Who has used one and what brand is the best out there?

 

I use Milodon p/n 16285 - works great on my '72 350 - note the length of your pump to be sure you buy a correct replacement for your pulley alignment. For this one - Notes: 6.000 in. water pump length

https://www.summitracing.com/parts/MIL-16285

 

Thank you.

 

There's only two options if you have a 6" pump: Milodon and Flowkooler. Milodon appears to still be using the very early design where they take a stock pump and just weld a plate on the back of the impeller. You generally have to use 2 gaskets to get some space between that plate and the timing cover. Flowkooler used this design initially also.
The Flowkooler pumps are also just stock pumps but with an aluminum impeller with many small non-directional blades.
Flowkooler is also available in shorter lengths.
Is it really worthwhile? Probably not. Increasing flow from a pump is unlikely to actually change cooling performance, especially if you're running a stock style thermostat.

I'd recommend just getting the GMB aluminum stock replacement. Bearings and seals still fail regardless of how much you spend - they're all coming from the same factory - so might as well keep it reasonable to replace.
Or, buy the fancy pump once then swap out the impeller on your replacement pumps. A little bit of heat from a propane torch is enough for the impellers to slide right off and on.

 

Do you have thoughts on the ideal space between the impeller and the timing cover? I have heard around 1/10" from the Pontiac folks that have to adjust their covers....

 

Thank you.

 

I used the old style Flowkooler pump. Honestly didn't do anything. The impeller is farther away from the pump wall than a factory closed impeller water pumps. I am currently using the new style reverse rotation Flowkooler water pump. The impeller is definitely an improvement over the riveted plate. Whether it actually helps with cooling is hard to say.

 

Just wherever it can sit where it doesn't hit the timing cover and doesn't hit the pump body.
Sure, for best flow and minimum cavitation there should be a specific spacing, but this is beyond even splitting hairs. Swatting flies with a hammer. Whatever metaphor works for you, but that's going waaaay down the rabbit hole to worry about water pump impeller spacing.

The factory cast impeller is almost assuredly the best impeller but they're not falling off trees. The riveted plate impeller was a real hack and thankfully I don't think that design was used very long. Heh, I forgot about that.