Don't, that will put too much pressure on the crankcase and cause it to have issues. Those are best left alone stock and have plenty of HP. Not too mention even in Canada they will nail you with louder pipes.
I can tell you that I had an Ultra as well. While those engines were better then the Mono-Block 580 XLT they can cause issues with the pressure in the crankcase causing them to throw a rod through the block or cause the crankcase to spin a bearing. And I also have friends in Alberta and have said that they are coming down on that kind of stuff. Those were always best left alone with the stock pipe and adding in clutching.