I certainly don't claim nor believe I understand props - I just go to a reliable prop manufacture and tell told him what I had and what I wanted. When I originally got my 76x88 prop, I decided I wanted 200 more engine rpm and that is all I told Clark Lydic and he cut off an 2" off the diameter and I got my 200 rpm increase. Could have been just lucky, but a good prop guy can give you the right prop - IF you give him the right information.