OEM Replacement Valves are manufactured to OEM specifications from SUH3HT Steel for added corrosion and oxidization resistance.Performance Valves feature a forged one-piece construction, nitride coating, modified radius, swirl polish, chromed stems, and stellite tips. This provides reduced friction for quicker/higher revs and a longer valve life. Heavy Duty Springs RecomendedExhaust RMX450 10-19 RMZ450 08-19 (Heavy Duty Springs Reccommended) Stainless Steel Forged One Piece Construction Black Nitride Coating Allows A Higher Resistance To Wear Along With Reducing Friction