GMMG Guys ...
GMMG Guys ... Two Questions:
Got my GMMG on a month or two ago and then just recently a new custom y-pipe. I had it on for a couple weeks and now there's an almost deafening drone/backpressure kinda sound right at 2400rpm. Any higher and it goes away, any lower and it's fine. It kinda reminds me of when i had my LM on there ... Does yours do this?
Also, when i let off it from higher rpm, there's no 'cackle' or sputter from the back pressure of the exhaust, it just kinda drags back down the tach ...
Are these normal characteristics of a GMMG? They both just seem kinda odd to me. I checked ls1sounds, but there's no real clips of what i'm trying to listen for..
Got my GMMG on a month or two ago and then just recently a new custom y-pipe. I had it on for a couple weeks and now there's an almost deafening drone/backpressure kinda sound right at 2400rpm. Any higher and it goes away, any lower and it's fine. It kinda reminds me of when i had my LM on there ... Does yours do this?
Also, when i let off it from higher rpm, there's no 'cackle' or sputter from the back pressure of the exhaust, it just kinda drags back down the tach ...
Are these normal characteristics of a GMMG? They both just seem kinda odd to me. I checked ls1sounds, but there's no real clips of what i'm trying to listen for..
TECH Enthusiast
Joined: Dec 2003
Posts: 530
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Is your Y-Pipe catted? When I was researching for GMMG it was very evident that unless you had some type of backpressure, then the GMMG would sound very raspy. Alot of people ragged on me for not just running an open Y, but I have hi-flow cats and it works out perfectly.
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
I'm on stock manifolds, but FWIW, no drone here at those rpms; inf fact, that's where I cruise on the fwy - 2400-2500 rpm. But it's pretty loud in general when the car is cold and the windows are up. Not much cackle either - it'll usually give a good pop once when decelerating.
I don't have GMMG on my car, but I know that exhaust drone often depends on what headers you run (either just manifolds, midlengths, or longtubes), what type of crossover pipe you have (either Y, H or X pipe) and where the engine causes more resonation in the pipes. Every LS1 I've heard has a resonation at 2400-2500 rpms. I think thats the nature of the engine itself. Sounds like your setup shows that off quite well 
You could throw a bullet, magnaflow bullet, or borla xr1 in there and it would help to deaden that loud spot.
You could throw a bullet, magnaflow bullet, or borla xr1 in there and it would help to deaden that loud spot. 
Teching In
Joined: Apr 2005
Posts: 29
Likes: 0
From: WI
My exhaust is all stock except for the GMMG cat back. I get no drone at any RPM's. When I let off I do get a pop once in a great while, otherwise it drags down usually. I really love the way this thing sounds!!!
Originally Posted by LS1vazquez
Is your Y-Pipe catted? When I was researching for GMMG it was very evident that unless you had some type of backpressure, then the GMMG would sound very raspy. Alot of people ragged on me for not just running an open Y, but I have hi-flow cats and it works out perfectly.
Yep, I have a custom catted Y from mufflex.
Originally Posted by RM99Z
I don't have GMMG on my car, but I know that exhaust drone often depends on what headers you run (either just manifolds, midlengths, or longtubes), what type of crossover pipe you have (either Y, H or X pipe) and where the engine causes more resonation in the pipes. Every LS1 I've heard has a resonation at 2400-2500 rpms. I think thats the nature of the engine itself. Sounds like your setup shows that off quite well You could throw a bullet, magnaflow bullet, or borla xr1 in there and it would help to deaden that loud spot.
You could throw a bullet, magnaflow bullet, or borla xr1 in there and it would help to deaden that loud spot.I have pacesetters and I don't see exactly how a bullte muffler would fit anywhere on that setup?
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Originally Posted by KrazyDan
gmmg does have a little drone at around 2600 rpm. Once you get some headers and catted y, there will be zero.
But I have the same setup it looks like as KrazyDan does. I thought my GMMG was perfect with stock manifolds and cats, with longtubes and cats it's even better. No rasp or anything.
Originally Posted by KrazyDan
gmmg does have a little drone at around 2600 rpm. Once you get some headers and catted y, there will be zero.
Once I get some headers and catted y??? (sig....cough .... sig ..... cough cough ....)
TECH Fanatic
Joined: Jan 2003
Posts: 1,415
Likes: 1
From: San Diego/Schertz,Texas
Originally Posted by Xtreme57
Once I get some headers and catted y??? (sig....cough .... sig ..... cough cough ....)
DOH! Ok , im dumb. Sorry.I dont know where its coming from then, cause I have zero. Sometimes Ill get a little backfire after letting off the gas, but never drone or rasp.
Originally Posted by KrazyDan
DOH! Ok , im dumb. Sorry.I dont know where its coming from then, cause I have zero. Sometimes Ill get a little backfire after letting off the gas, but never drone or rasp.
****. i can't figure out what's going on with this car. maybe the config of the new y-pipe? would that have any bearing on the sound/performance of the cat back?
TECH Enthusiast
Joined: Sep 2003
Posts: 702
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From: Lakeland, Fl
you will get something about that rpms with your setup. When I went to LT's and custom Y w/out cats it dropped down to about 2200 rpm's. At highway speeds it should not be a problem for you. You could add a small bullet if it really bothers you.
