This paper is about downsizing for off road vehicle diesel engines. While fuel efficiency has to be improved, future Diesel engine emission standards will further restrict vehicle emissions, particularly of nitrogen oxides. Increased in-cylinder filling is recognized as a key factor in addressing this issue, which calls for advanced design of air and exhaust gas recirculation circuits and high cooling capabilities. Two stage turbocharging applied to off road diesel engines is a promising solution for enhancing rated power, low end torque, transient performance, better low-speed torque, longer turbo life and optimized fuel efficiency. In the new engine design, two turbochargers are arranged in series to generate increased air pressure, airflow and a superior turbocharging effect. At high altitudes, 2-stage turbocharging technology guarantees the engine's operational performance by compensating for the reduced air density. However, a trade-off is required to match some conflicting issues, i.e. overall dimensions, cost, emissions control and performance. The outcome strongly depends on the specific constraints and goals of the project. In the paper, reference is made to 3.21L, 4 cylinder in-line diesel engine for off road application. The development methodology used to achieve high pressure ratio turbocharging is discussed; along with operating limitations. The study demonstrate that, on the off road vehicle engine, the use of a super charging system made up by a low pressure turbocharger and high pressure turbocharger is able to noticeably enhance engine performance at full load, with further advantages, in comparison to the other analyzed system, in terms of fuel consumption and emission control.