Malone Engine

http://en.wikipedia.org/wiki/Malone_engine

We haven't looked into this one. If indeed 27% efficiency has been reached with 1930 technology - this is worth examining further. The highest documented efficiency that I read about for steam was 22%, from 1980 (Dutcher Industries). Contact the people in the 3rd Wikipedia reference to get the lowdown - or put me in touch with them and we can assess the situation further.