doing it myself may be outside my comfort zone.

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2009 G8 GT -Sport and Premium Pkgs, Roto-Fab CAI, Cortex 93 Octane Tune, Billet Prototype Catch Can, BMR Front and Rear Sways, BMR RTAs, BMR Rear Cradle Bushings, BMR Steering Rack Bushing, GXP SW......and much more to come.

^ mine lasted like 71k. I could tell it went from so many things. One is check engine light. 12 mpg WTF? Could smell the cat clogged. Have a aeroforce scan gauge and scanned the code as far as price to install li would probably put it in a ballpark around 300ish simple because it's fwd and won't be to easy inwould call some local shops for a better estimate and the hiflo cat should not fail emissions but don't quote me since I'm in FL no emissions here

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mine is @ 106k but who know when it went out, I hope the magnaflow cat would pass emissions, I bought it for Cali emissions, I'll let you know if I pass. as for the install, it's pretty easy, just take your time, plenty of write ups on line. I think Dubob had a really good one.

Good day!

I am assuming that the hi flow cat is a bolt-on and can I also assume that the stock cat is a bolt on? or does that need to be cut off?


Also, once everyone gets their new headers and downpipe installed, do you reattach the stock exhaust from the cat on back to rear?

Sorry for all the questions... Just trying to learn here

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2009 G8 GT -Sport and Premium Pkgs, Roto-Fab CAI, Cortex 93 Octane Tune, Billet Prototype Catch Can, BMR Front and Rear Sways, BMR RTAs, BMR Rear Cradle Bushings, BMR Steering Rack Bushing, GXP SW......and much more to come.

Where in NC do you stay? Here in Fayetteville we don't do sniff test just they look to see if a cat is there.

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Hey there,

I am in the Charlotte area and I have not had my car inspected yet. When you move to the state and register your vehicle, you get a 1 year grace period. I need to get my car inspected within the next 2 months. A friend of mine told me that the do a sniff test around here.

I probably will not get headers before then, but I would rather be safe than sorry next year!

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2009 G8 GT -Sport and Premium Pkgs, Roto-Fab CAI, Cortex 93 Octane Tune, Billet Prototype Catch Can, BMR Front and Rear Sways, BMR RTAs, BMR Rear Cradle Bushings, BMR Steering Rack Bushing, GXP SW......and much more to come.