Quote:

One problem is that the "50% factor" has no mathematical or theoretical basis - it's "what works".
It fails to account for the fact that almost all of the rod's small end is not pure reciprocating weight, that material above the pin center is traveling opposite the rod beam, that the difference in forces between long and short rods is completely absent, and that other very large forces (cylinder pressure and vacuum) are completely ignored.
De-constructing over and/or under-balancing to justify an observed result is not science, it's rationalizing.

Read my article here: http://victorylibrary.com/mopar/crank-bal.htm



the very last paragraph sums up my feelings on this subject in regards to Brad's question.
when someone asks the same question and is building a formula 1 engine or something with a 6.0 inch stroke, my reply would most certainly be different.

machine shop owner and engine builder