Nowadays, modern vehicles comprise a vast number of components made from various materials and manufactured using different techniques, making the management of assemblability, functionality, and cost highly complex. This complexity necessitates controlling geometrical and dimensional deviations to meet product and process demands. Dimensional Management (DM), supported by standards such as ASME-GD&T and ISO-GPS, is increasingly employed for geometrical specification and tolerance analysis. Through Computer-Aided Tolerancing (CAT) tools, tolerances can be considered early in the design process using Design for Tolerancing (DfT) approaches. This study aims to develop and define a methodology for geometric specification allocation and tolerance stack-up analysis of automotive components. The methodology integrates predictive models, DM, and DfT approaches via computer-aided tolerance specification and analysis, enabling comprehensive modeling and simulation of tolerance effects on performance, quality, and assemblability. By applying this methodology to a vehicle engine assembly, its feasibility and effectiveness are demonstrated, showing how the integration of CAT tools and theoretical approaches can significantly enhance design accuracy and efficiency.