Outlet Shapes & Sizes
Believe it or not, the shape and form of the radiator outlets might have a profound effect upon cooling. Now, we don't have any concrete proof of this, but we've witnessed one particular car (a high-horsepower 427 big-block-powered example) that went through two different radiators, from two separate manufacturers. The only (visible) external differences were the shapes of the outlets.
One had formed outlets with soft bends, and the other had fabricated outlets with sharp bends (virtually a series of 45-degree joints). The car consistently boiled over with the sharp-bend equipped radiator. With no other changes (aside from the radiator swap), the operating temperature was entirely satisfactory with the formed outlet radiator. The theory was that the sharp outlet corners actually restricted the coolant flow, perhaps more than we knew.
There might be more here, too: Typically, a formed radiator hose (the type that Detroit uses on their vehicles) will deliver superior performance to one of those universal "fits-all" hoses that are available at the local discount auto parts store. The belief is there is considerable laminar flow in the hose, and the ribs of the universal radiator hose disturb this flow. So what's the answer? Watch out for cheap, universal hoses, and be careful when selecting a radiator-smooth outlet bend radius are likely much more efficient than sharp, angular turns.
One of the secrets of cooling a high-horsepower car is the use of a proper fan. Now, it's no secret that electric fans are pretty much the norm today. But there's a catch when it comes to fans: You have to get something with sufficient power to cool the car, but at the same time, get something that doesn't have a ridiculously high amperage draw. This is critical for many cars because of the drain on the charging system. Remember that slow speed equals low airflow through the radiator, and that can result in overheating if the fan(s) isn't up to snuff.
Companies such as Ron Davis Racing Products, Be Cool, Flex-a-lite, Alumitech, and Fluidyne, have spent considerable time researching cooling fans with these criteria. They offer a variety of fans in different sizes and they move air at different rates-some push the air, some pull, and there is a choice of material. For example, the Ron Davis specs are as follows:
Diameter RPM CFM 12-inch 2,300 1,576 14-inch 2,400 1,828 16-inch 2,400 2,197
All of the above have a low-amp draw, but Ron points out that one of the other secrets to properly cooling a high-performance car is to effectively seal the radiator to the fan. Typically, an integral shroud surrounding the electric fan accomplishes this. The shroud simply allows the largest volume of air to be moved through the radiator. There's more, too: If you take the time to effective seal any gaps between the fan shroud and the radiator, then cooling can improve. It's not that difficult to accomplish.
When all is said and done, the real key to cooling a potentially hot-tempered Chevy is to take care of the details. Buy good quality parts and make sure the fan, hoses, and shroud are appropriate for the application. If you don't pay attention to this stuff, you'll live to regret it, especially when hot weather rolls around.