Stay with Matt on this. WHen you look at the crank casting numbers------same. But reciprocating mass is lighter. Balancing (mass rotation) "sees" 50% of the upper weight (rod small end, piston, rings, wrist pin) and 100% of rod throw mass (rod big end, rod brgs, and crankshaft throw) It wouldn't appear to be a big deal but it is. Sad part is, I have found more main brgs wiped out and junked worse than the rod brgs and crankshaft rod throws. Go figure. Balance it to your app. Harmonics under this condition will cause a bunch of grief.