My Strada has its airbox opened in the same way as aka.eric's, and this increases induction roar a good deal. However, if you want the full effect you'll need to ditch the lid altogether, in the way it's done on the SP models. On these bikes, the air filter is held in place by a rectangular metal frame which tightly surrounds it, and which is itself secured by over-centre clips. Modified this way, the induction roar almost drowns the exhaust noise!!