Stiffener ribs are widely used to increase the stiffness of engine blocks, shifting the vibration modes to higher frequencies where excitation is weaker so that radiated noise can be reduced. The effect of different rib design parameters on the radiated noise emission of a diesel engine has been investigated considering its impact on block weight. A heavy-duty engine block was modeled using finite element method, multi-body dynamics approach was used to determine the excitation forces acting due to combustion pressure and inertias, and boundary element method was used to find the acoustic transfer vectors which give the relationship between engine surface velocities and sound pressure levels at predetermined microphone locations. Initially, the baseline analytical sound pressure level and surface velocity results for the engine without ribs were obtained. Two prototype engines, with and without stiffened ribs, were tested in an acoustic dynamometer in complete speed range. Then, the problem was narrowed down to a specific surface patch on the block at a critical engine speed. The effects of various ribbing design parameters have been identified iteratively. A noticeable decrease in engine noise can be achieved by increasing the number of ribs, using thicker or higher ribs particularly in the frequency range corresponding to the engine skirt breathing modes. Increasing the rib height was found to be the most efficient way to reduce noise emissions with least impact on the block weight.