It seems that zinc is only important during camshaft break-in on a flat tappet engine. Once that original wear pattern is established, the zinc concentration becomes much less important. The retailers of "high zinc content" oil have found a good way to pick the pockets of gullible people, I think! It's sort of like the folks who tout other "mouse milk" oil additives like STP, etc. I attended a seminar several years ago hosted by a research chemist for Kendall Oil Co. and the question was asked about "additives". His answer went something like this: "We use 22 additives already- - - -17 of them are beneficial to your engine, and the other five offset the bad effects of those 17! That's good enough for me!
Jerry
