if you are a street rider unless you plan to map, I would recommend keeping your flapper intact and buying a premodded box (they are quite abundant).....the "box mod" does kill your low down torque on a stock or slightly modded bike. It makes the bike a bit louder under hard throttle, but that isn't a guarantee of power. YEs if you are a racer or do a lot of top speed runs the mod can help, but I wouldn't do it again on a street bike unless it has full exhaust and is mapped.