M240i with 200CPI DP and CBE exhaust from BCS here in the UK - valved system - valve closed at <part throttle and flow goes through rear muffler and out both LH and RH pipes. WOT valve opens to bypass muffler and flow exits RH pipe only...
Taken from this BabyBMW thread
http://www.babybmw.net/forum/viewtopic.php?f=74&t=95924