> To do this, Porsche's patent shows a crankshaft spinning on a ring with two concentric circles—an annulus. ... this engine has two top and bottom dead centers

> To do this, Porsche's patent shows a crankshaft spinning on a ring with two concentric circles—an annulus. ... this engine has two top and bottom dead centers. Instead of doing this complicated crankshaft, I wonder if you could do this with opposed pistons. The difference between the two top dead centers (and bottom dead centers) is small, so the secondary piston wouldn't have to move far to create the same change in volume. I can see some advantages and disadvantages. The crankshaft gets simpler, but you need to move the secondary piston somehow, presumably off the camshaft? Which sounds pretty rough on the timing chain. Also, it would have to go where the valves currently are. And another piston ring to wear out. On the other hand, the crankshaft gets simpler, and it's a critical component since it's transmitting all the engine power. Also, with the opposing piston, you could use a cam to get greater control of exactly when the volume changes happen.