Thanks for your thoughts. I'll go through your huge, 13 page thread when I get a chance... heh.
And FWIW, I had those ART Pipes on my HR Z.
Those are what I'm referring to. Well actually I had regular test pipes, then went to the ART Pipes to try to regain that lost low-end TQ. Didn't work. I needed a tune. Was in college and broke back then so tune was not in the cards at the time, unfortunately.