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Discussion Starter #1 (Edited)
I feel like I've been chasing my tail the last few days while trying to find details as to the innards of the factory G8 GT axleback and how it compares to the highly sought after GXP axleback assembly. I thought finding GT mufflers that had been cut open was a trick, but finding a set of GXP mufflers spread eagle was the true challenge. Never the less, G8Board and Google prevailed....

G8 V6 Axleback
I was unable to find any verification as such, however I believe this assembly to be of identical internal construction to the G8 GT axleback. Anyone with contradictory information, please feel free to provide it. I did not investigate this further as it was not in my interest nor did I feel it would be in the interest of anyone else.

-Single outlet to a single chrome tip
**Additional details will be outlined under G8GT Axleback**

G8 GT Axleback

Acoustic design shared with the G8 V6 and Commodore SV6. (Unconfirmed: May also be used on V8 Calais, Omega & Statesman models)

-Single outlet split into two chrome tips
-Double-wall stainless body construction
-Stainless inlet and outlet piping
-Mild steel interior tubing
-Stamped 'dot-matrix' perforations
-Stainless chamber walls
-Three chamber construction
-Fiberglass packed first and third chambers

Illustrated (Requires updating for accuracy)


Dissected

Flow detail
-Air enters the inlet piping.
-Inlet feeds first interior tube.
-First interior tube is perforated, venting to chambers one and two.
-Chamber walls are perforated, allowing gas exchange between chambers.
-Second interior tube feeds from chamber two.
-Second interior tube feeds outlet piping.
-Air exits outlet piping.


G8 GXP Axleback

Acoustic design shared with the Commodore SS, SSV & Non-BiModal-equipped HSV models.*

-Dual outlet split into two polished stainless tips
-Double-wall stainless body construction
-Stainless interior tubing
-Stamped 'louvered' perforations
-Stainless chamber walls
-Stainless inlet and outlet piping
-Three chamber construction
-Fiberglass packed second chamber
*HSV models typically have unique tip configurations

Illustrated


Dissected


Flow detail
-Air enters the inlet piping
-Inlet feeds first interior tube
-First interior tube is perforated, venting to chamber two.
-First interior tube dumps into chamber three.
-Second interior tube feeds from chamber three
-Second interior tube is perforated, venting into chamber two.
-Second interior tube dumps into chamber one.
-Third interior tube feeds from chamber one.
-Third interior tube splits into two outlet pipes
-Air exits outlet piping.

Conclusion
What I take from all of this is that the V6/GT exhaust is a restrictive design, but that it does not hinder the car even at increased power levels. Changing this will net a couple WHP but is primarily done for the sake of making the car sound 'awesome'. We all want awesome at the end of the day. The GXP exhaust is nothing exotic and is standard issue on the V8 Commodores. It mirrors the construction of most quality aftermarket turbo-style mufflers. Most aftermarket ones will benefit from improved flow due to larger piping but again the difference in power is minimal. This design explains why they are slightly more aggressive sounding than the V6/GT mufflers since they have a plumbed path all the way through as opposed to fighting a vented barrier wall.

I've seen the question asked a LOT of times but rarely answered so hopefully this helps those interested... if you feel that any part of the above information is inaccurate, please contact me by PM. I'll make adjustments as additional information is provided. I cannot take credit for the dissection images, they were found via Google Image search and then I added corresponding illustrations to explain the most-basic flow characteristics.

I will likely overhaul this information in light of it being given 'sticky status'. My illustrations do not accurately indicate all potential air flow paths or differentiate between those that attenuate sound waves ONLY.

Thanks!
 

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very informative post - thanks & good job......
 

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FWIW, many, many exhaust threads between the two boards as I'm sure your googling showed you.

For the GT, from a flow restriction POV, it's the cats. Those are where you look first. The mufflers have been showed to be good for almost 500rwhp before they become a issue worth chasing (see other board).

For those who dare to read, here are three articles that allow you to see beyond the internet/salesman propaganda and make educated decision(s).

Exhaust demystified

LS1 header testing

Engine coatings - worth it?
 

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You need to make a correction to the GT muffler. There is no flow in the third chamber. All the flow comes in the perforated inlet tube. some exhaust is absorbed in the first chamber. The rest is forced to flow out of the perforations is the second chamber.The tube dead ends at the third chamber. Sound is further absorbed by the through the walls of the perforated chambers 1 & 3. Flow then goes out the "J" tube to the outlet.

The GXP is a typical 3 tube turbo style muffler. The difference is the dual outlets. the GXP only has fiberglass packed in the centre chamber. Not the ends like the GT.
This dynomax turbo is the same design. Just swap the centre and outlet tubes. It is great to actually see the guts of the GXP muffler. Kind of what I expected it to be from the sound. I went with the Stainless Works Turbo chambered mufflers.
 

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I agree a very informative post. You managed to answer quite a few of my, well does this thing right here do paw questions. Sweet.

On a different note, please look more into the construction of the V6 axleback...
I did not investigate this further as it was not in my interest nor did I feel it would be in the interest of anyone else
... because I'm interested. I kid. I kid. Thanks for even including us in your thread.
 

