StreetMax Chevrolet Mark IV, Gen 5/6 Mechanical Roller Lifters True street conditions call for on and off the throttle and long periods of idling. Those stop lights just keep getting longer. Most mechanical roller lifters were not designed for these conditions and will not last. Howards Cams StreetMax Mechanical Roller Lifters are specifically designed for this type of operation. Features CNC machined alloy bar stock bodies with case hardened 8620 rollers. Note: Designed for spring pressures up to 180 psi seat and 450 psi open. Made in the USA!