as per...
DynoTech Research - motorcycle and snowmobile dyno testing facility
the dynoport Y-pipe on dynotech research gained about 2hp peak and 4hp in the midrange
Thats from another site where the poster had access to the report. Can you honestly say you would notice 2hp peak difference on a pull? Now you start adding up other gains, sure, I can see the benefit, but thats a big cost for a few HP - $100 per 1 HP.