For developing high-quality and cost-efficient products, it is important to evaluate and compare system level performance for different configurations early in the development process. This paper will present the development of a vehicle system model in Modelica that is used to study the overall vehicle power-train torsional vibrations that impact Noise, Vibration & Harshness (NVH) characteristics of the vehicle. In this study, a detailed crank-angle resolved, multi-cylinder engine model is constructed, which includes intake/exhaust dynamics, combustion, heat transfer, engine friction and rotational dynamics of piston-crank mechanism. The engine model accurately reproduced real-world engine torque and acceleration fluctuations. The lumped parameter powertrain system model which includes clutch (and associated vibration isolation components), transmission, driveline and chassis is developed and used with the engine model to predict torsional vibrations. This system model is used to understand the powertrain torsional vibration characteristics in different operating regions such as idling, driving and coasting conditions.To demonstrate the applicability of the developed models, results of unit tests for independent components, especially the engine torque variation and the clutch torsion characteristic, and the system-level quantitative validation with test data are presented. A special model that does fast Fourier transform of the signal on the fly is presented and its role in the analysis discussed. We present a comparison of rattle noise between two compliant clutch (isolator) designs and discuss the rattle metrics used in the analysis. Generic considerations for the deployment of such system level models are also discussed in this paper.