A search on the subject will bring up a jillion items on the subject-the majority by individuals who are saying that syn is too slick to allow the rings to seat.
Then there are some that claim that GM, et al, do a good job of machining and syn works okay, but, your machine shop might not be as good as GM and therefore you should be using dino oil to be safe for anywhere from 250-1000 miles so the teeth left on the cylinder wall will be rolled over properly.
My feeling is that you should be using a machine shop that does a better job than GM does, but, we have all heard machine shop horror stories. I don't think there is much published factual data that goes one way or the other.
Economically, RK is right. If you do as I do, and change the oil after cam break in (flat tappet) and again, a few hundred miles later in order to cut the filter open and look for unwelcome shiny bits of metal, then using synthetic oil initially gets expensive. Might as well use something cheaper rather than spending $50 in the first few hundred miles.
As Porsche dynos their engines before installation, I wonder what oil they used for the dyno runs?
I have always liked Valvoline 20-50 Racing oil-in fact that is what I put in my GN the last go round because they did not have Mobil One in stock in 15-50 at the time. I have switched back and forth numerous times and cannot tell the difference other than I might have about 1# more oil pressure after several hard runs with the Valvoline.
<small>[ October 27, 2003, 11:40 AM: Message edited by: Steve Wood ]</small>
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