ZDDPPlus ZDDP Engine Oil Additive Zinc & Phosphorus 2 Bottles PROTECT YOUR ENGINE - Older cars with flat tapped lifters-cam need the added zinc for protection EASY TO USE - Simply empty entire 4oz contents of the bottle to a 4 to 6 quart oil change. PREVENT METAL ON METAL CONTACT - ZDDPlus alters characteristics to prevent metal on metal contact FOR USE ON PRE 1989 AND HIGH PERFORMANCE ENGINES COMPATIBLE WITH SYNTHETIC AND CONVENTIONAL MOTOR OILS