The correct answer to your question should be based on the number of water circuits and the diameter of the water lines going through the mold. Just going by assumption based on a 270T machine with a 20 cavity mold a 1 HP pump should supply you plenty of water at a good pressure of 40 to 60 PSI. While a 2 or 3 Hp pump would also work anything above that is overkill and wouldn't provide any benefits at all.