Thanks for the replies. If anyone else has access to any historical specs, API or manufacturers data sheets I would sure appreciate access to the info.
I have noticed that zinc / phosphorus ratio seems to vary and is not necessarily 1:1
I see SG was still in play 1989 and SH played out in 1996. The drop to 1000 ppm thereafter seems to correlate with the increase in flat tappet related failures. I really would like to know what it was before SG. We have speciality oils with 1500 ppm zinc (Brad Penn) and going back to 91 or so, Kendall GT was listed as high as 1600 ppm zinc. I wonder if the PCMO oils generally available before SG had much more, but maybe never as high as 1500 - 1600 ppm which seemed to be SOP for off the shelf racing oils.
Its mainly a historical interest. There is a lot of interest in one of the muscle car forums I belong too, because historically these are flat tappet cam engines of which many members have had one or more breaking in failure or just going flat (now after find out more facts about each event, some were self inflicted for various causes, but not all). Others with roller cams are obviously not having that problem. Much debate and angst over adding ZDDPlus to off the shelf SM oil and agony over how much zinc is too much. What do the industry experts here say? I did come across a SAE paper extract of a engineer from Ford who did find correlation with flat tappet cam failure with the current low zinc / phosphorus oils.
