Does anyone know of a formula to calculate the minimum big end rod size? I can calculate force, piston speed, etc., and am having custom pistons made, but I want to specify the smallest big end size I can without compromizing the reliability of the rod.

Norm are you meaning the small end of the rod? or are you going to make your own crankshaft as well?

The big end, we can turn the crank to any size we want. I'm trying to get as much stroke as I can within a fairly confined space.