Joe hit the nail on the head...."once the cam has been polished to the lifter it is not as critical to have as much zinc as a new cam needs." It's that first 60 seconds where the zinc/phosphorus content plays a critical role in properly seating the cam-to-lifter surface. The surface of the lobe is hardened just "skin-deep" and the thought of reducing the life of the cam/lifter to save a few bucks just doesn't make sense to me.
On my 1960 235 engine with stock spring pressures I add 2 ounces of GM EOS to a full oil change after using the 1800 ppm oil for the initial run-in. I currently have 13K on the engine and my $9.00 oil analysis comes back A-okay!!! Pretty cheap insurance against catastrophic engine failure.
Dave
