This goes back to the OPs original post. You can have two pressure 'sources'. Pressure from heat and pressure from molecules. With pressure from heat you need to transfer the pressure as quickly as possible because your efficiency losses to the walls of the chamber are greater. In a wankle engine that expansion period is much shorter. I think this is the way you get greater efficiency with water injection in a piston engine, you convert a portion of that combustion temperature to gas.