A test rig is provided for dynamic or static testing of a vehicle powertrain apparatus during operation in varying attitudes. A specific embodiment includes inner and outer frames carried one inside the other on gimbal bearings and pivotable on longitudinal and transverse axes. The inner frame carries a cradle for mounting a dynometer connected to an engine, transmission or other apparatus to be tested by tilting the apparatus to simulate the effects of vehicle acceleration in various directions. The rig may be supported on individual stanchions mounted to a test bed floor plate in an engine test cell and supporting the bearings for the outer frame. The pivotable frames are powered by electric motors through reduction gear boxes sized and mounted to minimize mass and inertia of the rig and allow mounting in an engine test cell. Programmable controls permit dynamic rocking of an engine operating under power.