We've had lots of discussions on the subject. Search for "zinc" or "ZDDP" and you'll get lots of reading. They pretty much all come to the conclusion that unless you have stiff valve springs and/or a high lift cam and are working the engine hard for extended periods it's not necessary. Modern oils are adequate. If you're breaking in a new camshaft that can be a horse of a different color. In that case follow the manufacturer's recommendations. I've got LOTS of miles on old Chevy sixes and have never added a drop of extra zinc.
Last edited by Tiny; 04/29/2021 11:51 PM.
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