In the automotive industry simulation represents an essential tool for the development process of the functions designed and integrated within the Engine Control Unit (ECU). This approach applies to each stage of the development cycle to establish the possible physics which are modeled accordingly. The particular stage which relates to the validation of the Engine Control Unit uses test benches called Hardware In the Loop (HIL) systems. They simulate both engine and vehicle by means of integrated models. The characteristics of these benches represent the constraints for the real-time computation of these models, in particular when the Engine Control Unit test requires a highly detailed physical model.This paper attempts to treat the introduction of plant models based on a more accurate physical representation of the internal combustion engines into a Hardware In the Loop target. Using AMESim® simulation software, the model reduction constraints are exposed, in order to get the appropriate results on the HIL target. Finally, results obtained with a naturally aspirated gasoline application are presented. Turbocharged applications are under development.