A few further thoughts on oils and ZDDP and cam to tappet wear , I hope people dont find the detail boring
cnavarrow appears to be a Porsche engine builder who has done some testing of oils on Porsche enngines he builds. The data I can see is pretty generic and does not adequately address the many aspect that affect engine wear and in particular boundary lubrication wear of sliding hardened metal on metal surfaces such as cams and followers where ZDDP is helpful. Also since he appears to be building modified and race engines the components, tolerances and loads will be different from road engines and without these sorts of details on the engines being tested any conclusions drawn about good versus bad oils and levels of ZDDP required can be very misleading.
There are many modern flat tappet engines made today that run happily on todays oils. For example my Toyota Landcruiser has 400,000kms now with no cam or tappet wear using what ever was the current oil was over the last 20 years.
The things that prevent cam to follower wear, which is what you are worried about when talking ZDDP levels in a twin cam are as follows in order of importance in my mind.
1. Cast iron to cast iron materials are better than cast iron to steel and both much better than steel on steel in sliding wear. If running a steel cam on a steel follower you need a 10 Rc different in hardness between the two components if possible to help to prevent galling and scuffing wear. Many racing engines using after market components use steel components as cheaper and easier than cast iron in small production runs, unfortunately the makers are often lax about their hardness levels or surface finish achieved
2. Ensuring the surface contact loads are not excessive. Heavy valve springs and high revs and aggressive cam ramp profiles increase the loads making wear worse in racing engines. For a twin cam keep the nose load under 200 lbs and keep the valve train as light as possible with lightweight steel followers, and titanium retainers and your Ok for 9000rpm +
3. Run in the engine properly to allow the cam lobes and follower to polish together. If changing a cam or followers its best to change both the cam and followers as a set and dont use a new cam with old followers or an old cam with new followers unless you get them checked and ground back to the correct profile and surface finish. Use a proper running in oil with the correct high levels of ZDDP which stops galling and scuffing during the critical run in period. Phosphate treating steel components or DLC ( Diamond Like Coating) treating steel components also helps during run in especially in if your pushing the nose load limits
4. Finally you get to the normal operating oil. A higher ZDDP level in the 1000 to 16000 ppm range does not hurt but the lower levels in modern oils do not appear to be an issue in a standard or most modified twin cam or most modern DOHC flat tappet vertical engines if the above three points are followed. My main concern with the oil I use is its temperature stability not its ZDDP level as the oil gets very hot as the oil is sheared between the bearing surfaces and a good quality Group 4 or Group 5 base stock oil retains its properties better in these conditions.
The reported issues that have driven the marketing craze for high ZDDP levels appear to be with engines with poorer tappet lubrication , typically where its inverted as in American V8's or push rod engines and on its side like a Porsche engine. I have not seen any credible reports of wear issues on properly built vertical DOHC flat tappet engines, but would be interested to see any if they exist. Also most of the reports of problems I have read come from modified engine builders where the adherence to the first 3 critical factors is not probably achieved by some.
cheers
Rohan