Finally got around to installing my 335is mufflers. They definitely sound a lot deeper, louder, and more burbly than the stock mufflers! Very similar to the Performance Exhaust. I have the butterfly valve open btw.
Here's a cold start video with some low revs at the end:
https://www.youtube.com/watch?v=suEu...DZD2YN0zXuiFTw
EDIT: Here's a sound clip of my car revving with downpipes! I'll post a cold start video sometime over the weekend.
https://www.youtube.com/watch?v=0GcyNyXSFiw