Balancing of the crankshaft to minimize bearing loads is a critical concern in the design of multicylinder engines, especially high-speed racing engines. In this paper a numerical model is developed for the crankshaft-connecting rod-piston assembly that considers reciprocating forces as well as gas pressure forces. The model is used in an optimization scheme to design crankshaft counterweights which minimize main bearing forces. A V-8 NASCAR engine is analyzed. The results indicate reductions in average bearing force of as much as 73% while peak force is reduced as much as 41%.