Good day,

A week or so a go I was asking about downpipes/cats/catbacks..etc and got lots of good info from you all. Thanks.

I wish I could do the extire exhaust from headers to cat-back, but I need to save some money and do the things that are easy bolt on items.....the things I can do myself. I would not be able to put on headers myself, and do not know anyone who knows, and do not have the money to pay someone to install.

So I want to get a new bolt-on .....downpipe, hi flo cat, and cat back. I also want to get a dp that allows me the flexibility of getting new headers once money becomes available and still be able to use the dp..etc.

I need some advice on a bolt-on downpipe, cat, and cat-back that will not break the bank. I am not looking for a loud voracious exhaust sound, but just a good efficient exhaust that is better than my stock 04 GTP Comp G .

I also need to understand what sizing....3" or 2.5"?


Thanks! I appreciate the help.

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2009 G8 GT - Roto-Fab CAI, Cortex 93 Octane Tune......next up....suspension.

Go 3" catted DP. Where you get it from is a matter of personal opinion. Since you already have some mods and plan on more, 3" will serve you well.

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Although gold dust is precious, when it gets in your eyes, it obstructs your vision.

Ive heard high flow cats arnt nearly worth the money because the horsepower gains are so miniscule its not even worth paying for. And im not sure it would even make a difference on sound.

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All sho no go...

High flow cats are for states with emissions, but performance is still wanted.

3" is the best size for a supercharged application.

Hoganperformance.com has some good priced downpipes. I personally like this option
http://www.hoganperformance.com/dp13s.htm
Its a little pricey, but it has the option for a cat or to go catless.

For a catback your options are endless. Go on youtube and listen to mufflers and see what sounds the best to you, all aftermarket mufflers have close to the same flow rate depending on the type, straight through is going to be the best.

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Excellent! Thanks! I appreciate the tip.
I am in NC and we have emissions testing here and definately need a cat.

Would I need some sort of an adapter/flange to connect the 3" downpipe to the existing pipe from the headers?

Thanks!

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2009 G8 GT - Roto-Fab CAI, Cortex 93 Octane Tune......next up....suspension.

Downpipes just bolt in, you might want a couple of new exhaust gaskets though, which can be found at your local parts store or ZZP, W-body store, etc...

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If you go headers, make sure you get a downpipe for those specific headers. That's the bitch of this...

And if you're stock and wanna go PLOG, a 3" DP will bolt right up.

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Although gold dust is precious, when it gets in your eyes, it obstructs your vision.

Yes! That is what I need to know.....which downpipes are compatible with which headers.
Any combos that have been used successfully


Ok....what is a PLOG? Please educate me

And what does everyone think about about the ZZP downpipe?

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2009 G8 GT - Roto-Fab CAI, Cortex 93 Octane Tune......next up....suspension.

PLOG is a replacement for the stock front manifold. The rear flows pretty well, so most leave that alone, but the front is another story. It's extremely restrictive and weighs a ton. Some people port them (cut away excess material) and create PEMs (ported exhaust manifolds), but I went the PLOG route and I'm happy with it. Here's a pic:



It appears ZZP doesn't list them anymore? WTF?

As for header specific downpipes, if you use Pacesetter brand headers, you should use the specific downpipe for those headers. If you use ZZP's headers, I THINK (I may be wrong, their site will tell you) you can use the TOG downpipe (The Other Guy's brand). Confusing and annoying, I know.

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Although gold dust is precious, when it gets in your eyes, it obstructs your vision.

downpipes are for either headers OR stock manifolds. at least, i have never seen one for use with either setup. maybe take the money for the catback and use it on headers instead?

and just how restrictive is the existing catback? there may not be much of an improvement with a catback over headers. my own plan is to put headers on and leave my stock exhaust.

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Mine: Black 06 GP GT, TOGS, Overkilled PCM, Wizair CAI, Thrasher MPS, GMPP STB's & T/A's, F-Bodies , next up: 1.9 rockers!

Hers: Red 2011 Cruze LTZ turrrrrrrbo, stock and mad slow.

The existing exhaust really isn't bad. You only NEED to replace it somewhere after you've hit 400 WHP or something like that. Trust me, with the mods you have in mind, it's not gonna even be close. lol I may have 220 WHP now...

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Although gold dust is precious, when it gets in your eyes, it obstructs your vision.

The reason why I did not want to go the header route was that it was beyond my means as a relative newbie and I do not know of a good reliable shop that could install headers here in Charlotte. I approached one shop and they had questions about aftermarket headers for the 04 lacked an EGR. Not even sure what that is.

