Forged steel crank and I have to check the chamber that those pistons need i don't have the spec. sheet with me now. Clarkes Machine shop gave me the cc chamber I needed to get the high compression but I don't remember off the top of my head. I'm building a boat that this was going to go in but I ran into a couple snags so I won't be using it this year and I need a float to get me through the summer.