HaHaHa, STORY TIME!
I bought the Calmini header for the Gnewt - it was the first mod I did. But I didn't get it installed before I went to EJS in 2002, so I took it along, and installed it at my tent site, at Slickrock Campground.
Well, you know how it is. You put the header on, and before you bolt up the Cat, you just gotta turn it over, to see what it sounds like, with open pipes. I was surprised that it wasn't a lot louder! Somebody described it as a pi$$ed-off bumblebee.
I have the calmini header on BOTH my Sidekicks - it's a great boost in power, performance, AND mileage.