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How did you determine the recommended 0.12% Zn and P level (ZDP, a.k.a. ZDDP)?

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How did you determine the recommended 0.12% Zn and P level (ZDP, a.k.a. ZDDP)?

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There are many excellent SAE technical papers on the subject, but the one I found most interested was from 1977 titled “Cam and Lifter Wear as Affected by Engine Oil ZDP Concentration and Type.” There is some background that is needed to shed light on their results. First of all, there are different types of ZDPs. There is an Aryl ZDP which is the most stable form. There is also an Alkyl ZDP which although is not as stable, exhibits the best wear protection. In various fleet tests, it was determined that the best performance was from oils containting all Alkyl ZDPs or predominantly Alkyl ZDP blends. They also looked at the performance of “ashless” oils (0.03-0.05% Sulfated Ash) vs oils with normal levels (0.11% or higher) and it would appear that oils with lower ash levels needed more ZDP to provide the same level of protection. I bring this up since the newest CJ-4 and SM oils require significantly lower ash levels, less than 0.10%. Across the Indianapolis, Phoenix, and Los Angeles ta

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