[PontiacHO]

Been doing a lot of reading here regarding water pumps and divider plates.
I have a 1968 350 with the 8 bolt water pump and two plate setup.
The only replacement pumps I can find are the stamped steel impeller pumps. Supposedly the pumps with the preferred cast iron impellers aren’t made any longer. I have a new Gates pump with stamped impeller now and want to ensure the clearance between the impeller and rear plate is correct. What is the optimal distance? I assume bending the lip of the hole-opening towards the impeller with pliers and/or hammer is the process? Next-Butler Performance sells a billet impeller pump. Would that pump be a better solution and would there still need to be some bending of the plates to ensure efficient cooling?
Suggestions, guidance, leads, and criticism is appreciated.

[george kujanski]

The pump is manufactured by pressing the impeller onto the shaft. In the past apparently rebuilders and mfgrs have not been accurate (from a Pontiac functional POV) when they press on the impeller. Tweaking it by hand has worked for me and others apparently.
To answer your question, the proper dimension is to get the impeller as close as possible, In my case I settled on about .060, (1/16") without gasket. It started out at about .250 on my 11 bolt.

George

[chuckies76ta]

I like the stock cast impeller ones. You could take your old one and send it out to be rebuilt. I have two spares that I had rebuild couple years ago. Pretty sure there are companies still doing it.
https://www.cardone.com/rebuild-and-return/

[PontiacHO]

I found one at Ames. It’s ordered. I’ll also clearance the plate. Hammer and pliers?

[helmerrock]

An adjustable wrench closed over the sheet metal allows you to tweak to get the clearance where you want it. Patience helps.

[Formulas]

I use a hard faced (polyurethane) hammer what i do is sit in a chair put the plate down on the pump no gasket between my legs tap around the center plate hole patiently working the plate to the impeller get it as close as i can without touching the plate to the pump fins then put it all together,

you will have gasket thickness plus a bit for impeller clearance
not a bad place to be and you don't have to measure

[RocktimusPryme]

http://www.wallaceracing.com/water-pump-mods.php

This has a couple of helpful pictures. I used this when I clearanced my divider plate.

There are plenty of people here with much harder to cool engines than a 350 that are perfectly happy with stamped steel impellers so I wouldn't worry about it. You could always use a Flowcooler you are worried about it. Thats what I have.

[PontiacHO]

Thanks for the direction. Is 1968 the only year for two plates? So back plate opening bent towards impeller until almost touching? That almost seems restrictive but I’m ass backwards with all my processes!

[grandam1979]

I have a couple 68 pumps with cast impeller listed in the parts section for sale.

[lust4speed]

The testing and comparisons my friends and I have done has never shown the cast iron impeller to move coolant any better than the stamped steel impeller. Looking at them I give the edge to the cast item but in back to back swapping out water pumps we didn't notice any temperature difference. The funny thing is if you have seen one stamped impeller you have seen them all, but the cast impellers are all over the map with different blade count and blade depth.

I zero clearance the plate to the later pumps without a gasket in place and that has always given enough clearance when the gasket is added.

[MatthewKlein]

Originally Posted by PontiacHO

I assume bending the lip of the hole-opening towards the impeller with pliers and/or hammer is the process?

I used 3/4 drive sockets in the hydraulic press. Bent the center a little at a time.

[Squidward]

Personally I prefer an 11 bolt timing cover, doing as Lust4speed said, clearanced without gasket. I have 1967 accessories, but used to use an early 69 11 bolt pump to line up the water pump pulley. At some point those became tough to find.

I am only getting back into this game, but IIRC, there are a couple of late 69 water pump pulleys that allow use of the late 69+ water pumps with long nose to be used with earlier accessories. I ran into all of this when I stuck a late 69 350 into my 67 Firebird, and had to make water pump/alt/ps/ac all line up.

That might be an option. I don't care for the 8 bolt timing cover. Clearancing the two plates seemed a minor exercise in madness. Making a tasty fit of the divider to an 11 bolt pump was totally groovy.

[Half-Inch Stud]

I think all the centrifugal impellers of same diameter & area between vanes throw water to their ability with little regard to the plate gap. THIS BALD BOLD STATEMENT assumes 2 things.

The impeller vanes are curved in the correct direction. Straight is a basic case of correct. Primarily curve direction can decrease the required drive hp. Secondarily, the vane curve can bunch the fluid to spill the GAP, or it can throw the fluid to exit with much less regard to the gap. So i have seen some impelkers with the wrong curve (someone else posted such images here like 20 years ago).

