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Discussion Starter · #1 ·
I picked up these axle backs second hand a few months back. Nobody really seemed to know where they came from (seller wasn’t sure either) so I’ve started calling them the “mystery mufflers”. This past weekend I installed them on my 2014 GT and made a video of the install and a sound comparison between these and my Roush axle backs.

I did some searching and they bear slight resemblance to the flow master outlaws and the American Muscle SR performance axle backs but not close enough to either to be a confirmed match IMO.

Anyways, here’s the video. Let me know what you think or if you have any theories. Thanks.

 

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FM got a contract a few years ago to build exhaust mufflers for DoD.... that looks like them....ie "glasspacks/resonators"
 

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Those two in the video sound so similar. I wonder if they drone.
 

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Discussion Starter · #4 · (Edited)
FM got a contract a few years ago to build exhaust mufflers for DoD.... that looks like them....ie "glasspacks/resonators"
Whoah, interesting. Never heard that before. Got any links?

Those two in the video sound so similar. I wonder if they drone.
I thought they sounded very similar at idle and at low speeds but that's where the similarities end. Once you get above 20 mph, the differences are very apparent. The mystery mufflers definitely drone and don't have the upside of the snap/crackle/pop the Roushes have. I didn't figure that out until I finally got it out on the highway at higher, cruising speeds....I got tired of it after a few days. This weekend I actually put my stock mufflers back on for the first time in almost six years. I can't believe how quiet the car is driving around. It's really making me lean towards trying to sell both the Roush and mystery mufflers and then buy the GT500 ABs.

 

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I have Corsa Touring Mufflers and X-Pipe on my 2013 GT. I wanted a smoother sound and no drone. It is louder than stock but not as loud as other options. Some people might find them on the quieter side. The Sports or Extremes would be better for them. If I were to buy again, I may consider the Sports.

For comparison, I'm not sure where on the scale my 2001 Firebird LS1 is (since Corsa only made one setup for it), but its not much louder than stock at idle or part throttle, but screams if you punch it. That is how I like it. Non-obnoxious driving around normal and loud when you put your foot down. Some people just prefer loud all the time, but not me.
 

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Whoah, interesting. Never heard that before. Got any links?
FM had PR in just about every car mag a few years ago..... nothing that impressed myself really. Personally, I run Allied resonators on everything that I have had for 30+ years...… and my family has as well...so that may just add up to 50- years :grin:…. They come in just about any diameter you could want and length's run from 10" to 38" IIRR...I typically get 15-17 years out of a set. No drone, well insulated, lots of nice deep rumble on accel/deccel.
 

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Discussion Starter · #7 ·
I have Corsa Touring Mufflers and X-Pipe on my 2013 GT. I wanted a smoother sound and no drone. It is louder than stock but not as loud as other options. Some people might find them on the quieter side. The Sports or Extremes would be better for them. If I were to buy again, I may consider the Sports.

For comparison, I'm not sure where on the scale my 2001 Firebird LS1 is (since Corsa only made one setup for it), but its not much louder than stock at idle or part throttle, but screams if you punch it. That is how I like it. Non-obnoxious driving around normal and loud when you put your foot down. Some people just prefer loud all the time, but not me.
I love the look of the Corsa (and the Borla) but couldn't justify spending that type of money on mufflers at the moment.

I had a 1998 TransAm waaay back in the day. Long tube, off-road Y pipe, and SLP loudmouth. It was absolutely bananas, even after I had a resonator put in to tone it down.
 

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. . . . . The mystery mufflers definitely drone and don't have the upside of the snap/crackle/pop the Roushes have. I didn't figure that out until I finally got it out on the highway at higher, cruising speeds....I got tired of it after a few days. This weekend I actually put my stock mufflers back on for the first time in almost six years. I can't believe how quiet the car is driving around. It's really making me lean towards trying to sell both the Roush and mystery mufflers and then buy the GT500 ABs.
More often than not, the AB's I've tried resemble me after bean night. I eventually installed the GT500 AB and haven't messed with them since. Nice tone, no drone, not annoying, and they don't sound like the day after bean night.
 

