COMP Cams Evolution HCT (Hydraulic Cartridge Technology) is a new patented tappet. The Evolution HCT tappet provides most consistent performance of any set of lifters in the aftermarket. A combination of self-contained hydraulic cartridge and accompanying reduced oil volume that is less effected by oil 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. Startup noise is greatly reduced and a precision controlled bleed down rate ensure excellent performance at high RPM. The patented cartridge design also allows for an incredibly stiff lifter body