What engine, cam, what car?
An old V8 + high zdp oil are not necessarily obvious bedfellows.
My current, modern Ford is a flat tappet (though OHC), and many Nissan's are flat tappet. Modern lowered phosphate oils are tested for API certification (EOLCS) using such an engine mockup
per ASTM D6891. Yes, spring open force is much less, but in OHC the lift is not leveraged so there is greater face velocity and acceleration at the tappet-to-cam contact zone.
If you are running a performance flat tappet cam with "stronger" open pressure to widen the RPM capability and prevent valvetrain float, then you may wish a higher % phosphorous - as old pushrod engines may have spotty lubrication at the cam and upper pushrod ball. Just know that it isn't a panacea, I have rebuilt many engines and most have had 2 or 3 lobes wiped in under 100K miles and a shot timing system.. An that was running with high zdp doped lubricants ( API SD/SE) and factory, light, valvesprings. The takeaway: oil wont crutch bad metallurgy.
IF you are running a high velocity cam profile, you have two choices:
1) Run a motor oil with suitable zdp doping
2) Add a break in lube from a top cam manufacturer
Mercury Marine Quicksilver 25w40 has high treatment rates, there may be others.
Then you have Various 4T Motorcycle/ATV oils from Valvoline, Castrol etc, many which have adequate doping but may be low on beneficial moly.
See here >
The additives in the oil sample is different to what Valvoline says they should be. Per the spec sheet, Zn/P should be 1120/1000 ppm, and Calcium/Sodium 1880/520 ppm.
bobistheoilguy.com
I prefer option #2 but many wish to trust a fully formulated product and not play
"mad scientist"
- Ken