Sorry guys I don't have any more specs on Stihl's new blowers yet, although I've heard rumor about an even larger backpack blower on the way...BR600!! Our service rep is about 165 lbs and he says he has to lean into it when it revs...not even in their 2005 literature yet but might be interesting when it arrives. I'll tear a br550 down and weigh the engine and post my results in a couple of days.