The dog days are fast approaching. If you've added horsepower over the winter, there's added pressure-more horsepower equals more heat. And with that comes the need for cooling system attention. Of course, one trip to a local car show in the heat of the summer with an inadequate cooling system will make you wish you had paid more attention to the heat pump under the hood.
What the Radiator Really Does
It's no secret that a high-performance engine produces heat, and a bunch of it. Roughly half of the total heat energy produced by the engine is transferred back to the cooling system. In a conventional liquid-cooled application (i.e. your typical Chevy), the heat energy moves into the radiator and is then "radiated" back into the atmosphere. Taking this one step further, a liquid-cooling system operates very simply. As the coolant (to keep things simple, let's use plain water as an example) temperature approaches 212 degrees F, air pressure begins to build.
Since the radiator is closed (with a cap), pressure is allowed to build from within without any opportunity to "escape." This air pressure actually expands, which in turn allows the water to reach a temperature higher than 212 degrees F before boiling. As the air pressure increases, so does the boiling point of the water. Basically, this is an efficient system that works well in passenger car applications, but if the water temperature continues to increase (without leveling off), then the internal pressure will be too great for the radiator cap to handle. The result? A boil over.
There's more here, too. The radiator in such a system is a huge tank that allows large amounts of hot coolant to come in contact with an equally large amount of hopefully cool air. The coolant is first forced into the radiator side tank, or the upper tank if it's an old fashioned non-crossflow system. From this point, the coolant makes its way through rows of very small copper or aluminum tubes, finally returning to the adjoining side tank where it is returned to the engine. While the coolant has progressed through the tiny tubes, it was cooled by air flowing over and beside the tubes. The primary purpose of the "fins" contained within the core (and surrounding the little tubes) is to direct airflow into the proper area of the radiator. There are, however, secondary reasons for the fins, as you'll soon see. The most common core construction is the tube-fin or the ribbon-cellular design.
Fin count plays an important role in cooling. As a rule of thumb, a radiator will normally have between 8 and 14 fins per inch. When the fin count number is increased, the radiator can "radiate" more heat to both the surface airflow and the surrounding air. Unfortunately, as fin count increases, so does the opportunity for plugging, especially by bugs, dirt, and other foreign road junk.
Copper Or Aluminum?
When it comes to radiator construction material, what's better: copper or aluminum? Detroit has recently embraced aluminum as the radiator material of choice. There's a reason for this, aside from considerable vehicle mass reduction (aluminum radiators, on average can be as much as 1/3 lighter than an equivalent copper-brass radiator). And that's cooling capability.
Certainly the choice of copper is a good one for radiators. It has better heat dissipating properties than aluminum. But there's a caveat: The primary source of cooling in any radiator is the tubes. Heat dissipates from the coolant through the tube walls. This heat is then transferred to the fins that are in contact with the tubes. In turn, this provides a secondary source of cooling. As air passes through the fins, the heat is carried away.
Radiator manufacturers know that wider tubes are more efficient because there is more tube-to-fin contact (in a typical modern aluminum radiator, the tube-to-fin contact surface area is increased by 20 percent over an identically sized copper/brass unit). This isn't possible with a copper-brass design, because of tube-wall thickness limitations. Today's radiator technology (which typically uses wider tubes inside aluminum radiators coupled with multi-louvered fins) has allowed the aluminum radiator to cool efficiently. Just as important, aluminum units are now as strong, if not considerably stronger than their copper-brass counterparts.
Aluminum radiators simply cool better. Tests from various sources document a 28-percent increase in performance over a brass-copper equivalent, provided both radiators are identical in size. In truth, the use of aluminum in radiator construction can lower engine temperature by 30 degrees. Any vehicle will benefit from an aluminum radiator, including your high-performance Chevrolet.
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.