The new style little giant is much better then the old style, the guides and control are much better. The Alabama forge council has drawing for the latest air hammer circuit and suggested parts list...on there web page. A 4 " cylinder would take 35 to 50 cfm's, I think I would stay with the 2 1/2 "diameter one.. I run one on a 17 cfm 2 stage...works great... Mike Wolfe www.designsiniron.com