I had the same thought as Tony on this. It is my understanding that the block stores heat requiring cooling passages to remove the heat. Less metal less heat. Moreover as you increase the size of the piston the distance to a water passage is diminished thus bored cylinders should cool more efficiently. However; the combustion volume is increasing apparently about 5% if the calculations on this thread are accurate so......Agree with Oly and Tony that structural integrity is a problem.
