[cashflyer]

Well, I Googled to see what I could find. Apparently, the reduced ZDDP formulations are a problem with flat-tappet cams.

Hot Rod Magazine cites a few reasons, but reduced ZDDP seems to be high on the list.

And this write-up seems informative, too, citing info from Crane Cams, Castrol, and other sources.



Here's a chart showing the reduction in API approved levels over the past few rating changes.