A rotary disk valve or tube valve will certainly work and best of all with our fuel there's no problem with exhaust valve's cooling and lubrication, but if you want ultimate power you need a cam, only in a cam profile you can obtain really high area under the curve - aka WORK, since it gives a non-linear relation between valve position and crankshaft. With a rotary type valva you can only go to a certain point dictated by the linearity of a 360deg circle - the crankshaft. That's the reason you dont see the F1 guys messing with rotary valves, and maybe thus even 2-stroke engines it would actually rob them a ton of power.

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