Castrol GTX Classic is a high-performance engine oil for push-rod, flat tappet engines and performance cam applications. It?s specially formulated for classic/collector cars, muscle cars, hot rods and race cars. It?s high zinc and phosphorus content helps prevent premature aging, wear and metal fatigue on engines with high tension valve springs or performance modifications that create high contact pressure and extreme internal temperatures. Castrol Classic 20W-50 is suitable for use in automotive gasoline engines where the manufacturer recommends an API SJ or earlier specification 20W-50 lubricant. NOTE: NOT FOR USE IN MODERN ENGINES WITH CATALYTIC CONVERTERS OR WET CLUTCH APPLICATIONS Specialized additives containing high Zinc (1400 PPM Max) and Phosphorus for extreme wear protection Formulated to maintain tough and thick oil film even under severe conditions Minimal foaming and high resistance to thermal degradation Compatible with gasoline and alcohol-based fuels