I have a good friend who has a 2004 Caddy DTS with the 4.6 v8. He loves the sound
of my 05 GXP. So; he goes to his local Pontiac dealer parts dept. and they can't
find the mufflers in their system. I even give my buddy my VIN # so they can pull-up
my car to order replacement mufflers but no luck. At that point "Mr. Goodstench" at
the parts counter didn't want to be bothered any more with my friend, and blew
him off, which isn't a good thing to do,as he is 6'4 and 250. Anyway, does anyone
have any suggestions how to get the part #* of the GXP mufflers? I think I remember
reading that they were made by Corsa but I'm not sure. And In the future, If I have to
replace my mufflers; it would be nice to know that I can get the factory replacements.

from the parts list I was looking at, it appears you can't order the mufflers/tips or anything separate. the part number for the entire cat-back system is 25763175

the part number for the 00+ SLE/SSEi mufflers are (L-R) 25714639-8... how different from the GXP mufflers? I dont know.

I thought the GXP mufflers were made by BOSAL, just as the rest of the Bonnevilles and other higher-end GM vehicles.

They are made by Bosal. The GXP concept has Corsa'* but when it hit production, Bosal'* were used.

Is anything known about the flow capabilities of these Bosal mufflers? I know that the general consensus is that stock Bonneville exhaust systems don’t leave any significant room for improvement at near stock power levels, but I’m interested in any other information on these mufflers.

What’* interesting to me is that my GXP sounds awesome inside the car. Yet when I’ve been outside the car when someone else was driving, the exhaust sounded kind of crappy to me, and much different than how it sounds inside the car.

The mufflers are large, and easily outflow the single pipe coming out of the single cat. It would take alot of mods and dual exhaust to even consider that the mufflers would be holding You back.

I have no idea what the internal structure of the stock GXP'* muffler is, but 'large' does not necessarily = increased flow (even if the inlet/outlet pipe diameter is large). I'm not trying to start an argument....just food for thought.
I would 'assume' by all that I've read and heard that they flow very well. I gained quite a bit on my '97GTP by removing restrictions from the headers all the way back ....no cat, edelbrock RPM cans, etc.....enough to run 106mph in the 1/4
I would be interested in actual flow #'* as well.....if anyone knows the Bosal part # etc. FYI, I like the sound of the exhaust....it'* one of the first things people comment on for me...

my exhaust sounds great when the engine is cold, but after it gets warmed up you cant hear it (inside the cabin anyway)

I love the sound of my stock system outside the car but I still want it just a little bit louder. I am still kicking around the idea of new mufflers.

As stated by blacksedan, the outside of the muffler is not relevant, only the internal pipe diameter and design. If that is known or has been checked out, then that is the type of information I am interested in. It may very well be true that there is no significant horsepower lost to the mufflers on a stock GXP. I just haven't seen any testing or other data that specifically supports that, so I'm not ready to completely write that off just yet.

Also, I'd like to know if the GXP mufflers are the same part# as the SSEi mufflers. I do believe that the SSEi has been tested, and with stock or near stock power levels, there was no significant gain by switching to aftermarket mufflers.