Max Effort AMC 199-258 / 4.0L Hydraulic Flat Tappet Lifters Designed specifically for higher revving applications. Perfect for race applications which require a hydraulic lifter or high performance street applications that need an extra edge. These lifters can show a noticeable increase of power from 5,000 rpm and up. Important: pre-load must be set at .002”-.004” (warm) to achieve performance levels. Made in the USA!