A high performance overhead valvetrain assembly includes a hydraulic lash adjuster which is received within and supports a trunnion. The trunnion, in turn, is received within a cylindrical passageway in one end of a rocker arm. The opposite end of the rocker arm engages a valve stem. Between the trunnion and the valve stem is a roller adapted the engage a cam of a camshaft. The trunnion stabilized rocker arm permits significantly increased valve lift and improved engine performance.