Switching from 2.5" glass-pack patriot side-pipes to 3" flowmaster 40's dropped 3 tenths from my 1/4mile E.T. (427++ BBC)

I don't know of any muffler out there that flows better...

However, they definitely are not quiet but I prefer the sound of the flowmasters to the glass packs I was running.

If you're looking for quiet at idle, though, you'll probably want to look elsewhere.

-Chris