This paper considers important aspects of rigid body dynamics of power trains with respect to noise and vibration (by definition a power train (PT) term here is an engine plus transmission). Flexibility of PT's and their ancillaries leads to unwanted levels of noise and vibration. By employing rigid body concepts we can assess the levels of unwanted flexibility of whole PT's and their ancillaries e.g. mounting brackets. Using dedicated software based on rigid body theory it is possible to define vibration and noise ‘entitlement’ i.e. minimum vibration and noise that can theoretically be achieved. Targets can then be to set based upon these entitlements. This can then lead to better more robust designs to achieve higher levels of refinement. The use of generic 3 and 4 cylinder one liter in-line PT's modes are used within the software to aid this study. These PT's can be shown to adhere more to rigid body behavior due to their compact designs and lower (frequency) dominant orders of excitation. This paper steps through from basic understanding of rigid PT behavior then shows some rigid vibration and noise results for generic 3 and 4 cylinder PT's at key mount positions it then leads into leads onto how and why rigid vibration theory can help improve refinement with accompanying graphs and schematics to clarify understanding.