nope, at least no one has ever been able to measure any. From my armchair philosophy, since we see a 10hp bump when going to smooth tubes with the stock airbox, the last thing I'd do is introduce a 'S' bend into my tubes with an aftermarket airbox. The K&N aftermarket box does this (the box, not just strapping two big cones to some metal intake tubes).
Take the rain baffle out of the stock box and then I don't think it gets much better.
Take the rain baffle out of the stock box and then I don't think it gets much better.