I am also considering a 4.125 crank for my fully ported SB edddie heads. What I'd like to know is would it be cost effective to replace my 4" crank 10:1 motor with a 4.125 crank and 11.5 motor? The heads aren't ideal, but would they still build more HP on a bigger CI motor? The extra compression and cubes will allow for a bigger cam. My hydraulic roller is all done at 6000RPM anyway. In my mind, a 40-50HP bump would justify the expense. I just don't know if we're at the law of diminishing returns with the eddies and these big cranks.
Tom