Both engines have 47/39 valves with a 1.72 head gasket. The B9 is a 93.4 bore 84 stroke making it a 3453cc. The B10 is a 92 bore with 86 stroke making it a 3430cc. The B9 makes 320nm where as the B10 312nm both at 4000.
For the B9, Alpina claims a 0-100 km/h time of 6,7 seconds and a top speed of 240 km/h. For the B10, Alpina claimed a 0-100 km/h time of 7,4 seconds and a top speed of 252 km/h.