GMMG is on. The good, the bad...and the ugly
Thread Starter
TECH Apprentice
Joined: Jan 2006
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From: America, f**k yeah!
Well, I'll drop the rust issue since the pic can't show it well enough but, I'll swear...it's not discoloration. It's crusty bubbly rust. Anyway I guess I'll have to try somewhere else to bend the pipes since the right side is the low side and can't be raised anymore....bummer that a system this expensive requires more bending and sounds quieter than a blowmaster 
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Joined: Nov 2001
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From: I-L-L-I-N-O-I-S
Regarding the sound, trust me, your new GMMG cat-back is NOT quieter than your old Flowmaster crossflow muffer...It may be a little tamer at idle and especially inside the car when cruising around town, but the Flowmaster seems louder because it's notorious for it's increased interior noise level (i.e. droning, etc.). If you have someone drive your car up and down the street while you listen from the outside, I guarantee ya you won't think your exhaust is so quiet. It may not be the loudest set-up, but it sure isn't as tame as you're making it sound. And with both set-ups behind stock manifolds/cats, it's not quieter than a Flowmaster like I said. If anything, GMMG is louder at full throttle.
And as for the crooked tailpipes, yep, I had that problem with this system on both my LS1's and LT1. For some reason, one side always seemed to hang lower than the other. Before anyone says my installers didn't know what they were doing, ummm, no...They did a great job and even tried heating up the pipe of the side hanging to low to bend the exhaust, which helped, but never quite got them as even as they should have been. It also didn't help that I had those expensive, optional oval tips.
Anyway, lesson learned. When level, it's a nice looking system with a very good sound at WOT, but not nearly worth the $$$ they charge (I'd never buy it again; nor recommend it). Besides, my new TD set-up w/ Flowmaster 1-chambers dumped absolutely puts it to shame with the sound/torque.
And as for the crooked tailpipes, yep, I had that problem with this system on both my LS1's and LT1. For some reason, one side always seemed to hang lower than the other. Before anyone says my installers didn't know what they were doing, ummm, no...They did a great job and even tried heating up the pipe of the side hanging to low to bend the exhaust, which helped, but never quite got them as even as they should have been. It also didn't help that I had those expensive, optional oval tips.
Anyway, lesson learned. When level, it's a nice looking system with a very good sound at WOT, but not nearly worth the $$$ they charge (I'd never buy it again; nor recommend it). Besides, my new TD set-up w/ Flowmaster 1-chambers dumped absolutely puts it to shame with the sound/torque.
i still think this GMMG is an over priced cat back.. i could see spending $480.. but $850... wow... i better pick up some serious HP for that cost..
Last edited by GR33N GoblinM6; Mar 23, 2007 at 10:04 AM.
Yea I mean its all in what you want your car for, my camaro I DD and am a poor college student so its not worth it for me, But If I was 30 had a good job, and had a weekend toy like a 02 WS6 or SS with low miles that was mint, yea Id give out 850 for it but thats just me
None of these catbacks fit perfect on every car. My magnaflow didn't. My new corsa didn't either. It took me a full day of fiddling in my driveway and cutting and bending to get my corsa to my standards. Sounds like your installers didn't try too hard.... 
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Joined: Sep 2004
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From: Quad Cities, IL
If they welded it, they should have to adjust it. It comes with clamps included, clamps allow that ease of adjustment. I wouldnt sweat the inside of those tips.
I put mine on in our cramped garage, set it up level, then tightened it down. After the car was driven the system settled with a SLIGHTLY lower left side (driver) tip. It's only noticeable because the tips are so close to the rear fascia. If you can get it adjusted so the left is lower, just get a hose clamp and put it around the rubber hangar, tighten as needed for a level system. Or see if they can just make it level. As long as its level I dont care, I didnt buy it for the looks.
It will get a little louder after a few thousand miles. Even with stock cats & Y, this system isn't quiet by any means.
I also found out that rhino ramps arent tall enough to allow this system to be installed, even if you and another push up from under the car with your legs to extend the suspension. Trust me, we still had to do that even with it up THIS high.
The front tires were blocked, all went well. I'm loving the GMMG, but I actually think I'm going to go with speed inc true duals when I add these.
Get the fitment worked out and you should be happy.
I put mine on in our cramped garage, set it up level, then tightened it down. After the car was driven the system settled with a SLIGHTLY lower left side (driver) tip. It's only noticeable because the tips are so close to the rear fascia. If you can get it adjusted so the left is lower, just get a hose clamp and put it around the rubber hangar, tighten as needed for a level system. Or see if they can just make it level. As long as its level I dont care, I didnt buy it for the looks.
It will get a little louder after a few thousand miles. Even with stock cats & Y, this system isn't quiet by any means.
