GM4-HDSS kit features ACT's most popular Heavy Duty pressure plate and most popular street disc. ACT Heavy Duty pressure plates use exclusive diaphragm design to increase clamp load, reduce deflection and maximize clutch life. All diaphragms endure a four-stage, heat-treating process for unparalleled performance. ACT pressure plates have precision cover stampings to provide rigidity and consistency. ACT's Performance Street discs feature premium organic materials with high copper content for better heat transfer and steel-backed lining for greater burst strength and durability. These discs have reduced marcel for faster shift action to complement ACT pressure plates, with increased strength and reliability.