I was going to add this to b-stevens GMMG thread but it got kinda long...sorry man.

Here is my short evaluation of The GMMG Chambered Exhaust System:

I bought my GMMG chambered exhaust for $500 used from a Texan LS1 owner. I got my it installed and custom fitted a few weeks before I put my car in for winter. My friend's father Dale used to run his own body shop and now just does work on the side for friends, so he helped me install it. The I-Pipe I recieved from the previous owner was all fugged up (mutiple poor welds), so we tossed it and he just welded the assembly on from just after where the I-Pipe curves to make it over the axle. I figure minimal loss using the stock pipe since it is stainless steel and only a 1/4 smaller diamter anyways. He fabricated the new hangers from the ones we cut off the stock exhaust, since the LS1 hangers do not fit correctly. All said and done he just pried the thing to get the tips even and poof, a badass flowing and sounding catback. GMMG offered to sell me a LS1 to LT1 conversion kit for <$20. They also offered to sell me an I-Pipe, but as it turned out, I needed neither.

So, now my car has attitude, how about performance? HELL YEA performance!!! I felt....and yes, I do have a detailed working central nervous system, as most humans do, that allows my body to feel changes in my environment, so don't give me any bullpucky about not being able to feel a gain...anyways...I felt a very noticable differnce in power through all rpm's. The bowtie beast just pulled harded whenever pressure was applied to the gas pedal. I was quoted a 12-16 rwhp gain estimate from a GMMG techie with my otherwise stock platform and I definately felt it. He also noted that in one instance a GMMG owner tried using a cut-out with the catback on a "drag utilized modded big-block" and got decimal dyno gains. Free flowing for damn sure, it basically uses hollow pipes with small dimples for a "muffler."

Now the sound of this catback...well it sounds good like hooker and borla....WRONG it sounds incredible many times better than others, a consitant deep rumble at idle and a mean commanding hellaish scream at "extreme acceleration." It keeps deep and mean tone all of the time. You cannot even fathom the greatness of this exhaust's sound unless you've hear it in person. I figured it would sound pretty good considering the clips I had heard, but in person, it is unreal, simply unsurpassed. The tone at driving RPM from 1500-3500 is perfect for crusing even on a highway, just a tap on the gas and the 350 roars to life.

Oh yea, and it looks sweet too, I have the oval tips which are unique and really compliment the rear of the car nicely. The crossover piping is unique only to this system, very impressive. Great overall system made of quality materials and engineered flawlessly. I would highly recommend this catback to anyone who is interested an awesome exhaust tone and seat-of-the-pants performance. I'll have a website with pics up sometime soon. Yes I have video clips with sound, none from my Z yet, but several from other LT1's and LS1's. Here is GMMG's site for more information, enjoy the custom cars as well as the chambered exhaust. http://www.gmmginc.net/

-Dustin-

 

Sweet man!

I have it on my LS1 and am debating whether or not to put it on the LT1 I'm going to be replacing my Grand Prix with during the summer. Just not sure if it is worth spending all that $$$ again since almost every exhaust sounds bada$$ on the LT1 motor IMO...

BTW, I'm going to get to hear b-stevens car w/ the GMMG & headers in person this upcoming weekend as long as the weather cooperates. I'll have to let you guys know what I think...

Nice review,

Mike

 

Nice to see another GMMG owner provide such positive feedback Other f-bodies owners look at me all the time w/envy wondering what exhaust I'm running... and the mustang guys are like . I also have the oval tips and the just look amazing under the bumper... kinda old school chevelle style but bigger

 

Heads/BIG CAM/FLP's GMMG........can you imagine what I am going to get to hear? Currently I have just the FLPs into GMMG and I can't imagine it sounding any better now......but with heads and cam I will be in heaven.......
Brian

 

"Currently I have just the FLPs into GMMG and I can't imagine it sounding any better now..."

I have FLP's and Borla...and I REALLY want to switch to the GMMG. How loud is your car with this setup? Did the exhaust bolt right up the the FLP y-pipe?

 

Hey sleeperZ96BT GMMG sounds sic with a cam trust me

 

How loud is it? Really freakin loud.....outside........inside you can hear it but it has NO drone and NO rasp and NO resonation, its perfect IMO. Conversations can be had at normal volume when cruising. Keep the cats in though, the GMMG misbehaves like a lot of exhausts do without cats. You'll pick up some rasp and drone, but it is UNBELIEVABLY loud..........

Yes, it bolted right up. Had to cut a lil off of the Ipipe since the FLP ypipe is a lil farther back than the stock one. Was easy though, 30 mins maybe to get it on with a lift.

Brian

 

Yes, I can only imagine the sound of such a great exhaust getting even better. As far as headers go, I have been severly torn between Longtubes and Midlengths of some sort. Of course I read the 8 page debate and still am having trouble making a final decision. I like the Mac Midlengths because the catalytic converter can be swapped in and out with relative ease. This would make it easy to get the sound I want when crusing with the cat, but still be able to yank the catalytic converter in favor of the off road pipe when at the track or other opportune times. Yet for where I am going with a Camshaft and possible Port and Polish within the next two summers, my gut tells me Longtubes. I plan to run a Comp Cams 503-224/230 or a custom grind like the 227/233. Price favors the Macs, as well as ease of install. Although I feel like I am selling myself short if I don't go fullbore and get Longtubes like I went fullbore with GMMG. Any insight fella's? And how did you like the review?

Indy, thanks for your original video and pics with the GMMG, that basically sold me on it.

I'd like to hear anyone's setup with headers and GMMG, even though I also know it sounds much better in person. Of course b-steven's setup interests me, as well with any Jet-Hot/Hooker GMMG owners.

2002LS1Z28...Wish I could hear it...

Thanks for the posts guys and Melissa.

-Dustin-

 

What do you think guys, will I be able to make Mike jealous tomorrow? I absolutely love the sound of my car now and I actually prefer the look of the slashcut tips over the stock rectangle tips.

I think Mike might be as excited to hear my car as I originally was to hear his.

 

IMO, don't waste money on midlengths, get the LT's. FLP's are a 10 minute cat/OR pipe swap also............I have been more than happy with my set. Plus I can vouch for the kick assness of the FLP/GMMG (w/cats). I will try and get some sound online before and after cam..........
Brian

 

Yea its a nice system, just WAY overpriced for a catback

 

I've had mine since it was first available, originally called Braxxton. It's been my most enjoyable mod.

 

Great review. I'm trying to decide on what kind of headers to use myself. I'm going to keep the cat regardless. How much louder does adding headers to an already loud car make it? I don't need any more trouble with smokey.

 

Hey, sounds like a lot of positive for GMMG............. question.... I am about to put longtubes and ORY on my car. I have borla now, and my roomates car with this setup is SOOO RASPY. I don't want rasp in my exhaust. I was considering putting a new Proflo twister muffler in the I-pipe to cut some rasp out. BUT, with all this good talk about GMMG, I'm wondering how you header/ORY people like it.

 

Keep the cats in, you will be happier............GMMG is extremely loud and does pick up some rasp with no cats. No rasp with cats.
Brian