A non-linear mathematical model has been developed to predict the transient response of a turbocharged diesel engine. The quasi-steady “filling and emptying” concept has been employed in the analysis of the thermo and fluid dynamics under transient engine conditions. In addition, by continuously evaluating the dynamic interactions of engine components, major limitations of previous linear and quasi-linear models have been overcome.A computer controlled test-bed and high speed data logging system has been used to acquire detailed data under transient conditions (e.g injection and cylinder pressure diagrams). This data has been used to validate the model, the result being good agreement between predicted and measured engine performance.Application of the model has proved its value in the study and optimization of design variables which affect engine performance and response time. As examples, the effects of using a fuel pump rack limiter and that of rematching the turbocharger in conjunction with an exhaust waste gate are presented.