Well I've drooled over this system for long enough. I decided to pick up a GMMG catback system along with a Catco 9118 catalytic converter to replace my old Flowmaster American Thunder and no cat setup. I picked up the GMMG on a group purchase back around Christmas time. Those of you who remember Justin's thread about the GMMG know that it costs quite a bit of money to buy them in Canada. The idea that it costs $850 and that's it is a far cry from reality. So I bought the GMMG with oval tips for $735 US....$894 cdn. Throw on $116 in sales tax and that bumped it up to $1010. Shipping proved to be interesting as it's only free if you live in the USA. I'm in Canada. Too big to ship through USPS and UPS rapes Canadians something fierce on their shipping and brokerage charges. It would have been $300 to ship it to my door with UPS. So I had them ship it to Washington and then re-shipped it to Canada through my own shipping company. Only cost me $40 in shipping that way. I drove to the airport to pick up the GMMG box. IT'S HUGE! 4 feet long, 3 feet wide, and 1.5 feet tall. 56 lbs. The car I was driving, it wouldn't fit in the trunk, back seat, or front seat with seat down. Decided to take it out of the box and it just barely fit in the trunk. There weren't any exhaust hangers with the system. Just 4 clamps. So I wound up buying some brass SLP exhaust hangers from Summit. Part # SLE-30044. They were $57 to purchase and $23 to ship. Another $80. On the bright side, I didn't pay any sales tax on these. The brass looks really nice when you look at it from the left side of the car through the wheel well. It also bolts right in to the stock bolt holes there. Nice. Total bill for the GMMG and cat with install and hangers wound up being: GMMG $894 Catco $175 Sales taxes $138 Shipping $62 SLP hangers $80 Install charge $125 ___________ $1,474. Throw in a half a tank of gas to the airport and back and it's an even $1500. The actual install went pretty good. The muffler section fit in perfectly level the first time. The GMMG intermediate pipe didn't reach the cat, so we used some of my old Flowmaster intermediate pipe to connect the two. The guys in the exhaust shop were pretty impressed with the look of it. They'd never seen a setup like it before. I started the car up and at idle it wasn't too much different than my old Flowmaster setup. I had heard that GMMG is a pretty loud muffler, but I figured that adding a cat would balance out the volume and make it the same as the Flowmaster.....I was wrong. I revved it up a few times in the shop and 20 seconds later, the manager poked his head through the door and said "You know you guys are rattling the windows in here?" Hahahaha. I decided to do some decibel testing before/after. Stock manifolds and Y-pipe, no cat, Flowmaster American Thunder. Idle 72 dB 70 mph 80 dB WOT 88 dB Idle is a cold start inside the garage. 70 mph is in O/D. WOT is measured at 5000 RPM under load. "A" weighted dB scale used. All are done inside the car with the windows closed, radio off, A/C set to OFF. Stock manifolds and Y-pipe, Catco cat, GMMG with oval tips. Idle 73 dB 70 mph 78-80 dB WOT 90 dB A bit louder at idle. Hard to get a good reading on the highway as the second you lift your foot off the gas it's ultra quiet. The Flowmaster was loud all the time on the highway. The WOT figure is misleading. Although 2 dB doesn't sound like much, consider that with the GMMG I'm getting 88 dB at 4000 RPM (the same as the Flowmaster at 5000 RPM) But enough about numbers. How does it sound? It sounds like a lion is in your backseat! And whenever you give it some gas at part throttle or accelerating from a stop light, it gives a lion's roar. Or a lion's growl at light barely moving throttle. I like it. The Flowmaster drone is gone. And it's an intimidating sound for passers by. I've heard pretty much every sound clip of the GMMG on the net that there is. (You have to to justify this cost). And the one thing I can honestly say is if you run it, use a catalytic converter. The GMMG doesn't muffle the sound as much as tune the sound. The cat in effect becomes your muffler. The systems with cats all sounds smooth and exotic. The ones without pop and crack all over the place. Install tip: After bolting in the clamp up by the cat, torch off the bottom of the bolt. It's a long one. The guy putting it in mentioned that on his car, he ran over a plastic bag one time and it melted to his exhaust. Wound up having to sand it all off. Some pictures would be nice. Here it is on the way to the shop to be installed. After getting home. After getting ready to go to a car show. As far as I know, I'm the only GTA owner on the board so far with one of these. And I may be the only Canadian with a 3rd gen GMMG setup. I've never seen another GMMG on anything in real life before. I do know two people in Saskatchewan and Ontario who have them on their 4th gens, but that's it. I suppose a video would be a good idea. Here you go. In the above video, around the 27 second mark you'll hear me rev it to 2000 RPM, then 3000 RPM, then 4000 RPM....then I raise it up to the redline. Another thing is that I can't help but notice the beauty of the chambered muffler when I'm walking back to the car. My Flowmaster muffler was black and hidden from view. All I saw was the tips. But the GMMG is as much eye candy as it is music to your ears.

