My experience, mostly acquired from my service dealer, is that if you open up the stock airbox (remove snorkel, UNI or K&N filter, maybe bellmouth) and get the best needle/jet arrangement - there is no need to remove the airbox.
From the dyno results I've gotten, I don't see any gain from removing the airbox. There are a lot of "freaked" bikes whose dyno results can't touch mine. Plus, I like the airbox and battery where they are.
