KenNone whatsoever...I use these with a Stewart thermostat with the three 3/16 holes sending more water to the radiator which is a modern core (not Alum) with stock tanks ect..Topped off with a six bladed fan..Nearly impossible to get the temp over 175 degrees..even with stop lights in the Texas summer..However the engine is stock and well tuned so the cooling equation is not so difficult..
The impellers cost about $100 FYI