Performance Hydraulic Roller Lifters: VThunder by COMP Cams, the leader in valve train technology, introduces their new replacement Evolution? Big Twin hydraulic roller lifter to its line of V-Twin aftermarket products. Our new lifter features a rigid nodular cast iron body with a 52100 bearing, axle and wheel assembly for strength. VThunder?s lifter utilizes an advanced ultra-high flow metering system which allows more oil movement through the engine to aid in cooling. Each lifter is precision I.D. Ground and matched with a Graded piston, and features a high performance retaining ring.