Safe, proven ZDDP EP agent takes the worry out of using new oil formulas in classic engines Restores ZDDP to the optimum level which existed when your classic car was designed Turns modern SM quality oil into the ideal oil for older cars, trucks, tractors, motorcycles, boats, etc. Compatible with ALL high-quality oils, standard or synthetic. Reduces cam and lifter wear in high-performance flat-tappet engines compared to a SM rated oil One 4 oz. bottle of ZDDPlus per oil change. You actually may be doing damage to the engine in your classic everytime you change the oil. If your car has a pre-1988, pre-ODB, flat tappet design engine, the "SM" oils now available lack one key ingredient - ZDDP. ZDDP was added to the type "SF" oils of those days and what it is is a surface modifier that prevents surface to surface contact. It prevents the tendency of parts to scuff and gall under heavy loads. This item is only needed in older, flat tappet design engines. This 4 oz. jar is all that you need to add to your oil the next time you change it to provide the necessary surface to surface protection it needs.