The port volume has been reduced and as a result the velocity has increased. Because of the windows in the piston, I suspect the overall efficiency has been improved. I noticed on the sticker it is CARB approved. The exhaust produces almost no smoke and in the old 25 the same fuel smokes profusely.
Before I test this engine, I will match and contour the crankcase flange to the cylinder, knife edge the port divider and contour the windows in the piston. This should greatly increase flow through the bypass ports. It is amazing how much flow is increased by just knocking off the rough spots. A noticable power increase can be seen by putting a high polish on the piston top.