Original Rhoads Variable Duration Lifters became famous for increasing low-end torque, engine vacuum and idle quality on engines equipped with performance hydraulic cams, while maintaining maximum top-end power. Many satisfied customers also reported better fuel economy and improved emissions quality, allowing them to pass emissions testing when they otherwise would have failed. Original Rhoads Lifters reduce lift and duration at idle by approximately .010" to .020". Duration is reduced by approximately 10 to 15 degrees. Total lift and duration are restored at approximately 3500 rpm. Typical vacuum increases range between 1 to 3 inches.  They can be used with both adjustable and non-adjustable rocker arms.  Since they are not non-collapsible or fully adjustable like the V-Pro design, the V-Pro design is recommended instead of the Original for all street applications with adjustable rocker arms.  Their legendary ticking at idle make them sound similar to solid lifters.  The Super Lube Groove Option is highly recommended for better lubrication and longer cam and lifter life.