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Discussion Starter #8
You need to make a correction to the GT muffler. There is no flow in the third chamber. All the flow comes in the perforated inlet tube. some exhaust is absorbed in the first chamber. The rest is forced to flow out of the perforations is the second chamber.The tube dead ends at the third chamber. Sound is further absorbed by the through the walls of the perforated chambers 1 & 3. Flow then goes out the "J" tube to the outlet.
You are correct -- I'll update my illustration and notes. It should be noted that the 'J tube' in the factory muffler is not a Helmholtz resonance chamber like that found on the Solo exhaust systems; it is merely a J-shaped outlet pipe.
 

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Car RamRod
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Right, but this J-shaped outlet pipe is responsible for the drone cancellation in the factory GT muffs. Even modded, as long as the J-pipe is left tied into the outlet of the factory muffler, it will cancel drone.
Also, the GT factory pipes are 2 inch in the muffler, not 2.25.
 

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Re-opening this, as I could not find a related post. If need be, I'll start a new thread, just let me know.

This weekend after a few hard runs, I noted the fiberglass packing coming out one side of my tailpipes. Ended up pulling out over 5 feet. How much trouble am I in, any ideas of what I should do next?
 

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Re-opening this, as I could not find a related post. If need be, I'll start a new thread, just let me know.

This weekend after a few hard runs, I noted the fiberglass packing coming out one side of my tailpipes. Ended up pulling out over 5 feet. How much trouble am I in, any ideas of what I should do next?
The fiberglass is there for sound deadening. There is no real reason for it other than that and is usually a last resort for tuning if you can't use tubes to tune out certain frequencies or to bring the overall noise level down. It is rather expensive so we avoid it and it comes with other complications (manufacturing and durability). The durability issue is not of concern outside of China/3rd world. -Tier 1 OEM exhaust engineer
 

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Its Good To Be Tha King
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This weekend after a few hard runs, I noted the fiberglass packing coming out one side of my tailpipes. Ended up pulling out over 5 feet. How much trouble am I in, any ideas of what I should do next?
Warranty should cover it.
 

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Car RamRod
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Re-opening this, as I could not find a related post. If need be, I'll start a new thread, just let me know.

This weekend after a few hard runs, I noted the fiberglass packing coming out one side of my tailpipes. Ended up pulling out over 5 feet. How much trouble am I in, any ideas of what I should do next?
Sound deadening...and you will not notice a change in sound. I'd say no biggie. I pulled all of the packing out of mine. Still no change.
 

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Discussion Starter #16
I haven't forgotten about this sticky; I've just been too busy to sit down and work out some better diagrams and explainations.

Right, but this J-shaped outlet pipe is responsible for the drone cancellation in the factory GT muffs. Even modded, as long as the J-pipe is left tied into the outlet of the factory muffler, it will cancel drone.
Also, the GT factory pipes are 2 inch in the muffler, not 2.25.
It just happens to be a similar 'J' shape like the much-popularized Helmholtz chamber that SOLO uses on all of their systems, though it provides no resonance attenuation as the shape is not the attenuating factor but the volume (airspace). The OEM 'J' is an un-tuned section of pipe to ferry exhaust gases from the middle chamber of the muffler to the outside world. The rear-most chamber of the muffler does attenuate certain frequencies but the overall sound reduction capabilities of the stock exhaust system, especially the rear mufflers negates a majority of concerns.

Some (myself included) report 'No resonance' using the factory GT mufflers with headers, but this isn't entirely accurate. There is still some notable resonance at certain engine speed/load combinations, just far-less than most axle-back only systems emit and thus is judged lightly. This is simply because the parameters have changed from a stock car and the mufflers are no longer tuned to the rest of the system. The SOLO J-pipe is an adjustable 'catch-all' resonance chamber that can resolve most concerns across a wide range of configurations as is well-documented on these forums.
 

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Car RamRod
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I'm not sure I buy the internal J has no purpose. Consider why it is there. If not for attenuation of drone, they could have saved money by merely tying the tailpipe to the middle chamber with a single short pipe.
I have long since gotten rid of my internal muff pics, but I do understand that the internal J is shorter than the SOLO (or pre-solo in my case)J bends. What I do know is that I cut the hell out of the inlet pipe, such that it dumped into the middle chamber, and left the J outlet intact. There was no drone (with LTs and HF cats on 2.5 inch pipe), and very little change in tone at the outlet. I agree with your take on the SOLO...made for many situations.
 

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Its Good To Be Tha King
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I think everyone's B2B warranty is expired by now & it's not covered by any other warranty.
Late rebuttal....but I believe our exhaust system has a longer warranty than our powertrain. 10 years/150,000 mile coverage I believe.


edit....I could be wrong, google search isn't helping me out...
 

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Discussion Starter #19
I'm not sure I buy the internal J has no purpose. Consider why it is there. If not for attenuation of drone, they could have saved money by merely tying the tailpipe to the middle chamber with a single short pipe.
It forces the air to spend more time in the muffler, passing through two chambers instead of just one on the exit path. This reduces volume but would not target specific frequencies like a Helmholtz chamber.
 

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Late rebuttal....but I believe our exhaust system has a longer warranty than our powertrain. 10 years/150,000 mile coverage I believe.


edit....I could be wrong, google search isn't helping me out...
You're thinking of the 8yr/80k mile warranty on the Cat converter. (You know, the one that turns cats into dogs... ;) )
 
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