The application of variable-geometry turbocharging (VGT) and high-pressure common rail (HPCR) fuel injection systems to the automotive diesel engine offers substantial flexibility in both air charge and fuel management. This flexibility allows the VGT to deliver optimised boost levels over the engine's wide operating speed compared with a fixed-geometry turbocharger (FGT). The HPCR system, having the capability to deliver fuel injection pressures independent of crankshaft speed, as well as the capability for multi-injections per cycle, extends the ability to optimise the fuel/air mixing mechanism. The studies reported in this paper have been specifically undertaken under limiting torque conditions on a 1.8-1 prototype direct injection diesel engine with a baseline build consisting of a FGT with a distributor electronic fuel injection system. The baseline build has been upgraded to include, in the first instance, a VGT followed by a further build incorporating a HPCR system. The VGT studies show a 15% gain in torque at 2250 rev min(-1) over an equivalent fixed-geometry turbocharger build of engine. This torque increase is achieved without severely compromising fuel consumption and smoke emissions. The HPCR system demonstrates the potential for smoke and combustion noise reduction and the 'on engine' operating characteristics of these first generation systems are explained in some detail.