So in the interest of simplicity..how about I just install a new downpipe and hi-flow cat, 180 deg tstat and a ZZP PCM? How much will that gain me? It would certainly be cheaper!

Then I could purchase the SE front and rear extensions!

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2009 G8 GT - Roto-Fab CAI, Cortex 93 Octane Tune......next up....suspension.

Yeah, get a PEM or PLOG and a 3" ZZP catted downpipe for the stock exhaust. You'll do just fine with that. Then again, you are 04+, which doesn't have the U-bend that the 97-03 cars did... That helps.

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Although gold dust is precious, when it gets in your eyes, it obstructs your vision.

hey there,

So Front PLOG and a 3" hi flo catted downpipe to my stock exhaust.

What size is my stock exhaust?
But now the big issue is where would I get a PLOG??

Would this be a bolt on type thing?

What a pain to scrape a few more hp! LOL

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2009 G8 GT - Roto-Fab CAI, Cortex 93 Octane Tune......next up....suspension.

Stock is 2.5", but the stock DP is smaller. And the PLOG and DP are bolt in, but do take a little while. Do the DP first, as it's a bigger pain in the ass.

I'd check the classifieds on the GP boards (here and wherever else) to find the PLOG. My only thought.

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Although gold dust is precious, when it gets in your eyes, it obstructs your vision.

Good day,

Thanks for the help. I will take a look for some plogs and see what is out there, but if that fails, I think I will get ultimately get headers in the future.

I may do the following bolt-on stuff for now and then in the future get some headers as icing on the cake. It follows one of the ZZP performance packages (#2) . I already have a CAI.

* ZZP 3" performance catted DP - will add ZZP headers in the future and it will match up with the DP, plus ZZP has headers with a EGR. Keep my Stock exhaust.

* 3.6 Pulley - ZZPs modular pulley
* ZZP 1.0 PCM
* Autolite 104s
* 180 deg tsat

I will save up and try do this in the Fall.

Any thoughts on this method??

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2009 G8 GT - Roto-Fab CAI, Cortex 93 Octane Tune......next up....suspension.

Sorry about not getting back to you man, I'll get some pictures today for ya, promise

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I went a similar route: ZZP P-log, crossover, 3" D/P w/cat. It bolted up to the SLP 2.5" exhaust that was already there. The difference was noticable in how loud it was. I bought a Magnaflow res from ZZP and it quieted down some, but the interior resonance went off the chart. After searching every source I could check, I went with Car Chemistry resonator inserts. I got mine at Jegs, Summit also has them. I bought three, 2.5" 3 disk inserts, one in front of the resonator, one at each muffler outlet. Problem solved! And the pipes still sound like a performance car. By the way, it passed emmisions 6 weeks later, with the original O2 sensors. My KR is completely gone too, time for more mods, maybe it's time for the smaller pulley and PCM tune.

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04GTPCompG, 180stat, Hogged out stock intake, 104's, P-Log, 3"D/P w/cat, SLP cat-back w/Magnaflow res, TripleEdge shift kit, HPTuners.

Good day!
Anyone know what kind of headers would mate with a Hogan 3" downpipe? Just seeking all the potential options is all.

Thanks!

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2009 G8 GT - Roto-Fab CAI, Cortex 93 Octane Tune......next up....suspension.

buy the headers before the DP, my headers came with the DP. I think most brands do. I bought pacesetters, been on 3 years no leaks. eBay has some that are pretty inexpensive.

and to answer the question, the hogan DP mates with stock manifolds

Something I can add is if your needing help with header install I kno milestone on here is from the Fayetteville area maybe you can shoot him a message.

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ZZP takes the plog off sometimes when they are going to be out for a while.
It was here.

http://www.zzperformance.com/grand_prix ... &catid=110

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'05 Grand Prix GTP Comp G. PLOG, 3" DP, ZZP PCM, K&N Drop in Filter, ZZP strut braces,
10.4 wires, cooler plugs, 3.5 dual SS tips, SPO Spoiler, 180 thermostat, ZZP MPS 3.6 pulley,
F-Body brakes, 18" Moda wheels with 235/50ZR18 Conti DW..

ZZP is out of the Powerlog and will get them back in about 5 weeks. Looks like an easy install. Would you just do only a Powerlog and not a ported rear manifold?

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2009 G8 GT - Roto-Fab CAI, Cortex 93 Octane Tune......next up....suspension.