Hi Pishta. Thank you for your response. I am not much of a mechanic, so I am sorry that I do not know the difference between open and closed chambers. I will say that the heads have a bit of a recess where the valves will open and close. These are stock 273 2bbl heads from a 1966 Dodge Dart. I will do what you described for a test. Also, I do not know if this block has ever been decked before, but, after I removed the heads, during dis-assembly, I turned the crank, and the pistons did not reach the top of the block deck. All eight were slightly below the deck. Thank you for your time. Old Dart 66