Should the 340/a/c have 6 or 8 blades on the impeller? The one I took off has 6 but it's red and I can't be sure it's original on my 69? The replacement one has 8 blades. I know on big blocks, maximum cooling systems have 6 blades. It's something to do with moving the coolant slower it faster to get the optimum rate of flow. I was going to use a Flowkooler pump but the a/c bracket will not clear the extra bulge on the top of the pump for the optional location for a mechanical sending unit

If your not concerened about originality, and have some extra $$$, buy the edelbrock water pump. The vanes have significantly more surface area than any of the oem style pumps.

I already got a stock replacement but I'm worried it's not good enough because it has 8 blades?

Some good information here on this recent topic..

https://board.moparts.org/ubbthreads/show...e=7#Post6859223

The 1969 factory service manual says on page 7-4, "When replacing the water pump do not install a standard water pump on any air conditioned vehicle or vice versa. See specifications for proper pump."

Specifications for 340:

WATER PUMP IMPELLER
Diameter-Number of Blades
Standard.................4.38"-8
A/C.........................3.50"-6

My one owner '69 340 with A/C has the original 6.5" dia fan pulley. The water pump was replaced several times with after markets, but I now have an NOS 6-blade pump with casting number 2863067, although I'm not 100% sure that is the right casting number for '69 production.

If your original pump has a casting number, it might be original or rebuilt from an original core. If no casting number, it was probably after market cast in Brazil or similar.

You can have your water pump rebuilt with the old impeller. For rebuilders, see Hemmings Motor News. Last time I checked with parts stores like Auto Zone and NAPA a few years ago, they were all selling these water pumps only with the non-A/C impellers.

You should not attempt to use a later year Mopar aluminum water pump, as these are a totally different design with the exit nozzle on the opposite side from the cast iron one.

That's what I thought. Thanks for the input

For what it's worth, here is a photo of my original pump along side the new GMB pump... There is a big difference in the impeller diameter, but note the vanes are about the same length. I installed it with a 180 deg. thermostat and the car runs consistanly very cool, just over the first notch of the temperature gauge. The literature with the pump said it had an improved impeller design.