I also found out that rhino ramps arent tall enough to allow this system to be installed, even if you and another push up from under the car with your legs to extend the suspension. Trust me, we still had to do that even with it up THIS high.
The front tires were blocked, all went well. I'm loving the GMMG, but I actually think I'm going to go with speed inc true duals when I add these.
Get the fitment worked out and you should be happy.
My buddy has the GMMG catback, but he also has pacesetters and AFR heads...his **** **** sound freaking MEAN...he's WS6FirebirdTA00 on here...his car has to be the freaking sickest car I've heard...definately LTs and ORY will improve it!
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This guy has the same problem, might want to pm him to see if hes fixed the problem.
http://www.ls2.com/forums/showthread...highlight=gmmg
http://www.ls2.com/forums/showthread...highlight=gmmg
Originally Posted by 2000LS1Z28
Regarding the sound, trust me, your new GMMG cat-back is NOT quieter than your old Flowmaster crossflow muffer...It may be a little tamer at idle and especially inside the car when cruising around town, but the Flowmaster seems louder because it's notorious for it's increased interior noise level (i.e. droning, etc.). If you have someone drive your car up and down the street while you listen from the outside, I guarantee ya you won't think your exhaust is so quiet. It may not be the loudest set-up, but it sure isn't as tame as you're making it sound. And with both set-ups behind stock manifolds/cats, it's not quieter than a Flowmaster like I said. If anything, GMMG is louder at full throttle.
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Joined: Jun 2005
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From: England
Originally Posted by 8a8mfh
And how do they bend the exhaust with it on the car? They don't, they take it back off.
When I was 16 I watched a guy put true duals on my friends 351W powered pinto. The pipes go on, come off get bent, go on, come off get bent, etc, etc, etc, until it's done and fits perfect.
When I was 16 I watched a guy put true duals on my friends 351W powered pinto. The pipes go on, come off get bent, go on, come off get bent, etc, etc, etc, until it's done and fits perfect.
I like the sound of the GMMG, but in every picture I've seen of it I've always been dissapointed by its appearance.
IMO the Stainless Works Chambered exhaust would have been a better bet, although it might have been a tad quieter until you get Lt's on it.
Joined: Nov 2003
Posts: 6,216
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From: Wichita KS / Rancho San Diego
I have the GMMG and my brother the Flowmaster both on manifolds/cats. I think you may be right that the GMMG is louder at WOT, but around town and at cruise it is quieter.
Originally Posted by 300bhp/ton
Yeah that's how they do it when you are paying for a custom setup, but the GMMG is off the shelf and espcially for that money should fit right without the need to modifiy it, or at least be designed so that it can be adjusted easily.
They just slapped it on, said pay up and get out with your crooked ****.
Not the way I'd have done it or had want done to me.
But it's done now what? Only thing I can think of is to have another shop straighten things up. Or live with the expensive crooked **** exhaust.
Thread Starter
TECH Apprentice
Joined: Jan 2006
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From: America, f**k yeah!
Well, I got into another shop and they adjusted it. Now it hangs level. Much better appearance wise. I'm still regretting the tips. I may put my corsa clones back on. Today I'm enjoying the tone more but, it looks like I will have to shell out another $700+ to get the sound I want. I'm almost wondering if I should have gone with duals.
I'm almost wondering if I should have gone with duals. 
Duals get old real quick if it's your daily driver. And in most states it's illegal to just dump under the car, the pipes need to exit out from under the vehicle. When you get headers you'll really love the sound of it.
I wonder GMMG will say? I'll bet they have some good advice or tips on what to do! I think this exhaust kicks butt and looks sweet. I've bought two of them and the two that I have seen installed needed a little tweaking also. Good luck and I'm sure you'll get it worked out.
I don't know about anyone else, but If I spend $900 on an exhaust, and got that I'd be piisssed.
I got my SLP Loudmouth for $180, all stainless steel 3" and I couldnt be happier.
Good luck to the OP, and don't off the exhaust until you hear it with Headers. I think with some nice longtubes on there you will be alot happier.
And I thought the GMMG tips had a rolled lip?
I got my SLP Loudmouth for $180, all stainless steel 3" and I couldnt be happier.
Good luck to the OP, and don't off the exhaust until you hear it with Headers. I think with some nice longtubes on there you will be alot happier.
And I thought the GMMG tips had a rolled lip?
I love my GMMG, esp with stock manis and stock Y.
I just added LTs and am trying to decide which Y pipe I want, and if I want catted or ORY. I know GMMG sounds nasty with an ORY, but Im wondering how bad the drone is on the highway.
I just added LTs and am trying to decide which Y pipe I want, and if I want catted or ORY. I know GMMG sounds nasty with an ORY, but Im wondering how bad the drone is on the highway.