And I wanted to have the first GTA with a GMMG system on the boards. Oh well. Was it worth the cost to you? I've been drooling over this system for a long time too. Just can't get over the price tag.

Whoa! That thing sounds mean! I want to install the same setup as yours except I want to put 3' chambered pipes straight thru if possible....if not I will go with the crossflow setup! what size pipes are you running? I bet that thing gets even more attention now huh? Good job on the setup!

man ur car sound real nice...a nice tone not to loud either i wish u live n texas so i can hear it n person

Mike, one of the reasons I wanted to go with this setup was that just about everybody runs the same exhaust systems. 80% Flowmaster, 15% Hooker, 5% Magnaflow. I'd also had the Flowmaster for years, so it seemed kinda normal to me. Yeah, the new setup was pretty expensive. But on the other hand, it's stainless so I won't have to worry about future stuff. And I really enjoy driving and looking at it now. I do think it was worth the money in the end. The look on other F-body people's faces when they take a look at it is priceless. It's always the same reaction. What the heck is that?

Seems like every kind of muscle car at car shows have a Flowmaster type setup. After I did the swap to the GMMG, I get quite few more glances and head turns pulling in now. Don't get me wrong. I still like Flowmaster mufflers. But I think they tend to have a 1 dimensional sound. Whereas the GMMG has a deeper rumble down low, an opening of the floodgates around 3000-3500 RPM when you're accelerating and then from there on up, it's half Ferrari half muscle car. I find myself going through the gears with the windows down a lot more now than I did before.

Phoenix, the cat is a 3" in/out, the intermediate is 3", I believe the tailpipes are 2.5". Not really sure what the oval tips work out to be.

I'm not sure what to do about headers. The SuperRam is just begging for headers. But I wonder if it would make things too loud with the GMMG on there. I've been comparing 3rd gen F-body 350 cars that have headers and no cat into muffler as well as headers and cat into muffler. Both setups seem quieter at idle than what I have.

QUOTE]The look on other F-body people's faces when they take a look at it is priceless. It's always the same reaction. What the heck is that?
[/quote]

LOL hahahahaha I bet they end up wanting to buy one as well huh?

that price is crazy high just crazy it probably flows just a little better then a flowmaster to.

Oh it definitely flows better now. I noticed a difference in power on the way home after the install. It revs quicker too.

That is a pretty cool setup. I was wondering, if you car still had dual cats, would it be a direct bolt in or would an exhaust shop have to add some pipe. I've been thinking about possibly getting GMMG or Flowmaster American Thunder for my 92 GTA.

Dual cats...now that is an interesting question. My car came originally with the single cat. Probably would have to fab up something for the dual to fit.

thanks for posting this always up for info on the gmmg any pics on what you did to make the i-pipe reach the cat? I thought some had to be trimmed of the i-pipe not be added with the gmmg, but I could be wrong I too have been drooling over this exhaust for years now almost have enough to buy it lol

I think it's some years on the 4th gens that need to have the intermediate pipe cut. I can take some pictures of the cat/Flow/GMMG connection next time I've got the car in the pit.

First off, I must comment on your running shoes. They are nice, but I noticed that you pronate I tad. Maybe next time get a more stable shoe? Next, I had to laugh. Another skinny white kid owns a GTA. Gord, I thought you were from "The Dominican Republic"? . I guess you lyed since you told me you were Tony Fernandez's cousin.

