It is critical for gas and dual fuel engines to have improved transient characteristics in order that they can successfully compete with diesel engines. Testing of transient behavior as well as of different control strategies for the multi-cylinder engine (MCE) should already be done on the single cylinder engine (SCE) test bed during the development process.This paper presents tools and algorithms that simulate transient MCE behavior on a SCE test bed. A methodology that includes both simulation and measurements is developed for a large two-stage turbocharged gas engine. Simple and fast models and algorithms are created that are able to provide the boundary conditions (e.g., boost pressure and exhaust back pressure) of a multi-cylinder engine in transient operation in real-time for use on the SCE test bed. The main models of the methodology are discussed in detail. These models also describe the transient behavior of the complete air and exhaust gas path along with transient turbocharger behavior. The use of classical 1D flow modeling is not applicable due to the long calculation times; instead, the MCE gas exchange is described using a quick 0D approach to guarantee the real-time capability of the models. Additional challenges for a successful application of the methodology involve considering the particularities of numerical calculation, implementing the methodology into a real-time controller and achieving sufficient model robustness to avoid calculation errors. An adequate interface between the MCE model and the SCE test bed is required for the model to interact with the hardware. Finally, the models are implemented and validated on the SCE test bed.