Just drilling out the airbox ? Do you mean opening up the bottom? I did that for my 08 America and dropped in a K & N filter and it made a difference, however, with additional mods I think you would want to eliminate the air box and go with pod filters for a much better improvement. I did my own air box elimination, and I am not a mechanic. It was a straight forward job and adding pod filters makes a difference.
Since you've been happy with your bike for 5 years you probably don't need to go too extreme to add additional power. Removing the air box and adding pods, going with billet intakes, change to a stage 2 igniter and drop in a set of 813 cams, all for probably around $1,000 and you'll have 10 - 15 hp more than stock.
08 America, A/I &, Calif emissions "stuff" gone, air box removed & battery relocated, billet intakes, UNI Pods, 145 mains, 42 pilots, Stage 2 igniter, intminators, 813 cams, Progressive 412's, modified seat.
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