ummmm...why do 3sgte's have different HP ratings Options

[Swifty]

Ive been researching the topic and have yet to come across a reason for the difference in the ST185 ratings, the USDM engine only pulls 200 HP and 200 lb/ft of torque, while the JDM versions of the same engine make between 221 and 231, im almost positive that the engines themselves are identical, same bore, stroke, CR...etc, so where does this mysterious power lie hidden. Could it just be the difference in the stock boost setting, are the turbos the same, what gives?
I'd like to get myself one of these babies, and im wondering if i get the USDM version if it would be an easy matter of freeing up the 21-31 HP in there,
this is only regarding the ST185 3SGTE, and not any other generation of the engine
Also if anybody knows any place that would sell the USDM engines here in Ontario (maybe even Quebec), cuz id much rather not end up having to buy the whole car (im on a freakin' buget, university starts in the fall)