In direct injection Diesel engines having a unit displacement less than 1 liter, the use of high compression ratios (19\20 instead of 16\17) is mandatory for solving cold smoke problems and reducing HC\NOx emissions. The increase of compression ratio however is associated to the increase of black smoke and specific fuel consumption. On the basis of systematic measurements of the main combustion quantities and 2-D computations of the air motion and spray development inside the cylinder, a re-entrant high compression ratio chamber was defined. Experimental results in terms of fuel consumption, black smoke and gaseous emissions are presented. The optimum squish-to-swirl ratio is discussed.