The longer rod in most cases will help because it reduces side load on the piston and permotes better sealing of the rings due to piston rock. Ofcourse the higher up you get in the piston with the rod the less rock anyway. I think there's also a theory that the piston travels faster on the down stroke with a longer rod, but i don't know how that works. If you look at the Nascar guys, they are running real short pistons, 3.2 stroke and 6.2 lg rods with the sm/blk chevies and i don't think they base that on theory, but instead what works best, produces power, and what runs longest without losing power from piston and ring wear.
How much HP gain? i don't know :wink: only the the car will know.
JMO
Zip.