Cold Case radiator # mop 755k

the top picture is the same pulley.. its a factory 70-up small block with power steering and no a/c. the water pump groove is 6 9/16"

the lower picture is the water pump pulley that matches that crank pulley and measures 6 7/8.


so whats the ratio with a 6 9/16 crank pulley and a 6 7/8 water pump pulley?

That’s about 5% UNDER driven right there.