These cranks are precision balanced if ordered as a BC stroker kit, bobweights required if using own piston and/or rod combo. 4340 billet crankshaft in +4.8mm stroke (71mm). MUST USE WITH SIDEWINDER OIL PUMP/SPROCKET. All cranks are stress relieved, shot peened, magna flux inspected and nitrided (multi step heat treatment) for ultimate performance. Fully profiled counterweights are designed for reduced windage through the crankcase creating less oil resistance for better rpm potential. These cranks must be fully system balanced prior to installation due various bobweights. Add $125 for precision balancing to bobweights you provide.