The paper describes the challenges and results achieved in developing a new high speed Diesel combustion system capable of exceeding the threshold of 100 kW/l. The high-quality state-of-art components of the automotive diesel technology was provided in order to set-up a single-cylinder research engine demonstrator. Key design parameters were identified in terms boost, speed, injection pressure and nozzle flow rates. In this regard, an advanced piezo injection system capable of 3000 bar maximum injection pressure was selected, coupled to a robust base engine featuring advanced combustion bowl and intake ports. The matching among the low compression ratio wide bowl, the high-density charge motion, engine speed and the highly efficient injector nozzles have been thoroughly examined and experimentally parametrized. The tests confirmed the benefits of the employment of very high fuel injection pressures as a way to solve the above-mentioned trade-off, combining high performance and fuel economy for light-duty high-speed diesel engines. The paper discusses the system sensitivity to the boundary conditions of the charging and exhaust systems, and develops a balanced set of targets for the entire system based on thermo-structural, fluid-dynamics and efficiency considerations. This would represent, in the authors' view, the 'recipe' for the next generation of high-power density diesel engines for road transport application.