Yeah, from what I know, 4 cylinder engines are inherently inbalanced, so manufacturers have to weight-balance the crankshaft and pulleys to compensate for the imbalance. I would use a stock pulley to replace your broken one. 3 and 6 cylinder engines are inherently balanced pretty well, so I *might* replace the pulleys on a V6, I6, or I3 (or W12).

 

Ok then. Thanks a bunch for the help!