Life got in the way. Moved, got new job, divorced, married, baby, promoted, busy busy busy.
By the time I ever get back to that, there probably won't be an internal combustion engine anymore so it won't matter. :\ Although I've still been thinking about it in the back of my mind, and I have a few more ideas how to make it even more efficient. Really the only way I'd ever get this thing built is if I found someone or a group of someones with the means of actually building it and were fascinated enough in my ideas to give it a try on my behalf.