A robust analytical process for evaluating the effects of engine component design on the powertrain NVH has been developed. The work presented focuses on design modifications for refinement of the NVH levels and sound quality of a 4 cylinder Boxer engine with automatic transmission. Assessment focuses on the powertrain structure, cranktrain, torque converter and valvetrain.Comparison of predicted mount vibrations with measurements on a fired engine are made. Through detailed post-processing of the analysis results, looking at modal contributions, modal excitations and loading contributions, the causes and contributions to the NVH are understood and used to direct potential modifications to the powertrain and component design. The models are used to quantify the relative benefit of these modifications in terms of both overall vibration levels and sound quality through implementation of a rumble metric.Furthermore the paper demonstrates the necessity for co-simulation of the powertrain dynamic response with the dynamic motion of the cranktrain and valvetrain components due to the high level of interaction between the systems.