This study conducts an optimization analysis of the geometry of an intake manifold of an internal combustion engine by using a numerical approach based on the 1D GT-POWER simulation platform. The optimization process was modeled using the Brent method, during which calculations are made of the lengths of the intake manifold runners that provide the engine's greatest volumetric efficiency at each speed of rotation in the range of 1000-6000 RPM. Having obtained the optimized lengths of the runners, it was possible to simulate the engine operating with the parameterized intake manifold based on the length of each runner. From the analysis of the volumetric efficiency curves based on the speed of rotation for the length of each runner of the manifold, it was verified that the shorter the runner length, the greater the volumetric efficiency that occurs when the engine is under high speeds of rotation. Based on the behavior of the volumetric efficiency curves, a variable configuration of the geometry of the intake manifold was proposed. The results of the performance of the engine when operating under this proposal showed that the engine can achieve higher values of volumetric efficiency, torque and effective horsepower, depending on the speed conditions, and consequently lower values for the brake specific fuel consumption.