I completely disagree until proven otherwise. Any stock properly broken in flat-tappet motor with a stock cam and valvetrain which is properly broken in can use any of today's API SN engine oils, however...a flat tappet engine with any aftermarket valve train parts (more aggressive cam, higher pressure springs, higher ratio rockers, etc) could benefit with a oil with more ZDP in it. Look at GM'S engineering of the Corvette V8 and the maximum amount of pressure is 180,000PSI for max lobe/lifter interface. This was the rule of thumb for GM going back to the 50's. I am sorry but there is just too many stock GM V8' rolling around on bulk dino from the local 10 minute oil place with 200,000 miles still running strong and within originally factory specifications for me to buy that one. This shady tree mechanic talk of reduced ZDDP is killing stock engines by the thousands I am just not buying it. I am also saying this I see far too many pre 1980 vehicles that have close to 400K miles on them and often the vehicles are so "well" maintained the odometer does not work, the transmission is skipping gears, the interior is completely shot to you know what the engine start at every turn of the key and is preforming as close to new as a engine with 400K miles can. Each and every one has had the oil changed once or twice a year if that, more often than not once every 3-4 years and 30-40 years later are still running. If the OP wants to run a more aggressive set then I may see the benefit of higher ZDDP but I do not believe ZDDP is the ultimate anti corrosion or anti wear agent in a PCMO, but it is still a important one.
