The Stovebolt Site Forums The Shop Area Engine Shop Water Pump Adapter. Fantastic.

I've tried out Pre 68 Dave's adapter which raises the water pump on my '61 261 to the center of the radiator. Fantastic as most of you already know. It was 90+ today and it idled a long, long time. The water temperature went up to exactly 180 degrees (my thermostat's value) and stayed there.

With the previous stock 261 pump, I would have over heated for sure with maybe a vapor lock.

Glad it worked out for you!

I am curious what about this adapter plate makes the cooling better? Is the the fact you are moving the pump to the middle of the radiator or is the older pump a better design? It seems like the adapter plate would pull the impeller out of the existing 4" hole in the block and make is harder to pump the coolant.

The late water pump has far more capacity than the early pump. Its rated output is 14.5 GPM (gallons per minute) per 1,000 pump RPM, 72% higher than the early pump at 8.4 GPM.
Using the large late pulley will reduce water circulation significantly.

From my understanding people are replacing the stock 261 pump from their late (55-62) engines with an earlier pump when doing this conversion.

I have used this on my 1960 261 (in my 1954 Chevrolet Suburban).

I highly recommend this adapter it should be listed in a stovebolt hall-of-fame (for appropriate 235s and 261s).

Pumping more GPM doesn't necessarily mean it will cool better. Slower moving coolant allows more time for engine to transfer more heat to the coolant, then for the coolant to transfer more heat to the radiator. In addition, for those that are replacing their 216 and early 235's with later model 235-261's, the longer pump interferes with the radiator. You can resolved this issue by buying a short shaft water pump made specifically for this mod, shorting the pump yourself, or moving the radiator to the front of the support. None of these mods will center the pump on the radiator causing inefficient cooling. Some 'bolters have done this and attest to no cooling issues, but others have not been as lucky.

I have installed this adaptor on a '59 235 in my '52 Chevy 3100 and it works great.

My hats off to "Pre '68 Dave".

I bought the short shaft water pump a few years ago when I didn’t know any better. It works for me, although the truck will start to creep up to 200 ish when idling for long periods on a very hot day.

I have not put it to an extreme test, but I suspect that I might have trouble in a traffic jam.

When the time is right (other major engine work or swap), I will do the adapter plate with the earlier pump.

Pumping more GPM doesn't necessarily mean it will cool better

GM thought so

In racing engines they're pumping a barrel a minute through the engine at high RPM. Higher coolant velocity minimizes hot spots.

I'm using the low mount pump and a 16" 6-blade truck fan, the bottom blades of which extend below the radiator. I had to drop the radiator in the mounting hoop several inches so the fan would clear the lower radiator hose outlet. If I was a good sheetmetal man I'd make a shroud to fit. Instead I added a pusher fan in front of the radiator with a 205 degree-on switch from the Peterbilt dealer and a relay. On a long, hard pull on a hot day it will go over 200 degrees, otherwise runs at 180 per the thermostat.

Everybody is ignoring pulley diameters in this fire hydrant watering contest. The usual suspects are pontificating about theoretical stuff when it's an established fact that the conversion plate works, keeps the engine cool, and avoids having to do a bunch of modifications when using a later model engine in an early chassis designed for the high pump. It's also possible to machine the pressed-on pulley of the early pump and install a 2-sheave pulley for a Furd small block V8 to accommodate non-standard belt routing for power steering, air conditioning, etc.
Jerry

If you run the small pulley high-mount waterpump on a late 235 with it's factory crank pulley you are in danger of making a nice, clean slot in your hood when a fan blade comes off. My next-door neighbor did exactly that to his 51 car.

If I wasn't so far into my current setup I might consider the adapter plate setup. But the current setup works for me, keeps cool, drives the AC compressor, keeps the house battery for the camper charges and doesn't trash belts.