What is the purpose of steamholes?

 

collant passage

 

Assuming this is a 400 small block? There is no coolant passages between the cylinders so at the top of the cylinder between two of them there is pretty high heat and the coolant can boil and create a steam pocket, that's bad. Those small holes will keep enough coolant moving to prevent this. Pretty much a result of the maxed out bore size in this engine.

 

thanks