Abstract: A limited leak-down variable duration lifter and its adjustment is provided to maximize performance gains at low engine rpm when used with a conventional cam and more particularly with a conventional hi-performance camshaft. The increased performance gains were here-to-for unobtainable with conventional variable duration lifters and the conventional adjustment. By utilizing an adjustable valve train to precisely position the plunger of an accelerated leak variable duration lifter near the bottom of its travel, optimum reductions of lift and duration are achieved without exceeding amounts that would be detrimental to the engine and its valve train. To maintain proper rocker arm geometry, the plunger is positioned closer to its seat in the assembled state by either reengineering the internal dimensions of the lifter, or by providing a spacer or spacers between the plunger and the push rod cup, or plunger and seat.