The IDI diesel engine still offers a substantial development potential. One major advantage is its low fuel consumption and, hence, its low CO2 emission compared to gasoline engines. The disadvantage of its higher noise emission, however, requires particular attention in the development stage. By means of modern signal analysing and signal processing methods in combination with computer simulation methods new tools for the development of low noise Diesel engines are available.The noise emission of IDI diesel engines has on average been reduced by about 5 to 8 dBA within the last 15 years. This trend will continue further despite the introduction of more and more light weight design components.Today's IDI diesel engine is mainly dominated by high noise levels in the frequency range about 1600 to 2000 Hz. In-depth measurements show that this is generally caused by a high combustion excitation (Helmholtz-resonance) and, in addition, structure weaknesses of the crankcase. For the development of low noise IDI diesel engines particular attention has to be paid to the combustion excitation and/or structure behaviour in this particular frequency range.An acoustical assessment of the engine block structure already in the design stage can be achieved by using dynamic Finite Element techniques. On the basis of the particular combustion excitation of IDI diesel engines the surface vibration will be calculated by forced response analysis. Structure detail modifications lead to a low noise engine design. This design process and the consequent optimization has been successfully applied to an IDI diesel engine.