hello Ed. thanks for the comment and i hope you will keep an eye on me with this project to keep me from screwing up to much. i built your tin can stirling and had a lot of fun with it and i follow all of your post and your web site. the heat exchanger built into the stack should get super hot and with one third of the hot end of the displacement chamber installed inside the exchanger, i should get a very quick buildup of heat pressure in the chamber, to drive the rod. i am still studying the principle of the stirling and have researched everything i can find. i think the two-piston engine design from Anerican stirling will give me the best proformance for this setup and i would like to have multiple engines turning the same crankshaft. the design is something like a v6 auto block arrangement with three hot chambers (imbedded in the exchanger) on one side and three cooling chambers (encased in a water jacket, on the other side and a short pipe for air exchange connecting the hot and cold chambers. i have not desided on a size yet, but leaning toward six inch dia. because i have some thick wall six inch metal pipe that should hold the heat and give me about six inches of rod travel on the heat side. hope it works, pepa