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 Gas Gas EC450F 13-15 YZ450F 03-09 WR450F 03-20 YFZ450 04-08 YFZ450R 09-15 (Heavy Duty Springs Reccommended) Stainless Steel Forged One Piece Construction Black Nitride Coating Allows A Higher Resistance To Wear Along With Reducing Friction