Originally Posted by mrc013
I am installing a 5.7 Vortec stroker in the 41 Chevy. I am using the serpentine set up with a REFVERSE FLOW PUMP. I noticed the block, where the water pump mounts, ....has the lower hole on the passenger side blocked off. Why?
The original clockwise rotation pump tends to favor volume output on the passenger side of the block. The small hole is intended to be a bleed back to the intake side of the pump to balance up the flow to that of the dirvers side. It's really too small to be effective at engine speeds beyond cruise so it never provided the help where such a flow difference is a problem in the higher RPM ranges. For years the racers basically blocked about 1/3 to 1/2 the passage diameter between the pump and block passages which goes to show you how big the problem can get at continious racing speeds on long tracks.
The reverse rotation pump with the OEM style serpentine belt moves the excess flow issue to the drivers side where there is no bypass hole. But in a fit of wisdom! GM's new generation of engineers realized the original bypass was ineffective and the engines ran fine on the street so there was no need to duplicate the bypass on the drivers side and at worst there was a negative value in keeping it on the passenger side with the reverse rotation pump. So they simply pluged the hole. Simply cheaper than developing a new casting for the pump or changing tooling for the block.