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The mystery mufflers definitely drone and don't have the upside of the snap/crackle/pop
If you believe snap crackle and pop is an upside to a mustang sound then maybe I shouldn't even respond.
But what the f¥€k, it's the World Wide Web right?!?!
In my humble opinion, the best sounding modern mustang motors are the fox body's 5.0s. I honestly believe they started sounding tamer as they progressed from there.
The early 4.6s sound great with the right set up likewise with the 05-09s.
But the Coyotes are a different beast. Once again, in my humble opinion, you can't replicate or even get close to that classic hotrod sound with the modern 5.0.
Any straight through or resemblance there of, will always make me cringe with embarrassment.
Don't get me wrong. I could buy a newer 5.0 any day. Just not my style.
 

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If you believe snap crackle and pop is an upside to a mustang sound then maybe I shouldn't even respond.
But what the f¥€k, it's the World Wide Web right?!?!
In my humble opinion, the best sounding modern mustang motors are the fox body's 5.0s. I honestly believe they started sounding tamer as they progressed from there.
The early 4.6s sound great with the right set up likewise with the 05-09s.
But the Coyotes are a different beast. Once again, in my humble opinion, you can't replicate or even get close to that classic hotrod sound with the modern 5.0.
Any straight through or resemblance there of, will always make me cringe with embarrassment.
Don't get me wrong. I could buy a newer 5.0 any day. Just not my style.
IMHO the Flat Head V8 ford firing order sounds the worce out of all the Ford V8's, The Coyote 5.0 shares it and the only reason I think it doesn't sound as bad is the Flat Head share the 2 center ports. The louder they are the crappier they sound.
 

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I have the 11 - 12 GT500 Axle backs on my 2013 and they are GREAT! My neighbors don't think highly of them, but my wife loves them and that's the only thing that counts:smile:
 

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Discussion Starter · #12 ·
If you believe snap crackle and pop is an upside to a mustang sound then maybe I shouldn't even respond.
But what the f¥€k, it's the World Wide Web right?!?!
In my humble opinion, the best sounding modern mustang motors are the fox body's 5.0s. I honestly believe they started sounding tamer as they progressed from there.
The early 4.6s sound great with the right set up likewise with the 05-09s.
But the Coyotes are a different beast. Once again, in my humble opinion, you can't replicate or even get close to that classic hotrod sound with the modern 5.0.
Any straight through or resemblance there of, will always make me cringe with embarrassment.
Don't get me wrong. I could buy a newer 5.0 any day. Just not my style.
I love the way the Roush sounds and have received countless compliments over the years from random people....to each their own on the snap/crackle/pop.

I have a Fox Body as well and personally love the way they sound but the drone I've been getting from the flowmasters has also been driving me crazy. I agree the push rod 5.0 is one of the best sounding cars...but definitely think an argument can be made for the 4.6 2V. I can't say I've heard a lot of the earlier versions but a close friend of mine had a 2002 and with headers, full exhaust w/ Mac mufflers, that thing sounded amazing.
 
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Discussion Starter · #13 ·
I have the 11 - 12 GT500 Axle backs on my 2013 and they are GREAT! My neighbors don't think highly of them, but my wife loves them and that's the only thing that counts:smile:
I can't imagine my neighbors have enjoyed the Roush ABs so maybe they'd appreciate the GT500 ABs being slightly quieter. :)
 

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Another vote for the GT500 AB ...
 

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It is anything but quiet. The headers add a lot of personality to the exhaust system.. It's hard to exercise the pony these days given all those restrictions. I warm the car up in the garage and then drive to the access road to our community. It is about a one mile stretch between my community and a main intersection. I slowly wind it up in first gear to around 6700 RPM and shift into second and do the same thing... My neighbors know when I'm on the road, trust me... I love it...
 
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