Steve, the Honda is a horizontal shaft and the 31 Briggs is vertical, unless you turn it on its side, like I did. A horizontal shaft engine with a jackshaft will make a little more power than an identical vertical shaft motor with a tranny or a 90 degree box, because of the extra drag created by a tranny or a 90 box. With that being said, the Briggs I used to run made more power on the bottom end than the GX390. The 390 has a little more on the top end. On most of the tracks we run on, having more bottom end to get you up out of the turns, will help you out more than having a little more top end. I think I would prefer the Briggs, IF I could keep the cranks from breaking! The Honda seems to be more reliable. I am running a precision cam, 1.2 to 1 ratio roller rockers, ARC rod, forged piston and stainless (stock size) valves, with EC double valve springs and chromoly push rods in my GX390, and a lot of time spent on the head. I also run a Walbro LMT carb and a home made intake on it.
