Here it is!
http://www.gmhightechperformance.com...ild/index.html
"During the first several hundred miles of operation, the metal parts of the engine "mate" to each other. While advances in technology mean that engine parts are manufactured to more exacting tolerances than ever before, the microscopic uniqueness of any one piece of metal that comes off of the assembly line or out of a machinist's cylinder honing machine continues to endure...Happily, those days are ancient history, and thanks in part to this advance, no elaborate, "ceremonial" break-in is required for an LS1-based engine. But our beloved V-8s still have important parts like bearings--and most significantly, piston rings--that require a wear-in period to operate properly."
"The type of fluid used during break-in is also important. You may have heard that synthetics are "too good" to use during the first miles on a new engine, and this is true. The main reason for this is the piston rings, which as we have said need time to seat to the cylinder walls properly; if they don't, horsepower and efficiency will be left on the table thanks to reduced cylinder pressures. Mark Chacon elaborates: "The ring face must have ample time to break in to the cylinder wall finish, and running a conventional oil for the first 1,500 miles or so will aid this. Ring seal needs to be firmly established before synthetic is introduced into the motor, and one of the reasons the factory LS1 has such a heck of a time with ring seal to begin with, in my view, is that many come from the factory with synthetic oil in them. Once you put synthetic in, what you've got is what you've got, and the rings may never really wear to the cylinder walls. Of course, feel free to eventually switch to synthetic because of its better properties, but make sure the rings have seated fully first; short of using a cylinder leakdown tester, mileage accumulation is the only way to tell whether this has occurred."