How about cuz the compression ratios were in the basement, the carbs were miniscule, the cams were ancient low-rpm technology, the exhaust manifolds tiny, and if the trans was an auto, it often had just two gears, while the manuals were fresh out of farm-equipment, which was all ok, cuz the roads were so poor you couldn't get any speed up anyway..
It is generally written that whatever power comes out of the crank, double that went into heat; Half into the exhaust system and half into the cooling system. If you only have 100 or 150 crank horsepower, the cooling system doesn't need to be real fancy.
But when the engines get to be pumping out 450 at 5500, well now we have a heat problem