Gord that car doesnt sound bad all. I must admit however, the tpis look somewhat cheap. They dont compare to the B&B tips. The lipped edge isnt thick enough. I am sure you agree. Sound wise, It doesnt sound bad. I think it would sound alot better with a mild cam in it.

I know you love yourr car more then your gf, but I will say this is quite the writeup. However, $1500? Are you nutz? You could of bought a set of AFR 180CC heads, and kept the stock exhaust. Just giving you a hard time, like you do with me.

BTW, Is that rust on the floorboards? Everyone knows your plate, and can figure out where you live. Your slipping.

Goodjob Gord. The main thing is that you are happy my friend. We will talk soon I am sure. I can hear my phone ringing. It sounds good!

Not to pop your bubble or anything but......

It's too bad you can't see just how small those chambered pipes are inside.

I'd bet money the FlowMaster flows more.

I was thinking the same thing, but you said it first.

sounds good, but wow... that price is hard to justify!

great post! looks and sounds great Reid! i got my GMMG for the same reasons as you did, just tired of the sound of my flowmaster and the fact everyone has one. my set up is a little bit different than yours.....i have duel catco cats, flowmaster y, and hooker 2055's ceramic coated. ill have mine on by next friday

Don't worry about 88BlackZ-51's comments. He's illiterate. He has to use a Teddy Ruxpin speak and spell to type up a post. He's from up near Chernobyl, so he's a little on the side. I think Rick is a tad jealous because he bought a system that's crooked and drones worse than his old Flowmaster.

Ceramic 2055's are what I've been tossing around in my head. Of course they're over a thousand dollars by the time they get here. But like the GMMG, they're a nicely made product.

Take some video after it's all done. If you have a dB meter (I got a digital one from Radio Shack. Think it was $60) that would be neat too.

Great post!

Damn that sound is pretty good and I kind of like those tips oddly enough lol

BTW Gord the car looks beautiful

now that was funny.Teddy ruxpin,how old is that.Car sounds sweet,but for that money I could have bought some serious hp or most of a paint job or a tremac anywayto each his own

Probably worth the money for the looks alone, regardless of how it flows and sounds. Nice car!!!

well i have my gmmg on and i must say im surprised, its not that much louder than my FM. at 55 its very tame, but when you step on it is when it screams. i purchased this cause i wanted a better sound, i wanted somthing different. i didnt want my car sounding like an ugly truck
is it worth $850....no am i happy....yes

Bullitooth, I find it surprising that you think this is a tame setup. Maybe the dual cats make it that much quieter than the single cat version I have? Then again your headers have gotta be making this thing loud as hell.

55 mph it's not too bad. Gets a bit too loud once you're past 75 mph though.

Video, video!!!

lol @ complaining on the price, yet buying the $150 extra tips lol.

Im glad you got it, it sounds awesome! I've definitely got more looks and comments now that I got the GMMG exhaust, then I ever have. I like the attention whore factor Replace the Stuper Ram with a Miniram too

Keep new vids coming if you got em!

I wonder how much louder it would be with headers and without a cat....

While I don't have a GMMG exhaust I can say this: I called Steve there (I think that was his name) and he was one of the main guys there. I wanted to know if he'd recommend his setup for my car (read my sig for the specs) and he was very honest and said no. That right there was dissapointing from the point I've always been VERY impressed with the exhaust sound and he was not recommending it. He actually recommended my second choice of a 4" mufflex system. For a guy to be honest like that and actually recommend a competitor told me alot about him and his company. If I ever have another car or application to use a GMMG setup I would.

Those arent brass. They're likely steel, with a zinc chromate plating/coating/wash.

Sounds pretty good. No drone? Gotta love that.

Technically they were $135 tips. The GP prices were $600 and $735 usd.

BulliTooth, when you said you got exhaust hangers with your package, was that both the passenger side box/rubber insert and the driver side SLP type thing that I have? I didn't get either!

Cad plating.

