Yikes! I just retired from an old
industrial manufacturing plant as a maintenance tech. When I say old I mean 70 year-old bucket elevators, screw conveyors, rotating equipment, etc. I've replaced a lot of motors and gearboxes....
I also have a Dirty Hands 28-ton log splitter. It seldom stalls out on any piece of wood. There is NO combination of motor/ gearbox that I'm familiar with that would come close to performing like my splitter..... unless you go real big and expensive? Anything below a 10 horse motor, with complimentary sized gear box, would probably shell out the gear box in no time? Or over heat the motor constantly and shorten it's life?
I'm not an engineer, just a farm boy/ construction/ maintenance guy. I believe that the engineers of this world would have already figured out how to do this already, if it was financially efficient to do so.
But, hey, if you're just playing around... try a 5 HP motor, 1100 RPM, 40-1 gear box with sprockets or sheaves to go even slower.... and ONLY split short pieces of straight grained wood. Make sure you have motor overload protection, 20 amp circuit, and a big hammer to beat the wood off of the knife (cuz reversing this thing might be a problem?).