More coals on the fire. The ZDZ-40 is a 3-port motor, the ZDZ-80 is a 6-port motor. Which one do you think would show the best HP/weight potential? A rotary valve or a reed valve engine both have good potential for top end horsepower, but we really don't need power at very high rpm for airplane motors. One of the problems that some reed valve motors have is puddling of the mixture in the crankcase. I have heard people claim that the midrange gurgling of some of the 3W twins (like the 3W-100) is caused by fuel collecting and puddling in the reed cage. I don't know if that's true or not. I do know that 3W did some redesign of their new 150-SS to smooth out the midrange. Apparently, they changed the forward cylinder (left for right) to get less puddling. Reed valves dominate motocross engines (except for the Yamaha 4-bangers) because they need a fat torque curve to accelerate in the dirt. That's also the reason they use exhaust powervalves, to lower the exhaust duration at low rpm and fatten the low rpm torque curve. Since we don't fly our planes in the dirt, we really don't need a fat torque curve at 3,000 rpm, so a powervalve would only add extra weight. For GP roadracing, both Yamaha and Suzuki flirted with rotary valves over the years. Some years they used rotaries, some years they used reeds. Both have potential, but the devil is in the details. In the last couple of years, they started to detune the motors to be easier on the tires. That's why Honda went to the 3-cylinder bikes. Max HP wasn't their goal, but a fast lap time for the whole race was.

The first engine I hopped up was a Kawasaki Bighorn 350. Kaw had a kit that included a big carb, longer duration rotary valve, and a tuned pipe. Hmmm. same as it ever was.