The goal of this Master thesis is to analyse how the hardware selection and validation phases of the development process of a small displacement off-road brand-new engine are structured. First chapter presents the project from the beginning, introducing market-based design choices, briefly explaining the compression ignition combustion process with subsequent pollutants formation in a diesel engine and emissions regulations in Europe and USA, respectively Stage V and Tier 4 Final. Chapter 2 describes the naturally aspirated engine version features, explaining peculiar characteristics of an IDI diesel engine, with its subsequent architectural distinguishing elements: prechambers and pistons, injection system and a short consideration on TC and TCA versions.