I put on my GMMG this weekend. It only took me 2 hours in my garage/driveway by myself and searching for tools (I really need to clean this place up). I had high aspirations of removing the stock exhaust intact. However, when faced with thought of how much work was involved (and how accessible the SawZall was), I caved. One cut over the axle, an impact gun on the Y-pipe clamp (15mm), 13mm for the passenger side hanger and it was out. I had no trouble removing the stock exhaust. However, I couldn't get the GMMG in without removing the panhard rod brace. If the car had been on a lift, it might have been possible. But my 3 ton jack was at the limit of it's reach lifting the car as high as I did. But with the impact, I just zipped off the 3 15mm panhard brace bolts and the 18mm nut for the bolt on the other end. I also removed the two 7mm heat shield-to-panhard brace screws as well. This let the brace sit down on top of the panhard rod which gave me enough room to snake the assembly in there. It sure doesn't seem like a lot of room upon close inspection.

I got the standard tips with my setup. I wonder if the optional tips would change the sound at all. I have a set of stock tips that I'm going have a friend polish and put them on the GMMG. I think it'll look pretty good except for the fact that I have painted wheels instead of chrome. In any event, I'm happy with the sound and performance of it. I'll get some hp/tq numbers at the next dyno day. The car has a deep rumble to it that I really like. There's no rasp but that's probably due to the fact that I haven't put my ORY on yet. What amazed me is that it is much louder at part throttle and loaded conditions than it was before, HOWEVER it is only barely louder at idle and NO louder cruising in 6th than it was before. The interior is perfectly civil cruising at 75 in 6th. I love it.

So those are my impressions and experiences with it. I included the socket sizes in case anyone searches and wants to know.

 

Congrats! I love mine more after I put LTs and ORY

 

Congrats

 

Wait until you get headers, heads and cam

 

wait untill you install the ory the rasp will come.......

 

Sounds like the GMMG installed like my old Magnaflow setup, minus the panhard bar part.

I guess that I'll have to hear the infamous GMMG sound the next time we run into each other.

By then, I'll have the Sweet Thunders on my duals, so you can hear what they sound like.

 

GMMG is an excellent cat-back system, perhaps the best out there for performance AND sound. I now might have to part ways with mine because after cam/heads/headers/catted-y it's just too loud. Awesome sound, just too loud.

 

When I first installed my GMMG, the sound was PERFECT as far as I was concerned. After installing my TC, it borders on too loud at times - sometimes, especially when the car is cold and the windows are up, it'll make my ears buzz. When I have "mature" passengers in my car, (other than my wife) I have to feather the throttle so I can hear them talk, and not blow them away with the sound. It's funny - somedays it's perfect for me; other days I swear I'm going to ditch it and get a Hooker. But then just tonight, a gal outside the liquor store said, "man, I forgot how good those cars sound ..."

 

Sweet man, congrats!

 

Whats up Eric? Dont know if you remember me or not, I was the guy with the car in the sig that came down to get tuned by gomer. Glad to see you're making progress on the car. Hard to beat the GMMG. Very nice choice. Now get some headers to really set it off.

 

Hey Josh, sure I remember you. You came to the show for a little bit afterwards. Nice car. I like the GMMG, but I dunno about headers. Normally, I'd say they are one of the first mods one should do to an LS1 but I've got plans that would make them obsolete.

 

I follow. Nothing wrong with that.

 

nice write up, but exactly why I will pay the $75 to have mine installed....I used to do all the wrenching on my cars, but now that I'm old ....I just have more money then time and patience now-a-days......nice to let someone else lose the knuckle skins and get dirty....drive in. pay, drive out....clean and simple I will watch everything they do though.... and if it's not right......

 

Congrats Eric, whats the butt dyno tell ya? And i do want to hear it

 

Hey Roman, the PD (posterior dynomometer) says about 10 horse. The problem I'm having now is the rear wants to run out from underneath the car. By that, I mean I don't have the traction to hold what little I have. I can roll into first and mat the throttle and 'round about power peak, it will start scratching the tires over. Normally, that would be impressive, but with as little as I've got, it just means that my tires are waaaaaaaay past due for replacement.

 

I doubt you'll like an ORY through that GMMG...Unless you like the sound of nasty rasp and popping in the mid rpms. But why ruin the perfectly good and clean sound of this set-up?

BTW, the GMMG does sound very good (just like you described) behind stock manifolds & cats, but it sounds much meaner with some nice LT headers + highflow cats. The tone is a little deeper and full throttle is a LOT louder (more menacing)...

Mike