Who makes the best water pump for the slant 6?

These days there is not that much difference between the aftermarket SL6 waterpumps.

The main things to watch for are the housing material and impeller design.
Housings came in cast iron or die-cast aluminum, all the aftermarket ones seem to be the aluminium ones.

Impellers were stamped steel or cast iron. Again, the stamped steel seems to be the only one offered today although I have seen 6 blade (most) and some 8 blade stamped steel impellers.

Impeller size is of the most concern, most are 3 1/4 inches in diameter.
The hole size in the separator plate is also a concern, most are 2 1/4.

Do some shopping around to see if you can find an 8 blade unit. (sometimes called an "HD" or "AC" pump)
DD

Thanks for the info. I know that we stay not very far from each other. Where would I find one of the 8 blade stamped steel impeller water pumps? Our what manufacturer should I look for?

The last 8 blade waterpump I bought was made by GMB, Japan. GMB also makes a lot of "low cost" U-joints and other replacement parts. I think I bought this 8 blade impeller waterpump at Kragens.

Here is a pic showing some of the different SL6 waterpumps.
Check-out the one modified for high RPM use, this racer trick cuts every other blade out of the impeller, to reduce drag.
DD

Wow, wouldn't that severely reduce the efficiency for not much power gain? Or is the gain more than I would think it is?

And what the hell is up with that round impeller up the top left???

_________________
'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

Most Slants will pick-up a tenth or more in the 1/4 if you pull-off the fan belt just before you make the pass.
DD

Is that with or without a fan?

Mitch

It does not matter, fact is that it is better to leave the fan on so when the fan belt is off, air blowing across the fan will turn it and circulate the water. This only works at freeway speeds but it does provide some circulation.
DD