So, there you have it! STP has got the goods. I don't use it because it effects viscosity... even though I don't think that is exactly a bad thing.
While STP would not say how much ZDDP is in their product, I did find a lab test that showed their various products have between 1 and 5% ZDDP. How they deal with the effects on catalytic converters, deposits and plug fouling from to much
zinc is beyond me.
I will just go with an
oil that already has it in the proper concentrations.