I do business with several
oil companies here in Houston and the few engineers I have spoken to agree with Jim above that 1200-1400 is plenty and beyond that there could be corrosion issues. I am running Valvoline VR-1 straight 40 in my new flat tappet S/O and it has 1400 ppm of
zinc.
Patrick, you note that your engine has 4k miles now, did you happen to do a Blackstone when it was right off the dyno for comparison?