The addition of a constriction in the melt flow path of high pressure die castings is discussed in terms of its influence on modifications to mechanical properties. It is shown through experimentation that the ultimate tensile strength and elongation to fracture of as-cast tensile specimens increased when the melt flowed through a constricted path. It is proposed that defect-forming inclusions were disintegrated more efficiently in the constricted runner through increased strain rates and turbulent dissipation rates. Increased turbulence is also presumed to be the cause for the greater dispersion of defects. The suggestions are supported with calculations aided by computational fluid dynamics simulations.