This is an intresting link, while i don't have a clue to the right answer on Zinc, i would challange any oil manfacturer to put their oil on a flat tappet cam .550 to .600 lift without zinc addative with 125/130 lbs of spring pressure in a racing application.
I agree that oil is more of a coolant than lubericant on the bearings it's a different story when it comes to cams and lifters.
The car manufacturers saw all this comming and changed to hydraulic roller lifters in the early 90's.
I know people running sprint cars that rules dictate flat tappets and the biggest problem they have is balancing spring pressure to make the cams and lifter survive and still run decent RPM's. I've seen flat tappet cams go bad on the startup with 125 lbs spring pressure, and the cam people all say not our problem.
I don't know how many people have seen the oil drained from a Nitro car or TF car, but it looks like it came from a mud hole.
On my end i don't run a vacuume pump, and there's alway some oil deluting with alcohol even with the best tune up and warm up. I gave up on the $8.00 to $12.00 a qt oil a few yrs ago and started useing shelf oil 20/50 and change it evry week between races. I do run lot's of clearance on rod and mains, .0025/.0035 and high volume pumps. I agree with Hammer on the oil pressure my oil pressure runs as low as 25/30 lbs on idle and almost never over 50 lbs at 7,000 rpms after everything is warmed to about 200 degrees. When i lived in Phx a number of yrs ago i knew a guy who ran a V6 dragster and only had 20/25 lbs oil pressure when i questioned him he told me oil pressure robs HP and he said it was never over 20 lbs in the traps, he did run mid 8's with the dragster. I haven't lost a bearing in yrs. but my cam went flat in my street El Camino afer an oil change last yr. in the 10 yr old enginge, and i rarly drove it.
O'h back in the old days when STP was king and they were sponsering Indy cars, they showed pit crews pouring in STP what they didn't show was the oil plug out and drain pan under the engine. :lol:
JMO
Zip.