It is well understood that stress stiffening affects the dynamic response of a structure. Just as tightening a string changes the tone produced by a violin, tightening head bolts changes the dynamic response of an engine block assembly. While fundamental to nonlinear static stress analysis, stress stiffening effects are most often ignored when evaluating the steady-state dynamic response of engine assemblies. This article highlights the impact of various bolt loading assumptions on the flexibility and steady-state dynamic response of an engine head and block assembly. Including assembly load effects in the simulation workflow allows for more accurate prediction of system-level performance, such as engine radiated noise.