The paper describes the results achieved in developing a new diesel combustion system for passenger car application that, while capable of high power density, delivers excellent fuel economy through a combination of mechanical and thermodynamic efficiencies improvement. The project stemmed from the observation that by increasing the fuel injection pressure it is possible to increase the engine power density while maintaining the engine peak firing pressure constant. Conversely, it was conceived the idea that, by leveraging the high fuel injection pressure of last generation common rail systems, it is possible to reduce the engine peak firing pressure with great benefits on reciprocating and rotating components light-weighting and friction, while keeping the power density at competitive levels. Following extensive benchmark and analysis activities in order to identify the key design parameters to be optimized, an advanced injection system concept capable of injection pressure greater than 2500 bar was coupled to a prototype engine featuring newly developed combustion system. The matching among the low compression ratio wide bowl, the in-cylinder charge motion, the highly efficient injector nozzle and the injection pressure have been thoroughly examined and experimentally parametrized. The tests confirmed the benefits of the employment of high fuel injection pressures as a way to reduce the peak firing pressure, combining competitive performance and excellent fuel efficiency with emissions and NVH requirements of last generation diesel engines for passenger car applications. The paper discusses the engine power and efficiency sensitivities to the boundary conditions of the charging/exhaust systems, the available maximum fuel injection pressure and the mechanical base engine design (with particular reference to the peak firing pressure). Consequently, a balanced set of targets for the entire system based on such results are carried out.