In this work, an external air and EGR emulation facility has been designed that can replicate a wide range of boosting and EGR delivery systems to a multi-cylinder engine platform. The facility works by removing the incumbent air path and replacing it with externally boosted fresh air that is conditioned using a transient flow and temperature controller. The facility also recycles the actual exhaust gases from the engine whilst removing the constraints of required pressure differences to drive this flow. The resulting system is able to control the boundary conditions of intake air flow - pressure and temperature, engine back-pressure and EGR flow rate independently. Three testing approaches have been described that allow to obtain valuable data across a wide range of the engine map (based on an example of a 1.0L direct injection gasoline engine) also beyond its typical hardware related limits. The facility is designed to be used as part of an engine design optimisation process. The facility generates data of the engine combustion system independently of the associated air path subsystems and excites the boundary conditions beyond those that would be expected from a specific air path design. The data is then used to populate 1D engine models which can be confidently used to predict the performance of a specific air path hardware combination and control strategy.