A vote for the cast impeller
 

I know this has been beat to death but this is my story and I'm sticking to it.

61 with the old four bolt pump. PO had overheating problems. Vapor locked (a vapor return line fixed that) but it would run 200-210 and it didn't take a very hot day to cause that. I pulled the 195 stat and put in a 185 which helped but I still like to be under 190. Added a shroud and clutch fan which still didn't get me where I wanted to be. A few years ago I had the engine out to get things cleaned up and looked at the pump but never really noted which one it was and quickly forgot. Cast or stamped impeller - I didn't remember.

So I picked up a rebuilt pump and put it in. Now it runs a nice 180-185 (still the 185 stat). Even on 90-95 degree days. Pull off the road and let the revs drop down in town and it will go to 195-200. But you expect that.

The pump I took out is on the left and the one I put in is on the right. Note that although the stamped impeller has more blades it is also a smaller OD which I think allows some loss of efficiency at the blade end. Can't say how the cast impellers with the shorter backward angle blades would perform.

Wow, great photo. That stamped POS will move a lot less water.

Just from a visual standpoint, the cast full vane impeller looks to be far superior design. The little sheet metal one seems to have many ways for the pumped fluid not to exit the pump cavity and just cavitate and create bubbles and turbulence. It would be fun to bolt those pumps to a clear plastic box, fill with water and watch them in action.

The only water pumps I've ever used on my Pontiacs had cast impellers. I never had overheating problem, either.

The new high flow that is being used on my 461.

Who makes that water pump, is it a Flowkooler? I have one of their water pumps in my car, but the water pump style used in the 1964 and earlier cars doesn't have an impeller like that.

Just ordered up a 4 hole'r from "Stone" Auto. Specifically ordered a reman as I didn't want one of those new POSes from China. What do they send me? A new Chinese one. Almost bright side is it has a cast impeller.

The trick it seems like when installing a new water pump on our Pontiacs is getting the right clearance between the pump and the plate between it and the timing cover. I think there was a thread about this a while ago, but it was determined by someone on this forum that too much clearance between that plate and the water pump impeller severely affected the cooling ability of the water pump. Or at least clearancing the plate (i.e. bending it just enough to maintain adequate clearance of a certain dimension around the impeller) improved cooling by quite a bit.

Don't know about the "later" 4 bolt pumps, but the '50s models didn't have a "plate". Just had the pump and the timing cover casting.

The plate came sometime after the switch from the four bolt pumps in 1963. Not sure if the plate came with the change or later.

694.1 - that pump looks a lot like the pictures I have seen of the cast impeller pump sold by NAPA. Maybe it is the same as I don't know about NAPAs supplier. Keep posted about the performance. I can't tell if the OD of the impeller is as large as the impeller I have or not. I can see a difference between my old stamped impeller and the cast one which I think has an effect of the performance. And maybe the lack of holes from the back side will affect it also.