This simple but effective kit consists of four machined, heat treated and ground spacers that reduce the travel of the hydraulic unit in high RPM situations, thereby eliminating potential collapse of the lifter and its effect on cam timing. Under normal conditions, they allow tappets to operate as designed, resulting in low valve train maintenance and quiet operation. At high rpm, they simulate a solid lifter for increased valve train stability. Travel Limiters also aid cold starting by limiting tappet bleed-down, which narrows cam timing and increases cranking compression. Set of 4; requires adjustable pushrods.