To be "high volume" means the throw area between vanes need be high; advantage thin stamped steel impellers. Assuming the same diameter.

The gap is allowed. Zero gap is mechanically impossible despite a welded round plate on some impellers: there is still a back flow gap. So consider the fluid throw and consider the backflow gap, or the spillover gap. The optimal efficiency will be a small gap with a "don't care range around a numerical small gap.

Inefficiency can rise with twice that small gap yet that is on paper, and not a real issue due to the centrifuge elasticity of thrown fluid being able to pull the gap-fluid outward, for decent reversion isolation.

When the gap goes to about 4x the desired small gap then the reversion becomes annoying in the presence of pumping restriction downstream. So strive for the factory gap and it is double or 2.5x no biggie. beyond 2.5x becomes time to modify the gap.

There is a suction force causing the impeller to want to close the gap. If allowed the impeller will pull into the plate. Luckly the plate is so stiff, the pump besrings so tight in fore/aft that the gap bare changes "under load".

[PontiacHO]

I’m not smart enough to understand but thanks. I’ll close the gap to the closest possible gap. Hopefully that’s enough.

[tom s]

I have NEVER clearanced a pump,8 or 11.NEVER,just dumb luck I guess.Glad I have a 4 bolt on the 421SD,like 27 years now.FWIW,Tom

[lust4speed]

I've found that a medium sized ballpeen hammer using the flat works best for moving the metal, and just work around in a circle bringing the metal in. Last thing to do is to set the plate (or plates if 8-bolt) in place and spin the pump to make sure you didn't get carried away on the plate.

If the manufacturers didn't reduce the size of the impellers from what Pontiac used there wouldn't be a reason to check and set the plates to the new height. If you are having old pumps renewed with original pieces the clearance is probably where Pontiac wanted it. If you look and are dealing with a space between the impeller and plate that is 1/3 the length of the blades there is going to be cavitation and wasted energy. Couldn't find a pic of the aftermarket pump with the plate but did find some others. First is a totally stock impeller and plate out of a '62 421, and second pic is a stamped steel impeller on a stock plate. Neither of these need any work. The last pic is the stamped steel impeller with a "new and improved" PRW aluminum body water pump with the impeller cut down. That PRW needed plate fitment, and no idea why PRW decided to decrease both the diameter and height of the blades.

[PontiacHO]

Thanks for the narrative and photos. My plate does need some work. My pump from Ames is supposed to arrive Monday.

[Squidward]

Originally Posted by Half-Inch Stud

I think all the centrifugal impellers of same diameter & area between vanes throw water to their ability with little regard to the plate gap. THIS BALD BOLD STATEMENT assumes 2 things.

The impeller vanes are curved in the correct direction. Straight is a basic case of correct. Primarily curve direction can decrease the required drive hp. Secondarily, the vane curve can bunch the fluid to spill the GAP, or it can throw the fluid to exit with much less regard to the gap. So i have seen some impelkers with the wrong curve (someone else posted such images here like 20 years ago).

To be "high volume" means the throw area between vanes need be high; advantage thin stamped steel impellers. Assuming the same diameter.

The gap is allowed. Zero gap is mechanically impossible despite a welded round plate on some impellers: there is still a back flow gap. So consider the fluid throw and consider the backflow gap, or the spillover gap. The optimal efficiency will be a small gap with a "don't care range around a numerical small gap.

Inefficiency can rise with twice that small gap yet that is on paper, and not a real issue due to the centrifuge elasticity of thrown fluid being able to pull the gap-fluid outward, for decent reversion isolation.

When the gap goes to about 4x the desired small gap then the reversion becomes annoying in the presence of pumping restriction downstream. So strive for the factory gap and it is double or 2.5x no biggie. beyond 2.5x becomes time to modify the gap.

There is a suction force causing the impeller to want to close the gap. If allowed the impeller will pull into the plate. Luckly the plate is so stiff, the pump besrings so tight in fore/aft that the gap bare changes "under load".

Whoa. Trauma flashback to Heat Transfer and Fluid Flow module during my Navy training! HIS, that was pretty gnarly!

[OG68]

Originally Posted by Squidward

Whoa. Trauma flashback to Heat Transfer and Fluid Flow module during my Navy training! HIS, that was pretty gnarly!

I barely passed that class. A lot of mandatory night study hours got me through but didn't help with the Physics.
Back to the fleet...