[mechanickeith]

Ok,,,Here is the real deal about NAPA 4 bolt Pontiac water pumps. The 4 bolt pump with a cast impeller that works with all Pontiac V8's till mid year 63 is part number 58-594 at NAPA. Cast pump & impeller, cost at my napa is $111.39 plus tax. For comparison, the EXACT same pump but with a stamped impeller is $43.98,,, Thats a 67 dollar difference for a cast impeller!!!! As I cant get the correct impeller 4 bolt pumps for my Tempest 4 cyl cars, I buy the stamped impeller pump, press it apart & put the cast impeller on the new pump. You may be able to take this NAPA number & cross reference to a different parts house & come up with a different price/pump. BUT need to ensure it has a cast impeller that is correct for the V8 motors. There were several different cast impellers made but I see no reason that they wont work fine on our V8 Pontiacs. Look at the attached pictures. In the 4 pumps in a row,,,the pump on the far right is for a V8. Look at the gap between the impeller & the housing. The Tempest pump (# 1 & 3 ) has about a 1/2 inch gap between the housing & impeller & has very short vanes on the impeller. This is so it sits in the rear half of the timimg cover & only pumps water to the right side of the motor.The V8 impeller is close to the housing & has deep vanes. This pump impeller fills the entire timing housing & pumps water to both banks of the motor. Last picture is of a different style of cast impeller for a V8 pump. You can use the V8 pump on the Tempest motor with no issues. If you use a Tempest pump on a V8,,,the left cylinder bank will overheat due to a lack of moving coolant. Hope this helps!!!