This paper is related to the load transient modelling of heavy-duty (HD) turbocharged diesel engines with a wave action model. The control variables of this transient are analysed and the modelling alternatives reviewed. Afterwards, the developed computer model is described as well as the novel sub-models. The model predictions are compared with the experimental results for validation in a six-cylinder HD turbocharged engine at different engine speeds. The evolution of engine variables, difficult to measure experimentally during the transient, as the instantaneous relative fuel to air ratio, FR, are computed with the model and analysed. These parameters provide very meaningful information of the transient evolution. As an example of the model application, the influence of the intake manifold tuning on the transient evolution is evaluated.