In this work the vibrational behaviour of a 4-cylinder, 4-stroke, petrol engine has been simulated by leveraging on the Finite Element Method (FEM). A reduced modelling strategy, based on the Component Mode Synthesis (CMS), has been adopted to reduce the size of the FEM model. A full FEM model of the whole engine, comprising all its sub-components, has been preliminary characterized from the vibrational standpoint. Subsequently, the CMS has been adopted in order to reduce the computational burden. Frequency Response Function (FRF) analyses have been used to identify the resonant frequencies and mode shapes of the different FEM models, and the so-obtained results have been compared showing a very good agreement. The reduced model has been able to reproduce with a high accuracy the vibration response at the engine mounts. The adopted reduced modelling strategy turned out to be effective in lowering the computational burden, keeping at the same time an accurate replication of the engine vibrational behaviour. Runtimes have been significantly reduced from 3 weeks for the full FEM model to nearly 2 days for the reduced model.