Rhoads Original hydraulic flat tappet variable duration lifters are famous for increasing low-end torque, engine vacuum, and idle quality on engines equipped with performance hydraulic cams, while maintaining maximum top-end power. Better fuel economy and improved emissions quality are often reported by customers with Rhoads lifters. The unique construction of Rhoads Original hydraulic lifters reduces lift and duration at idle by approximately .010 in. to .020 in. Duration is reduced by approximately 10 to 15 degrees. Total lift and duration are restored at approximately 3,500 rpm. Original Rhoads lifters are also anti-pump-up for higher rpm revs. Typical vacuum increases range between 1 and 3 in. Rhoads lifters can be used with either adjustable or non-adjustable valvetrains. Original Rhoads lifters, with their legendary "ticking" at idle, sound similar to solid lifters. These Rhoads Original series lifters are designed for use with high performance street, marine, or racing applications.