I'm by no means an expert when it come to Marine Applications, But I'll chime in because I'm bored.
My experience with street engines showed me how Forged pistons expanded a tad more at temp than cast ones did, being much denser, forcing a slight overhone to compensate and cold piston slap was pretty normal. Didn't have the "Hyper" dealios back in those days, so not even real sure what they even are. My best guess is a form of heat treating and coating a cast piston to simulate true forged pistons and a lesser cost. I just use forged, and will continue to do so regardless of application.
Given our marine applications, save for closed systems, but for our sake, we NEVER see "Normal" operating temperatures, which would throw the normal equations for street use out the window. So I think, maybe, where Dave is headed is on the expansion characteristics of cast aluminum vs. forged aluminum, and how the "Hypers" inadvertently hinder themselves trying to be one but made from another. I have a metalurgical explanation in my lil brain, but it'd take me an hour to explain it.
Ray
