[hcw5]

I believe this might have been addressed in another post somewhere because I remember seeing it, but I can't seem to find it now, so if someone knows what I'm talking about feel free to point me in the right direction. Anyways, what I remember seeing was the inside of a 335 muffler that had been cut open. There was some sort of material on the inside of the muffler that I guess would dampen the sound a bit. Does removing the material cause the sound to increase at all? I have a 435 muffler already that I'm going to put on my 328 and figured I could have it cut open when the shop installs it.

[lfepro.g]

From what I've seen from YouTube videos, even the people that full straight pipe their exhausts keep the packing inside

[Billfitz]

That material is probably fiberglass, and it only affects the higher frequencies. Lower frequencies are damped by the baffles in the muffler. This explains how:
https://auto.howstuffworks.com/muffler2.htm

[hcw5]

Originally Posted by Billfitz

That material is probably fiberglass, and it only affects the higher frequencies. Lower frequencies are damped by the baffles in the muffler. This explains how:
https://auto.howstuffworks.com/muffler2.htm

so a lack of fiberglass probably would not make a very noticeable difference?

[Fronttwelv]

Have the shop take out 50% of the packing and weld a pipe around the perforation pipe inside the muffler. This is what gave the best sound on the e90 335s.

[Billfitz]

Originally Posted by hcw5

so a lack of fiberglass probably would not make a very noticeable difference?

Not the way you want it to, assuming you're looking for a deeper, more throaty sound. You get that with 'glasspacks', which have no baffles and are stuffed with more fiberglass than standard mufflers.