Thanks for the input on the stock pulley diameters.
Having that data and further digging helped me understand my low speed cooling situation.
1.Stock pulleys overdrive the water pump 10 % on average.
This what Stewart Componets has to say about pulley ratios.Griffin Radiator told me the same thing.
http://www.stewartcomponents.com/tec...ech_Tips_1.htm
2. The stock pulleys turn the alternator 2.5 - 3 times crankshaft pulley rpm.
When the alt. gets down to the 1.75 times range,idle-low speed charging is between little and none.
MARCH PULLEYS
V - BELT, 1969 1/2 & LATER 302 - 351 WINDSOR & CLEVELAND
STREET ROD RATIOS
5.5" CRANK
5.25 WATER PUMP 5% OVERDRIVEN
2 11/16 ALT. 2.05 TIMES CRANK RPM
PERFORMANCE RATIO
5.5" CRANK
6.25 WATER PUMP 12 % UNDERDRIVEN
2 11/16 ALT. 2.05 TIMES CRANK RPM
SERPENTINE BELT CONVERSION FROM V - BELT
STREET ROD RATIO
6 1/8" CRANK
5.5 WATER PUMP 11% OVERDRIVEN
2.5 ALT. 2.45 TIMES CRANK RPM
PERFORMANCE RATIO
4 3/8" CRANK
5.5 WATER PUMP 20 % UNDERDRIVEN
2.5 ALT. 1.75 TIMES CRANK RPM
1979 - 1993 5 LITER SERPENTINE PULLEYS
PERFORMANCE RATIO
4 3/8" CRANK
5.5 WATER PUMP 20 % UNDERDRIVEN
2 3/8 ALT. 1.84 TIMES CRANK RPM
POWER & AMP
STEEL & POWDERCOAT ALUMINUM
4 3/8" CRANK
5.5 WATER PUMP 20 % UNDERDRIVEN
1 11/16 ALT. 2.59 TIMES CRANK RPM
CLEARCOAT ALUMINUM
4 3/8" CRANK
5.5 WATER PUMP 20 % UNDERDRIVEN
2.0 ALT. 2.19 TIMES CRANK RPM
As you can see, some of these pulley sets cut the water pump output by
30 %.