Sound and Fury:
You can check out the video ( normal quality or high quality) that Chad and I made. Chad did the camera work, and I did the driving "work". It was nice to see and hear my car in action from the outside, since normally no one has a chance at getting behind the wheel! For more information and pictures, check the exhaust upgrade explanation.
As the video mentions, the new exhaust is about 50% louder (+5 dB) at full throttle. The startup sound levels are slightly higher, perhaps 15-20%, but a lot lower tone. The character overall went from mostly engine valve whine with a higher pitched exhaust note to a lower base note with a bit of burbling after letting off the throttle. As with other systems, the 3000-4000rpm range has the most resonating sound, and I'll have to hunt down a pair of buzzes in the B-pillars due to the much lower frequency rumble. However, overall I like it a lot better than stock!
In terms of instrumented performance gains, I didn't expect any real change since it is just a muffler swap (the stock muffler isn't truly restrictive.) As you can see by this power comparison, the before-muffler and after-muffler HP readings are essentially two horsepower apart. However, when factoring in the changes in temperature (check the spreadsheets before and after) and what-not between the tests the readings are essentially identical. So we didn't get any faster, but I think it definitely looks and sounds better!