Using a high capacity water pump helps to reduce cavitation in the water jackets at higher RPM.
This higher capacity water pump with larger impeller moves more coolant than the small impeller GWP132 (803/850/997 Blocks) This pump has a bypass. The impeller protrudes into the block slightly more than 1/2″ and fits all 1275 Blocks and most 998/1098 blocks from 1967.
The impeller in these aluminum bodied pumps is long lasting cast iron, not stamped steel as in many aftermarket pumps. This water pump will fit all 1275cc blocks and all small bore blocks, with the exception of early 803/850/997cc units. These will need an amount of modification, relieving corrosion and slight material from the liner wall and impeller if required should enable clearance, try spinning pump loosely fitted without gasket for clearance
Further reduction of cavitation is achieved by using a large diameter water pump pulley, If using a larger pulley it is necessary to check clearance between the large pulley and the head.