'609 vs '326 Water Pump

[Gregory G.]

What would make the two similar external looking pumps different internally?
The '326 is the later style pump, so does the cooling capacity provide better performance ?

Greg

[Mike E.]

Re: '609 vs '326 Water Pump

I believe that the upper fitting opening on the 326 is a larger diameter than the same opening for the 609. That would necessitate an adapter, which is a point loss for judging purposes, and an eyesore to anyone used to looking at a 62 for correct configuration. I don't believe that the cooling capacity would be significantly affected by one or the other.

[Joe L.]

Re: '609 vs '326 Water Pump

Greg-----

No, they're functionally the same. While there are some minor differences between the castings, the main difference is the size of the upper boss for the external bypass. The '609' was designed for a 1/2" NPT thread. The '326' was designed to allow larger fittings.

By the way, the non-external bypass counterpart of the 3782609, known as GM #3782608 and originally released at about the same time, was used right through the 1970 model year (69 and 70 for Corvettes only).

[Jack H.]

Re: '609 vs '326 Water Pump

Mike, drilling and tapping the upper boss for the external bypass elbow was a secondary operation that turned a given casting number into a finished part number (along with stuffing the shaft, impeller, pressing the hub and installing the rear plate). You'll find '326 castings with both the small hole (1/2-inch NPT) used by Corvette and Camaro as well as with the large hole (3/4-inch NPT) which were commonly used in other engine applications including truck.

In water pump land, we seem to know and agree on the '609 and '326 pump housing castings being used on Corvette, but there's an intermediate casting number (175) that doesn't get much discussion. Joe Lucia has mentioned it in other threads, but the JG books simply don't talk much about it.

The full casting number falls numerically between the '609 and '326, as if it were the 'missing link' between the two pump housings. Further, when you lay all three castings side by side, you can easily see the design progression!

The upper boss on the '609 is very small and I'd venture to say it could NOT have been drilled and tapped for a 3/4-inch NPT bypass nipple. It doesn't look like there's enough material...

The '175 casting has a larger upper boss that can easily take either a 1/2 or 34 inch bore, but the extra material interferes with a deep pulley and the boss has a 'flat' cast into the front side of the boss to provide clearance.

The '326 casting has an even larger upper boss (maybe 1/8-inch fatter in circumference). It also has a 'flat' cast into the front side of the boss for pulley clearance and the flat is visibly larger/wider.

I think guys like Bill Mock believe there was a natural transition over time with the three castings (609 -> 175 -> 326), but we at NCRS don't seem to recognize the '175 casting which sure looks like the missing link once you lay all three side by side...