What you want in a Break-In oil is high levels of Anti-Wear chemistry but NO friction reducers so the asperities shave each other off, and still provide AW protection from too thin an oil film at the hotspots. Flattening out the asperities during run-in means more surface area for eventual ring/cylinder-wall sealing. You also need AW protection for the cam surfaces as the valve train loosen up a bit.
Originally Posted by burla
This is a great thread, as zinc both encourages wear and discourages it. Would it not be better to have nothing in the oil for break it? I like the idea, but I think it would take some pretty fancy testing above my pay grade to answer the question.