I always thought that more layers in a copper radiator were better for cooling. Summit racing said that in an aluminum radiator the 4 layer ones did not cool as well as a 2 layer. If I want to run my AC on my 1972 cutlass S 350 auto trans, would a 4 layer copper radiator be best or should I get a 2 or 3 layer aluminum radiator? Especially if I am towing a trailer.

 

A 2 core with 1" or larger cores is the way to go.

 

That is true for copper. The important metrics are surface area for heat transfer from the coolant to the air and flow restriction in the tubes. In addition, aluminum is stronger than copper and thus it's possible to make larger tubes our of aluminum. You can't directly compare four 5/8" copper tubes with two 1" aluminum tubes. The copper has more surface area but the aluminum has less restriction.