Traditionally the optimization of a turbomachinery engine casing for tip clearance has involved either 2D transient thermo-mechanical simulations or 3D mechanical simulations. The following paper illustrates that 3D transient whole engine thermomechanical simulations can be used within tip clearance optimizations and that the eciency of such optimizations can be improved when a multi-delity surrogate modeling approach is employed. These simulations are employed in conjunction with a rotor sub-optimization utilizing surrogate models of rotordynamics performance, stress,