Modern motor oils meeting API SL and specifically category SM do not contain enough zinc additive to assure proper anti-wear protection of high performance engines. The addition of Torco ZEP to any modern motor oil will put back the proper amount of Zinc Dialkyl-Dithiophosphate (ZDDP) purposely taken out to be catalytic converter friendly. ZEP coats all engine parts and won’t rub, scrape or scrub off and protects engines that are occasionally used from “dry starts”, a leading cause of premature engine wear of vehicles kept in storage. One 12oz. bottle treats 6 quarts or liters of motor oil.