I have all the components to put together a mousse can muffler. I am wondering what the purpouse is of the aluminum 6" pipe inside of the mousse can does, and if I can do away with.

I got the know how from this web site
[link=http://www.spadtothebone.com/SPAD/Mufflers/Irvine_1/irvine_1.html]Mousse Can Muffler[/link]
but it does not say as to what the purpouse is or if I can do with out.

thank you.