This paper recounts a brief history of Ford high speed direct injection (HSDI) diesel engines; from the original 2.5 litre naturally aspirated (NA) engine introduced 10 years ago as the world's first high volume HSDI diesel, followed by the introduction of the turbocharged version in 1992 with drive-by-wire electronic fuel injection pump, to the latest low emission version developed to meet recent European Commission (EC) “Stage 2” 94/12/EC standards. The performance development of a prototype 4-valve per cylinder version of the 2.5 litre engine is briefly described, covering the fuel injection equipment, exhaust gas recirculation (EGR) tolerance, regulated emissions capability including the important oxides of nitrogen (NOx) and particulates trade-off, and the performance potential of this combustion system. It is concluded that the 4-valve per cylinder configuration provides significant benefits for emissions achieving a superior NOx/particulates trade-off compared to the 2-valve version of the same engine. The performance potential is demonstrated by the achievement of 16 bar BMEP peak torque. It is finally concluded that this technology will enable light-duty diesels to meet the forecast European emission standards due at the end of this decade and remain the most efficient prime mover for passenger cars and light trucks.