Engineers need the most capable design support tools to reconcile the demands of the market, legislation, economic design and production. Simulation tools are a very effective support system.The optimization of the complete vehicle system for external noise radiation is very complex due to the interaction of the engine performance with the vehicle positioning. Simple predictive methods and assumptions are often not usefully accurate. The work described here covers an approach to combining rapid predictions of engine and vehicle performance with those of radiated noise from the various significant subsystems, to produce a useful, rapid, prediction tool for complete vehicle noise. A mono-dimensional gas flow code is used to provide a sufficiently accurate prediction of the engine power for vehicle performance prediction and also the noise output of intake and exhaust systems.Various approximate prediction methods are used to assemble an overall vehicle radiated noise prediction. This takes account of vehicle performance, size, component location and sub-sources such as the exhaust shell noise. The derivations of the approximations and the assumptions in the code are given. The results of various examples illustrate the overall effectiveness of this combined approach to vehicle noise modeling. Continuing development is underway which uses an improved flow code (GTPower) which effectively covers both the engine pipe gas flows and the performance modeling, including the acoustic radiation from the intake and exhaust.