A few other small items some of you are forgetting....... First of all, if the engine is already "broken-in" as in has a few thousand miles(or lots more) on it, The ZDDP requirements are a lot less than when you are breaking in a brand new engine. Also some other things to take into consideration, is, cylinder wall to piston clearances,ring tension/end gaps, bore concentricity, camshaft lift/duration and valve spring pressures on a flat tappet type of cam, not to mention the material all these items are made from. ALL of these play a large part in how much ZDDP you do or do not need to keep the engine alive.
Just tossing that out there as food for thought.
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