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.

Abstract: A self-adjusting variable duration hydraulic lifter utilizes two plungers within the cylindrical lifter body which move together to shorten the overall top-to-bottom length of the internal plunger pair during the valve opening cycle of the engine at low RPM's to improve engine performance. A pre-established gap between the two plungers establishes the bleed down amount for the lifter at low RPM, and the gap is self-adjusting in that it will remain the same over the lifetime of the engine despite changes in the overall length of the valve train and heat compensation effected by the hydraulic mechanism effected by the lifter.

Abstract: Improvements are provided to the variable duration lifter, and the valve train of which the lifter is a part, which have the effect of reducing the tapping noise of the valves at low RPM, which is characteristic of effective variable duration lifters. This is achieved by utilizing an effective length of the valve train which produces a reduced volume of the oil reservoir defined between the outer cylinder of the lifter and the internal plunger, such that when the engine operates at low RPM, the internal plunger "bottoms out" before the valve seats. This is coupled with a modified cam having a closing ramp which seats the valve more smoothly and quietly than does the conventional ramp.

Abstract: A hydraulic valve lifter for use in high performance engines to reduce valve overlap at low operating speeds utilizes a restricted oil bleed passageway leading from the lifter pressure chamber to externally of the lifter to permit oil to bleed from the pressure chamber, preventing the lifter from pumping up to a fully solid condition at low operating speeds; the passageway, however, is sufficiently narrowed to pass an insignificant volume of oil therethrough at higher speeds. This passageway, previously defined as an external flat ground partway up the lifter plunger, is, according to the instant disclosure, ground fully up to the top of the plunger. This permits the plungers to be ground much more easily than before, inasmuch as they can be axially aligned on a magnetic chuck, or the equivalent, with the flat or groove which defines the bleed passageway cut in a single stroke, or several unhalting strokes, across an entire set of the lifter plungers.

Abstract: A piston engine is provided in which adjacent cylinder pairs share a common combustion chamber and the pistons are mounted to reciprocate substantially in phase, one of the pistons in each piston pair receiving a rich mixture which is ignited by a sparkplug in that cylinder, with the other cylinder in the cylinder pair being passive in its preferred form, and receiving through a separate intake valve either pure air or a leaner mixture into which the combusted richer mixture pours, insuring that the greatest combustion possible resulting in the greatest percentage of carbon dioxide formation as opposed to carbon monoxide is created.