Just had a knock off Flowmaster type removed. I was getting a vibrating/rattling sound during deceleration. Diagnosed as a flap or whatever was inside the muffler had broke loose.
I chose to try a Magnaflow muffler is place of.
Sound and Tone check:
Flowmaster (knock off) was loud as hell and was raspy nasty loud upon heavy acceleration.
Magnaflow is loud but with a smoother non raspy tone. Brown sound if you will

I have test pipes and racing Y pipe and stock headers.

The Magnaflow seems to allow more power, better flow, less irritating rasp. More Import sound like... meaner.
Flowmaster may be better suited for V8 throaty sounding engines. Too much rasp on the Z.
The Magnaflow is definately a tonal/sound and performance upgrade.
Glad to see the tech toss the Flowmaster in the dumpster

 

Cant compare a knock off flowmaster to a legit magnaflow. They both need to be legit!

 

Well, it looks like I just made that comparison.

 

Touche' but to make a good comparison they both need to be legit.

 

Yeah ur right. I did ask my tech's opinion. I was ready to put a new Flowmaster on. They suggested I may still get that raspy tin can sound with an original Flowmaster. I opted for the Magnaflow, which is loud and full of tone, not that atomic, Bumblebee sound.
I love 'loud', but what I had was a bit too over the top.