Interesting Thread. I have always drilled the "steam holes" although as was said above that is probably a misnomer. As long as the water temp
in the area does not exceed the boiling point of the coolant mix at the rad cap pressure, there will not be steam there or anywhere else. But I remember reading about some Smokey Unick research on Y's when he ran them in '57. He found significant temp differences in various locations of the water jackets and there could be local boiling which would not show up in the temp gauge. It may be that Ford found this also with research and specified the holes as a fix. Because Ford would be using clean blocks and coolant the holes would not be crudded up.
My guess is that the boiling and overheating takes place primarly when the engine is shut down hot and water circulation is only thermo syphon. Then the holes would pass water to the area between the ex valves where the heat would build up quickly, cooling that area.
BTW Ted mentions another interesting Y design feature that has a little bit of unintended concequences. Since the the temp probe is located in the back of the head near where a large part of the water flow from the rad comes up from the block, the water exiting the head is likely to be some what hotter.
I don't know if it helped or not but I have a magazine picture of Doane Spenser's T bird motor that has beautiful water manifolds the take water from the back and front of the heads.
Doug T
The Highlands, Louisville, Ky.
