From BMWCar April 2013:
"So, Alpina did the only logical thing, and asked BMW to cast the N55s destined for the F30 B3 differently in order to allow for Alpina to be able to accommodate a twin-turbo configuration. Then there was the small matter of the bespoke intake system, subsequent piping, cooling, Alpina-specific NGK spark plugs and forged-steel crankshaft which has resulted in pretty much a bespoke engine made just for this car."
"while the exhaust system comes from Akrapovic, weighs 7.5kg less than the E9x B3 item, and features an electronically-controlled variable valve that ensures the car is civilised when it needs to be but when pressing on, or when Sport mode is activated, it opens up"
"bespoke springs from Eibach, allowing you to bring the most out of the chassis, which has been further enhanced by the addition of a front strut brace, positioned right at the front of the engine bay, in order to counteract the F30's inherently soft front end."
Chart comparing F30 B3 Bi-Turbo power figures versus those of the E90 B3 S Bi-Turbo