No Way. The Flowmaster flows worse than the stock LS1 catback. And GMMG puts these things on their project cars making well over 500 whp. Magnaflow out flows the FM by like 10% and it is outflowed significantly by the GMMG. I don't have exact figures as to how much these flow but if the GMMG did not outflow the FM then GMMG would be using FM catbacks on their cars. Matt Murphy has never put forth anything but the best to his customers. Hell there are alot of name brand exhausts out there, and they run their own over all of them, and it's not because it bares the GMMG name, but because it's the best.

And the number 1 reason I will be running a GMMG on my third gen:
It's Unique and they sound and look so damn good.

-Kevin

I recently scored a barely used GMMG set-up for $450. I prompty took off my custom 4 inch catback and installed the GMMG. My car went from sounding "nice" to sounding "mean as hell". This is on a stock crate LS1 motor in my IROC with long tubes and no cats. Can't beat the sound of a GMMG on a LS motor....especially when you flirt with the rev limiter at 6300rpm.

Funny thing is that I participated in a burn-out contest last weekend and heard from a few people that my car was the best sounding of the bunch.

That too.

Decided to do some outdoor testing to see if the police will bother me with this.

Car idling in park, outside, fully warmed up, closed loop. Decibel reader at waist level.

5 ft away: 92 dbC or 77 dbA
10 ft away: 88 dbC

Local rules dictate that gas powered cars should be no louder than 83dbA when measured at an inspection shop. Adding headers, I'd be juuuuust pushing it. As is now, I shouldn't have any concern.

Another great write up Gordy.

You got a Beautiful GTA!! I love that sunset pic. The tips are a nice touc h...but its a pricey setup IMO. On my TA I no longer have a Cat, so I assume it would be louder. Sound decent....cant wait to break it in I bet =) The hangars are well made. Can you get those seperately you know of?

Thanx for the review!,I also have a black 89 GTA and was wondering how the gmmg system would sound and look. thats excellent sounds like a vette!

For any random point of information:

GMMG Chambered Mufflers are a straight through design, they're true to the diameter of the ends of each pipe, and slightly wider throughout the tube for the crimps in the system. There is no packing inside, only a small set of flat baffles that bounce the exhaust into the crimps to give it the excellent sound. There is nothing to restrict flow in them.

the dimensions of his oval tips are 10.5" long, 6.5" wide, 2.75" tall, 2.5" ID

token LS1 member with GMMG checking in.

It's been a long time since I've updated this thread.

I phoned up GMMG last year and had them send me out the extra muffler hangers. So I got another set of the driver side hangers/rubber in the pictures posted above. Also got a new passenger side hanger. The passenger one is the same as stock. Just newer looking. I got them for no cost.

But why am I posting this? Because I found some old videos that were on my old computer. These are 3 years old. Taken before I got the Trans Go put in. (I'd forgotten how the car used to shift back then)

Turning off the highway.....Had to slow down after shifting into 2nd. (That corner is uphill and banked away from you. Can't really tell from video)



Fooling around at night.



The night shot, you can hear the original Gatorbacks make more of a sliding sound than a burning rubber sound. What can I say? They were 19 years old. I replaced them soon after these videos were made.

I have to admit, after 3 years of having the exhaust on there, I'm still lovin' it.

nice vids. ya after 3 years with gmmg i still love the way my car sounds.

drool can't wait till mine comes in......probably gonna be awhile pretty much impossible to get currently stock is out everywhere, and gmmg shop is pretty much shut down

Oh Gordie!


So did u want to buy some AFR's?

If only you had an LPE 219/219 and some matching rockers to sell with that.

just to add to the GMMG thread, if you guys havent heard my car since last year here is a sound clip with my new motor

http://www.youtube.com/watch?v=5cE1gOF7iLo

can u post the dyno sheet?

i love GmmG exhaust. they're definately on my shopping list but gonna be a while till i got the cash for them plenty of things i need done before hand..
=
Running dynomax catbacks right now w/ a hollowed converter(p.o. did both)

hey what hanger did you use to mount up the passenger side?

None needed. It slides right into the stock passenger side hanger.

this hanger isn't new? because mine looks nothing like that, and I currently have a fourth gen exhaust on my car, and when I took of my stock one I just slid the new one on my current one is basically a L shaped metal attached to over the axel and it slides into a rubber square hanger hmmmmm interesting

Where can i get a gmmg exhaust? Are they still made. I want one.