This paper explains the reasons for applying variable valve timing to a diesel engine, in order to reduce the likelihood of inlet port fouling at part load. The results from a cycle simulation are compared with experimental results, from an engine tested with three different valve timings. Good agreement between the model and the engine is demonstrated by comparisons of experimental and simulation results for both global parameters, and cycle resolved pressure measurements (cylinder and manifolds). The cycle simulation has thus been used to predict the benefits that accrue from the application of variable valve timing to a turbocharged diesel engine. Reducing the valve overlap was found to be beneficial at part load. The greatest reduction in the reverse flow of exhaust residuals into the inlet manifold, was obtained if the inlet valve opening was delayed by phasing the inlet valve events.