Suggest reading.
Crankshaft Balance Factors
It discusses in detail the
various forces that act on the rotating mass of a 4 cycle engine. If you go from a 4 to a 3 cylinder, be sure to carry several containers, some kitty litter, a push broom and a shovel in your 3 cylinder car. The kitty liter
to soak up the engine oil when the rod(s) go through the oil pan. The broom to sweep up the engine parts and kitty litter and the shovel to put the mess in the containers.