The aim of this thesis is to study the possibility of varying the geometry of the combustion chamber, and consequently the compression ratio, in a four-stroke spark-ignition engine, with the goal of optimizing the engine's performance under all operating conditions. By modifying the internal geometry of the cylinder, it is possible to increase or decrease the pressure exerted by the combustion reaction on the piston head. The geometric characteristics of the cylinder and piston head affect both the chemical and mechanical parameters of the combustion reaction occurring inside the cylinder and, consequently, the power transmitted to the crankshaft. However, varying the pressure to which the mixture is subjected before ignition, triggered by the spark plug, may cause engine damage due to the phenomenon of knocking.