There is a theory that new castings can be stress relieved by a temperature cycling....by several baking cycles. You can do this at home easily: (1) start the car, (2) let it warm up to operating temperature (3) turn it off, (4) let it cool down, (5) repeat a few hundred times.....my guess is that you have already done this. Such is why some racers start with a used block that has been temperature cycled. For a street motor (or for a budget build that is under $20,000) it is probably not necessary. Some folks call these "seasoned blocks"

mike in tucson