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Can someone tell me what crankcase cr is ? How you measure it? And also, how in the hell do I measure port open durations???? I'm asking because I think I want to design my own custom exhuast rather than buying one, becuase rcmax is 400+, and Alx is 300+, and those are overseas and I don't know if those would perform the best in my application cuz I use a different cyl and stroke. This is for future reference btw.