Evolution Hydraulic Roller Lifters with Hydraulic Cartridge Technology (HCT) are a revolutionary patented tappet. Not just an Original Equipment replacement they are an all-new bespoke design started from a blank canvas developed specifically by COMP Cams to meet the demanding performance and durability our customers desire for their modern and performance street engines. The HCT and proprietary manufacturing processes of these lifters ensure precision and longevity that exceed any lifter on the market.A combination of a self-contained drop-in hydraulic cartridge within a thick-wall lifter body and accompanying reduced oil volume less affected by aeration delivers the most consistent bleed rates between each lifter. The smaller volume within the hydraulic cartridge creates one of the most responsive and quietest lifters on the market today. Startup noise is greatly reduced and a precision-controlled bleed-down rate ensures excellent performance at high RPM. The cartridge design also allows for an incredibly stiff lifter body greatly reducing body distortion and further ensuring consistent hydraulic performance. Other features include increased duration and lift to the camshaft and two oiling features. Another industry first the hydraulic element of this patented lifter is serviceable allowing anyone to rebuild lifters in their garage.This set of Evolution hydraulic roller lifters for Holden engines features a seat height of 2.63 inches and 0.125 inches of travel with needle-bearing wheels.