[BillK]

Joe,
Like the others said, there can be some variations mainly from experience. I think most of the time you see an "overbalanced" engine in a situation where it is run for long time periods at high rpms, like a Nascar engine. Basically you make the bobweight a little heavier than the "normal" formula.

Harley actually has three different recommendations depending on whether the engine is going to be "street", "street high performance" or "strictly race"

A lot of it is more art than science but I don't think you can go wrong with the standard formula on most engines. I have overbalanced a couple for circle track engines but really don't know if there was really any difference.