Cooling/Charging & Pulley Ratios
 

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 %.

As mentioned on another thread speed and air volume passing through the radiator certainly has a lot to do with cooling. If a car were being driven at high speed constantly the water pump probably would not need to be over driven. Town driving, idling, and slow traffic will require the water to move faster to achieve the same cooling effect, consequently overdrive the pump.

Rick