this is what crane cams says about synthetic, which is neither too thin or not enough additive.
This is copied and pasted from an email sent
to crane cams
(Hello,
Yes, synthetic oils do not provide the proper interface between the parts that are attempting break-in.
Flat tappets for instance, do not get the traction needed to initiate the spin necessary for proper break-in.
Thanks,)
THAT is why you don't use synthetic to break in a cam it is too slick. this is merely my theory, but I also believe this is one of the basic reasons they went to roller cams in so many of the new engines, not to mention the fuel consumption.
as far as film thickness, the new modular ford (mustangs) have their main bearing clearances at a target of .0003-.0005 that is a half a thousands or less, there is an IRL engine (I don't know which one, the article did not mention it), has the clearance at zero. in this case most likely only a synthetic would provide adequate film strength.
I do know that I work in a heavy industrial atmosphere, and we use lots of gearboxes of varying sizes, and some of the manufacturers of course give the torque rating that can be put through their boxes, with the note that says you can safely increase the torque rating 25% if you use synthetic oil.
as you read in the article the zinc levels are at the level that started all this in the first place. even back then you used a break in lube. There is nothing new here. And given the fellas credentials I tend to believe his version of the story, since he was/is one of the people who actually conduct these tests for our beloved GM (I say OUR beloved, because don't we still own half of GM or some nonsense like that?)
