Three different acoustic finite element models of an automobile passenger compartment are developed and experimentally assessed. The three different models are a traditional model, an improved model, and an optimized model. The traditional model represents the passenger and trunk compartment cavities and the coupling between them through the rear seat cavity. The improved model includes traditional acoustic models of the passenger and trunk compartments, as well as equivalent-acoustic finite element models of the front and rear seats, parcel shelf, door volumes, instrument panel, and trunk wheel well volume. An optimized version of the improved acoustic model is developed by modifying the equivalent-acoustic properties. Modal analysis tests of a vehicle were conducted using loudspeaker excitation to identify the compartment cavity modes and sound pressure response to 500 Hz to assess the accuracy of the acoustic models. The optimized acoustic model is also coupled with a structural finite-element model of the trimmed body to evaluate the effect of body panel flexibility on the interior sound pressure response. The optimized acoustic model is found to exhibit the best correlation in terms of the predicted sound pressure FRF response at the passenger compartment interior locations and at the compartment boundary surfaces.