"Excellence in Performance", backed by the best one-year warranty in the industry! XACT Flywheel Prolite Dramatically improved engine response and acceleration, mild to moderate gear rattle; Heat-treated forging for strength and toughness, induction-hardened ring gears for maximum life; One piece construction allows less opportunity for failure and provides uniform efficient heat transfer from the clutch disc. No more warped inserts or loose ring gears; Recommended for race use; Forged, CNC machined and dynamically computer balanced for smooth high RPM reliability 600390 is a Prolite flywheel, which is ACT's lighter flywheel offering with lowest inertia. Prolite flywheels are designed for best throttle response and acceleration. Prolite flywheels are preferred for road racing or rally racing, and have reduced drivability. Materials are properly distributed for maximum strength, good heat tolerance and rigidity. ACT flywheels are serviceable and can be resurfaced with no need to purchase additional parts.