Methods of reducing the noise level of a diesel engine include the suppression of the major modes of block vibration and treatment of the external surfaces. Design methods enable the frequencies and noise levels of these modes to be calculated for a conventionally designed engine.The important modes of vibration, the noise signature and the effect of block modifications of a standard production V-8 engine were found by experiments. These provided the basis for the design of an experimental low-noise engine. Design features include a suffer block, removal of the bottom part of the crankcase skirt, the addition of a single bearing beam, and the use of isolated panels and damped surfaces. The noise reduction obtained was 9 dBA. Most of this is due to the use of isolated and damped nonload carrying surfaces.