I have been working on a small problem for a little while, and I so happen to find this forum. I was wondering if anyone can point me to the right direction with this. I am trying to calculate very accurately how much the rod/piston assembly in an engine will weigh at a given RPM. I have been studying ARP's (Automotive Racing Products) equations from their website, but the numbers do not sound correct at all ( 228,742 kilo's @ 1000RPM? ). So I am kind of skeptical about their math or the way I am doing it. this is the equation and graph http://www.arp-bolts.com/Tech/T0_FastenerEng/T0_Images/FOSTERP1A-c.jpg [Broken] http://www.arp-bolts.com/Tech/T0_FastenerEng/T0_Images/P1-CHARTS.jpg [Broken] My thoughts about this is that the piston and rod are not changing direction instantly, but the rod slowly changes direction in about a 180 degree rotation of the crankshaft, but the change peaks at the bottom and top of the strokes. So I believe there has to be a much more detailed math to describe this. I have an excel sheet i made that has all the work already there. So if anyone could take a look at it and steer me in the right direction with this, that would be cool.