High speed Deutz Diesel engines are characterized by modular design and air cooling. Turbocharged, charge air cooled engines feature an air-to-air cooler which is an integral part of the engine cooling system.Engine air cooling allows for two basically different charge air cooling system arrangements, whereby the cooler can be placed in-line or parallel to the engine cooling system.In this study, the characteristics of both arrangements are highlighted and their influence on the emission quality of the engine assessed. The comparison between both systems, related to the same engine rating, is based on the U.S. Transient Test Procedures. Furthermore the influence of different engine configurations and the engine temperature control system is described.