I did the airbox mod and it seems to make a small difference on the butt dyno. It could have all been in my head though. I feel unless you start putting throttle bodies, a cam, longtubes, etc., an aftermarket intake will only have marginal gains.
Mufflex DOD18M & Custom Intake tube w/air box mox
Diablo Intune DCX with Hemifever Tuning
Longtubes coming soon...
RIPP supercharger coming soon...