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Old 19-11-2009, 07:19 AM
69coupe 69coupe is offline
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Pulley sizes ?

Can someone please give me the correct crank and water pump pulley diameters for a BBC . Was told by Norm at Aussie Desert Cooler that my water pump is not working hard enough due to wrong pulley sizes. I have after market ally versions and need to check the sizes. I guess I can either change the bottom pulley smaller or the water pump larger
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Old 19-11-2009, 08:18 AM
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Originally Posted by 69coupe View Post
Can someone please give me the correct crank and water pump pulley diameters for a BBC . Was told by Norm at Aussie Desert Cooler that my water pump is not working hard enough due to wrong pulley sizes. I have after market ally versions and need to check the sizes. I guess I can either change the bottom pulley smaller or the water pump larger
Water pump pulley is around 7", crank and water pump pulleys should nearly be touching.

Norm says

I can take a pic if you'd like
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Old 19-11-2009, 09:52 AM
69coupe 69coupe is offline
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Thanks Jim, a photo would be good. My water pump pulley is 6 1/4 " OD ( not in the groove). Maybe Norm is right ??

Where can you get a ally larger version ??
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Old 19-11-2009, 10:49 AM
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If yours is 6 1/4 it should already be spinning faster
I bought mine from Eagle a few years ago.

Why do you want it spinning faster?
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Old 19-11-2009, 12:38 PM
69coupe 69coupe is offline
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If yours is 6 1/4 it should already be spinning faster
I bought mine from Eagle a few years ago.

Why do you want it spinning faster?
Have been having cooling problems that is apparent only in this extreme heat. Went to see Norm and bought his twin fan "combo" unit that includes the shroud. Radiator is one of his " burnt out kings". When looking at my set up, Norm reckons the water pump is not working hard enough due to the daimeter of the pulleys,
After fitting the new fan set up its not really any better than the mechanical unit prevously. Looks neat
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Old 19-11-2009, 12:54 PM
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After fitting the new fan set up its not really any better than the mechanical unit prevously. Looks neat

He could sell ice to an eskimo............don't get me going on Norm.

Keep in mind that the faster you pump water into your engine, the less time it has to cool in the radiator

I have just come inside from setting the tappet on my mates Poncho, he is running a 509/560hp Merlin BBC and has a Race Rad and twin thermos. The fans where coming on at 205 and cooling it down 190 in this heat.....so me thinks you may have problems somewhere else

If it was at all possible i would have stayed with the manual fan....thermos are overated
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Old 19-11-2009, 04:41 PM
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Keep in mind that the faster you pump water into your engine, the less time it has to cool in the radiator
There are so many theories on this..
COLD water entering the block from a slow circulating pump isn't be good either.

But seriously with all theories aside..
All makes of American cars generally overdrive the waterpump by about 20-30%

The BBC GM pulleys that I have right here are:
Water Pump #3995631AO = 6.25"
Crank #3972180OE = 7.75"
..which is a 24% overdrive. GM's engineers (and the other makes) have had many years to do plenty of testing and math and that amount of OD is what works..
Unless you've got something completely abnormal, that should apply to just about anything us boneheads are doing. Works for me..

"I guess I can either change the bottom pulley smaller or the water pump larger "
Otherway around to speed up the pump.
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