ZDDP level vs TBN

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I have a question for the oil formulators out there... Last week I was looking at Eneos Sustina and their new ZP technology, which eliminates sulfur as a copmonent of the zinc additive chemistry. One of the benefits touted is that by eliminating sulfur, you eliminate the decomposition product sulfuric acid and therefore reduce the burden on an oil's TBN to neutrailze that decomposition product. This got me thinking... on typical oils with high levels of ZDDP, often they also have a higher TBN. On oils with reduced levels of ZDDP such as SM and SN xW-20 and xW-30, the TBN may not be as high initially. Is this intentional? Said another way, is reduced TBN a result of improved additive chemistry which do not rely as heavily on ZDDP? Moreover, the depletion vs retention parameters of TBN over time typically follow a pattern of rapidly depleting to some level, then flattening out and depleting very slowly for an extended period of time. Does this rapid initial depletion of TBN have anything to do with the sulfur/ZDDP content of the virgin oil? EDIT: Sorry, I probably should have posted this in the 'question of the day' section. Mods, feel free to move this thread.
 
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The reduced levels of ZDDP and related AW molecules that include phosphorus is all about maximizing Cat' life. The TBN level is suitable for the recommended OEM OCIs. I'm sure eliminating the sulfur component in the ZP molecule that Sustina uses does help minimize the formation of SO2 and therefore extend oil life but the only way to know how long an oil will remain serviceable for extended drain intervals is through UOA that measures both TBN and TAN. TBN alone is not enough.
 
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Reading this reminds me of RP HPS w synerlec. It's a sulfuric based ester with moderately high zddp. It also has a high TBN to boot which might contribute to poor TBN retention or something.
 
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Of course, you'll also see high ZDDP oils with decent levels of detergent and TBN (i.e. HDEOs, VR1). You'll also see dedicated race oils with even higher ZDDP levels, and TBN and detergency inappropriate for normal street use.
 
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