[oldman]

The true problem is the 50% reciprocating weight is just a rule of thumb. It just happens to work, there are some over-balancing that also just works. The big end is rotational, the small end and piston is reciprocating. Anything in between is hybrid. My drop in rods are longer than stock, my piston has a different pin height, these small changes affect the hybrid portion of the weight. so 50% to 51% seems to work. Heck these cranks are entirely missing the two center counterweights.. as "good enough". Even things like the center of mass, are you talking geometric or ballance (mass center)? There is a 3% flex right there. Nutshell is it probably is very important that all rods weight the same, and that their weight distribution is the same, factory cast rods are very good vs old fashion forgings. Modern cnc rods even better. Pistons weight the same and 50% of the total is recipricating as a rule of thumb. Is that cener of gravity or is the geometric center is a whole other can of worms. Long stroke short rods engines function differently vs short storke long rod engines but we still use the 50% factor which "just works" but it is NOT based on what is actaully going on inside the engine. I'm more of a inline engine and as long as the stuff is the same weight like pistons... no balancing is required.

Given all this, I just trust, because it lets me sleep better at night. IMO a engine above 850 HP should really go with much thicker I beam rods and stronger thicker pins and to a lesser extent the piston, the whole thing rebalanced. The factory rod is pretty thin IMO and trying to mimic the weight (not the distrubtion) makes for a non-optimal rod. Good enough but at some point you should get "real rods and piston and pins" and rebalance.

Thanks for the good work DorkM. I should have weight mine, I just went off the mfg documentation.