I finally finished my turbo-back exhaust for my 335is. I drove the car for a week with the an upgraded cat-back exhaust but stock downpipes. It was a nice upgrade from stock, but I knew it wasn't where I would leave off (had the downpipes sitting in the garage), so I didn't get too worked up about it. With not a whole lot going on this weekend, other than tornado warnings, I spent the morning in the garage and got the downpipes on.
Install was a moderate level. If you approach with a game plan and patience it is not bad. Just be prepared for about 3 hours of work. My only real struggle was getting the new v-clamps around the upper downpipe and turbo. That took me a very frustrating 30 minutes to monkey with. The lower downpipe had no issues. After that, it was a breeze.
After going for a drive, I have to admit that these things are game changers. The seat-of-my-pants dyno feels a major increase in responsiveness and power. I was actually surprised on how noticeable it was. Granted the roads were wet, but I've never so easily broken the tires free. Then add the sound... changes to car entirely. I'm going to be in trouble with speeding now.