RE: Lower Crankcase shape.
Transition =change, my friends Kawalski 1400 Concours will transition from 15 mph in 6th gear to well above 150 with no hiccups, no bog. My Fox .74 conversion will transition from barely turning to 9,500 with a 12x8 three blade, the medium with which you hook up that transition whether air or asphalt doesn't enter into it.