Water Pump Pulley Question

[FY1Cuda]

Trying to mock up a Vintage Air system on a 383.  We had a 6 7/8" water pump pulley on the car, but that won't allow for the correct placement for the V-belts.  I found a smaller pulley (5 3/8") in a parts box that lines up nicely.  What is the correct diameter for a big-block water pump pulley for a car with AC?

[Chryco Psycho]

the smaller pulley will turn the pump faster , no harm in that

[cudabob496]

the smaller pulley will turn the pump faster , no harm in that

might cause damaging cavitation. To compensate, would need a smaller crank pulley.

[HP_Cuda]

I received one of my cars with the smaller pulley which I replaced about 5 months ago, it worked fine but he also used a HV water pump which was a bit crazy. My old time Mopar mechanic of 35 years told me it must have come off a small block.

Overall, the Cuda needed more cores to cool it down. Now it doesn't budge at all.

[FY1Cuda]

Thanks for the input.  I chickened out and got a 5 7/8" double-groove pulley from Bouchillon.  It's supposed to be correct for a big-block AC car.

[mopar jack]

The smaller pulley is probably what the factory used on A.C. cars. My 71 factory service manual list the pulleys as a ratio of fan to crankshaft. So on A.C. cars the fan to crank ratio is 1.4:1 and a non A.C. ratio as .95:1

[Chryco Psycho]

The AC pulley is definatly smaller but I have nothing to refer to for measurements

[Denison636]

I am also curious what kind of r.p.m.'s a factory a.c. Compressor can take.
Not meaning to high jack the thread but curious due to I got a 340 that I turn over 6,000 a lot. I also been know to take it up to 7500 if it is to win a race.

[cudabob496]

I am also curious what kind of r.p.m.'s a factory a.c. Compressor can take.
Not meaning to high jack the thread but curious due to I got a 340 that I turn over 6,000 a lot. I also been know to take it up to 7500 if it is to win a race.

If AC not on, compressor should not be engaged?

[Denison636]

Thanks, I forgot what that clutch did. Just had a major brain fart that fog the glasses is all.

[cudabob496]

Thanks, I forgot what that clutch did. Just had a major brain fart that fog the glasses is all.

No prob, if was ingaged at high rpm, might get very cold in the car! haha

[brads70]

I've been researching pulley ratio's as I'm still having cooling issues at idle /low RPM's . Chevy/Ford have ratio's of 1.23 or so. Mopars don't? They have less so it seems? I'm wondering why?  Engineers designed them for power over cooling? I have A/C pulleys on my car crank is 7" water pump is 6.2 ( measured on the outside diameter)  so that calculates to 1.129 ( 7 divided by 6.2= 1.129)
I was considering  machining my own water pump pulley ,speeding up the water pump/fan to a 1.2 ratio or more (1.3 maybe?)? So in my case that's a 5.8" -5.5"water pump pulley.   In my case max RPM  the rev limiter is set at 6000rpm's  so with a 1.2 ratio @ 6000RPM's the fan will be going 7200-7800 RPM's which should be fine.
Thoughts? 

[cudabob496]

I've been researching pulley ratio's as I'm still having cooling issues at idle /low RPM's . Chevy/Ford have ratio's of 1.23 or so. Mopars don't? They have less so it seems? I'm wondering why?  Engineers designed them for power over cooling? I have A/C pulleys on my car crank is 7" water pump is 6.2 ( measured on the outside diameter)  so that calculates to 1.129 ( 7 divided by 6.2= 1.129)
I was considering  machining my own water pump pulley ,speeding up the water pump/fan to a 1.2 ratio or more (1.3 maybe?)? So in my case that's a 5.8" -5.5"water pump pulley.   In my case max RPM  the rev limiter is set at 6000rpm's  so with a 1.2 ratio @ 6000RPM's the fan will be going 7200-7800 RPM's which should be fine.
Thoughts?

some water pumps are probably more efficient at low rpms than others. I just raise my idle speed.