I was appending this note to my last post but it seemed to be a new thread. I was doing a valve job on my old Toyota pickup and marveled at the weight of the timing chain and valve springs. I thought - it takes a lot of energy to throw those valves up and down at speed. It seems that an alternative to the reciprocating valve would be a great advance, and some kind of rotary device makes (theoretical) sense. There's great website Museum of Retro Technology, which has an almost encyclopedic listing of engine designs (EC and IC). The owner, Doug Self, is very pessimistic about rotary anything, and documents the sad history of failed attempts to make rotary valves. I'm not saying I can buck the trend, but I'm going to try (fools rush in). There seem to be several possible topologies which offer great efficiencies in terms san er energy and reduction of moving parts. Each with its own problems. Clearly seals are one of the big issues. I'm intrigued by the possibility of labyrinth seals. The shapes I've thought about include: 1. rotating variant of spool valve, 2. hollow rotating tube valve, 3. rotating disc 4. etc If anyone would like to discuss these issues, I'd be glad to hear from you. thanks!