A full 3D Large Eddy Simulation (LES) of a four-stroke, four-cylinder engine, performed with the AVBP-LES code, is presented in this paper.The drive for substantial CO₂ reductions in gasoline engines in the light of the global energy crisis and environmental awareness has increased research into gasoline engines and increased fuel efficiencies. Precise prediction of aerodynamics, mixing, combustion and pollutant formation are required so that CFD may actively contribute to the improvement/optimization of combustion chamber, intake/exhaust ducts and manifold shapes and volumes which all contribute to the global performance and efficiency of an engine.One way to improve engine efficiency is to reduce the cycle-to-cycle variability, through an improved understanding of their sources and effects. The conventional RANS approach does not allow addressing non-cyclic phenomena as it aims to compute the average cycle. LES on the other hand is particularly well suited to study unsteady flow effects and grants access to the description of cyclic variations. When considering multi-cylinder engines, cylinder-to-cylinder interactions are crucial issues. Consequently, the whole engine has to be represented for a fully realistic simulation.The present study aims at illustrating the innovative usage of LES to reproduce and understand unsteady flow interactions between the cylinders of a four-cylinder gasoline engine. To achieve this purpose, more than nine cycles of the full engine were computed. The computational domain covers the whole geometry, including four combustion chambers as well as the intake and exhaust ducts and manifolds. Details on the methodology used - based on the AVBP LES code - and on the results obtained are given. Cylinder-to-cylinder and cycle-to-cycle discrepancies are shown and Fourier analysis is used to understand the cylinder-to-cylinder influence.