:This paper presents a numerical model consisting of a two-dimensional, inviscid, stream-function vorticity code with a slotted-wall boundary condition. The model can be used to predict vehicle pressure-simulation accuracy in a slotted-wall automotive wind tunnel for a range of test section configurations. The vehicle and its wake were modeled as a combination of a doublet and a wake source, and the slotted-wall boundary condition was calibrated using published experimental data. Despite its inherent approximations, this model produces results that agree remarkably well with magnitudes and trends observed in published experimental data. This model was used to determine the length needed for a slotted-wall test section containing both a turntable and a dynamometer for aerodynamic as well as thermodynamic testing capability. Tests were conducted on a 1/12-scale slotted-wall test section to confirm the test section length predicted by the numerical model. These tests showed excellent agreement with the results of the numerical model. Validation of this numerical model, as well as results of the numerical and the experimental test-section-length study, are included in this paper.