different engines...all Bandits, water and air-cooled, have the cam chain in the center of the engine. The Hayabusa has the cam chain on the side. I can only assume it was less expensive to adapt the machining of the original GSX-R/Bandit engine instead of making a Hayabusa variant. One reason also might have been to differentiate the B-King from the Bandit, since the B-King did have a Hayabusa-based engine.