First off, I would like to state that I am not an engineer, nor do I have a lot of knowledge on oils.......but I have done some research and have formed my own opinion from this research.
First off, the new ILSAC GF-5 and the API Specifications require that Phosphorus be held to the reduced amount from the last spec. They claim that these new oils are backwards compatible and provide adequate protection for sliding friction such as that on a flat tappet cam. We have all heard however that at least on some engines that this may not be true........so we all run out and buy additives to put in the oil and protect our engines from premature cam wear. It is my belief that this works......adding ZDDP for additional zinc and phosphorus probably works.
My understanding of the ZDDP is that it helps modify the wear characteristics of the oil under sliding contact....... It essentially is a band aid for less than perfect oil base stock. So if we buy good oil.......with high quality base stock, do we need the ZDDP at all? I believe there is oil that does meet our needs without the ZDDP and all you have to do is look for oil that meets a slightly different standard.
Here is a link to the ILSAC GF-5, API SN Standard:
http://www.infineum.com/SiteCollectionDocuments/notebooks/gf5/FinalApprovedSpec.pdf
If you look down the page you will find the spec for average cam wear....which is 60 PPM.
Here is a link to the old ILSAC GF-1 Spec, which would have covered API SG oils......and they were OK for a flat tappet cam:
http://www.swri.org/4org/d08/Abstracts/GasEng.pdf
If you read down the test, you will find that the average cam wear spec for GF-1 was 30 ppm or exactly 1/2 the level of the new GF-5. It is my opinion that this reduction in the standard is the reason the we might suffer premature cam wear in our older engines. Not the loss of zinc and phosphorus, but the higher wear is the cause of the problem. The ZDDP is added to reduce this wear.
So getting back to my point that all we need to do is to find an oil that is more restrictive on allowed cam wear and we may not have to add ZDDP additive.....but how do we find such an oil? Simply we look at European spec oils.
ACEA oils are oils that meet the requirements of the European Automobile Manufacturers Association. What makes these oils better for flat tappet cams......quite simply the wear requirements for these oils are much more stringent than ILSAC/API oils.
Here is a link to ACEA oil requirements:
http://www.acea.be/images/uploads/files/2010_ACEA_Oil_Sequences.pdf
Reading the spec, you will find that the average cam wear requirement to pass this spec is 10 ppm or less. This wear requirement is 1/3 the limit of the old ILSAC GF-1 that was good for our older engines. In other words, the older GF-1, which our engines liked, allowed 3 times the amount of cam wear as the ACEA specs allow.
ACEA oil can be found at any Walmart too.....
Here is a link to Mobile 1 Extended Performance 5W30 spec sheet:
Mobil 1 Extended Performance 5W-30 Advanced Full Synthetic Motor Oil
It meets the standards of ACEA A1/B1 A5/B5, so it should give better protection from cam wear than the older API SG oils, which were good for flat tappet cams. There are others to, but this is the first that comes to mind for me. All you have to do is look for the ACEA ratings.
I only present this to give another look at oils from a different perspective. This is not meant to change anyone's mind about ZDDP, nor will I spend any time arguing about this......it is just another view point on the problem of getting good oil for a flat tappet cam engine. I hope some of you read this and use the information to educate your self and come to you own conclusions.
Again, I do not believe it is wrong to add zinc and phosphorus to oil to reduce cam wear. This works.....but for me, I choose to buy a quality base stock and not have to add anything........
FWIW.....