what you are wanting to work out from your pictures above is known as a centrifugal pumps "velocity triangle" google it and be prepared for some math. Next you will need to determine the system flow losses, that can get pretty tricky to do theoretically. Real world measurement of pump flow and pressure is needed to determine the pumps efficiency.

This is exactly why I posted another thread asking engineers to please look at the information in this thread. I realize from prior experiences that this is beyond my level of understanding, so I need input from those that can digest this and offer a better understanding of it.

However (hopefully) it may not be necessary to do all the math and compute the velocity triangle in this case. I really only want to get a feel how the two basic impellers (original Fiat AC vs non-AC) compare in general terms - i.e. which one would move more fluid at a given RPM. Just looking at them I think the AC impeller does, but I know enough to not bank on casual observations and what I think.

it will come down to increased resistance to flow from some other restriction being the limiting factor

Excellent point, makes perfect sense. For now I'm going with the following assumptions:

1) Other aspects of the cooling system are being modified, which will likely change this to some degree.

2) It would be the same for both styles of impellers, so it is something of a constant factor having the same influence on both impeller options.

3) The factory used both impellers, so it might be fair to assume the total system is capable of handling either impeller effectively. In other words, the point of greatest resistance is sufficient for either impeller. So choosing the better (larger flow) of the two is best.

Perhaps one way to describe the goal here might be to find which combination of stock components (pump housing, pump impeller, pulley sizes, etc) will maximize the cooling system flow. Earlier Ulix stated his experience with using a electric pump made a significant difference -

finding the pump with the best flow is definitely worthwhile

Based on his findings with a

__much__ larger pump, it seems the remainder of the cooling system is sufficient to work with a greater pump volume/flow, providing a cooling benefit.