Crankshafts are subjected to complex forces and torques which vary continuously with location and time. A nonlinear crankshaft dynamics model is developed on the basis of a dynamic simulation language. The model comprises compression and combustion forces, dynamics of oscillating parts, spatially distributed inertial and elastic effects on the crankshaft, and dissipative effects. The model is validated through experimental records of crankshaft torsional dynamics on an eight cylinder Diesel engine, comprising wide ranges of engine torsional loads and speeds. The analysis of crankshaft dynamics allows to determine the computational requirements for the determination of the instantaneous engine torque. Such instantaneous torque measurement is of interest for improved performance and emission control.