Open Chamber Heads vs Closed Chamber Heads....

Well a "Hemi" head is about as open a chamber as it gets, the poly head as well. As for closed chambers making power, take a look at an old Chevy 235. Plenty of quench, but absolutely diabolical for flow. Also, shallow open chambers have less surface area, which means less area for combustion heat to be absorbed into the head. The shape of LA head combustion chambers are more than a little bit a result of the valve angles. If the valves were more in line with the cylinder axis, the chambers could be shallower with less shrouding. But, the engine would be wider, rockers longer, the whole thing heavier and more expensive because it had more iron in it, etc. Remember the LA was a budget rework of the A engine so it would fit into economy cars and cost less in volume production than the poly. Since the chambers were on the large size to begin with, adding the quench pads was a cheap easy way to increase compression and still keep HC emission levels reasonable.