A torsionally de-coupled engine mount system (13) for use in tilt rotor aircraft (11) applications is disclosed, in which an engine is mounted at its forward end to a prop rotor gear box by means of a forward mount (303) that is a simple adapter fitting, and at its aft end to a pylon assembly by an aft mount (305) that is a simple bi-pod fitting. The forward mount (303) counteracts forces and moments in six degrees of freedom, but the aft mount (305) only counteracts lateral and vertical loads. The contribution from the engine to the overall dynamic response of the aircraft is tuned by selectively tailoring the size, shape, weight, and material of the forward mount (303). The engine mount system torsionally de-couples the engines from the prop rotors, thereby preventing rotor torque from being induced into the engines. In addition, the contribution from the engines to the overall dynamic response of the aircraft can be tuned by selectively tailoring the size, shape, weight, and material of the forward mounts between the engines and the transmissions.