You would really have to ask radiator manufacturers why they rate it by horsepower. When Champion's site says one radiator is "good to 400 horsepower", another is "good to 600 horsepower" and a 4 core is "good to more than 700 horsepower".
But why did I ask about horsepower? Well, my line of thinking was that to make more power, you're going to either need more cubes, more compression or more cylinder pressure. More cubes create more area to cool, more compression creates more heat, as does more boost. Gotta be a way to get that heat out, right? Like through the radiator? Which brings me back to my original question(s). Now that that's all out of the way, did you have a 22" radiator made of alumninum in anything with lots of cubic inches or lots of compression that was street driven that you kept under or at 180°? If so, what brand was it and how did it fit and what modifications did you have to make?
Thanks.