We are looking at Part 2 of the radiators for a high-performance Corvette engine. This article appeared in our December 2018 issue of Vette Vues Magazine titled “High-Performance Radiators Are Not Created Equal” by Wayne Scraba. You can read Part 1 Here.
Photos courtesy and copyrighted to DeWitts Radiator
BOILING POINT – PART 2
Remember, in the last issue (Vette Vues Magazine, November 2018), when we talked about misleading information with regard to radiator construction? There’s more: Some companies offer radiators configured as a double-pass or triple-pass configurations, and while that sounds extraordinary, the reality is it’s a wee-bit misleading: It sounds as if a double-pass radiator forces the fluid goes through the radiator two times. Unfortunately, that is not true.
Double-Pass or Triple-Pass Radiator Configurations?
According to DeWitts, a double-pass design consists of nothing more than a baffle welded inside the end tank. What this does is cut the radiator in half, and the fluid flows through each half in series. Because each section is half the size of a full core, the fluid velocity is twice as fast, and the pressure drop has now doubled. Some will argue this design is superior because the fluid stays in the radiator longer. The reality is that the fluid has twice as far to go, but it is also traveling twice as fast. In the end, the fluid flows through each tube only one time, and a more appropriate description would be a “U-flow” layout. The design also demands both inlet and outlet to be on the same tank (which in some Corvette applications can prove rather troublesome).
What about a triple-pass radiator? This layout has two baffles, one in each end tank. Now the core is divided into three small sections and flows through each one in series. This creates very high flow rates, and high-pressure drops through the system.
On that note, what about three-row aluminum radiators – are they better than two? In the old days of copper and brass radiators, this was true. More rows meant more surface area in contact with the fin and, consequently, a higher heat rejection. Because of this, a 3-row radiator was better than a two-row rad and so on. When aluminum radiators came onto the scene, the rules changed. By lowering the fin height, you could stack more layers of tubes. Using wider tubes increases the tube-to-fin contact area. The result of this is a very high-performance radiator with huge savings in weight.
What is the Four Core Radiators?
Fair enough, but what about “four core radiators”? There is really no such thing. The term “four core” has been misused for decades and accepted for generations (the writer is guilty too!). The term “core” is used to describe an assembly of parts. This assembly consists of tubes, fin, headers, and side plates. All these parts are brazed together to create the core. A radiator core can be made in several different configurations and materials. It could be made with copper or aluminum, and each layer consists of a group of tubes and fin. The number of tubes in each layer can vary based on the material and application. In this case, the term “four” is referring to the number of tubes in each layer. The correct term is actually “four-row,” referring to the number of tubes.
Aluminum Radiators are now the norm…
Since aluminum rads are now the norm, there’s even more confusion. That’s because the whole design concept of the radiator changed. The tubes in aluminum radiators tend to be much wider than the older copper units. This provides more contact surface and less dead space between the tubes. The height of the fin in aluminum radiators is also much shorter, and that will result in more layers in the same given space. Because of this, an aluminum radiator with two rows will exceed the heat rejection of a copper radiator with four rows.
When considering tubes in an aluminum rad, note that the U.S. standard for performance aluminum radiator tubes is a 1.0-inch wide tube while imported “offshore” radiators have smaller 16mm (0.62-inch) tubes. In this case, a 3-Row aluminum radiator would only have a total of 1.86-inch of the tube-to-fin contact surface, which is less than the two-row core with 1.0-inch tubes. Some ads for these 3-Row aluminum radiators will reference several features of the radiator design, but they avoid discussing the issue of the tube width. In contrast, is the DeWitts radiator: They offer a radiator design that goes another step and offers a two-row core with 1.25-inch tubes or (2.5-inch) tube-to-fin contact, and this configuration would again exceed the performance of a “4-row” imported core design. Always ask about the tube width. That will tell you a lot about the heat rejection and the origin of the product.
Is the company the Manufacturer or just an Assembler?
Something else to consider is if a rad company is actually a manufacturer or just an assembler. According to DeWitts,” “When it comes to really building radiators in-house, not that many companies actually own an aluminum brazing furnace. Many companies claim to make aluminum radiators when, in reality, they just purchase the components and assemble radiators. Some companies may not make anything at all and just re-sell a brand made elsewhere. DeWitts owns their own aluminum-brazing furnace, and they point out that aluminum brazing requires a very high volume of nitrogen gas. The bottom here is, if a radiator company does not have an industrial-grade nitrogen yard (Editor’s Note: DeWitts operates a massive 3,000-gallon system), they do not make their own cores.“
There are some other technical considerations to ponder (and some we’ve mentioned before, but they’re worth repeating): 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. Still, we’ve witnessed one particular car (a high horsepower 427 big block-powered example) that went through multiple radiators in an effort to resolve a cooling issue. The only (visible) external differences between the radiators were the shapes of the outlets. The rad that worked was built with formed outlets with soft bends. The others had fabricated outlets with sharp bends (virtually a series of 45-degree joints). The car consistently boiled over with the sharp-bend equipped rad. With no other changes (aside from the rad 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) and most likely had a serious effect upon laminar flow.
There might be more here too: Typically, a formed radiator hose (the type Chevy always uses on their Corvettes) will deliver superior performance to one of those universal “fits-all” ribbed hoses that are available at the local discount auto parts stores. 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? Simple. Watch out for cheap, universal hoses, and be careful when selecting a rad – smooth outlet bend radius is likely much more efficient than sharp, angular turns.
We’re not quite done yet: Another question that regularly pops up with dealing with radiators is capacity. We asked DeWitts about the volume of coolant their typical radiators hold: “Most cars produced prior to 1983 used three or four-row copper radiator cores with large brass tanks. In this case, our radiators hold the same volume as the factory unit. Cars produced after 1983 were equipped with a single row aluminum radiator with plastic end tanks. For these applications, our double row aluminum radiators will hold (1) one additional gallon over the factory unit.”
Need a Stock Looking Radiator?
What if you want a radiator that looks close to stock? That’s where the folks from DeWitts can help you out. Virtually all of their replacement radiators are built with OEM-appearing tanks (although they are obviously built from aluminum). Case-in-point is one of the radiators shown in the accompanying photos. It not only looks like a stock style rad for a first-generation big block Camaro (or 1968-70 big block Nova), it also has dimensions similar to a stock rad, and it accepts a stock or exact reproduction fan shroud. The radiator even has built-in clips to hold the shroud in place. DeWitts offers similar setups for all sorts of Corvettes too. Obviously, DeWitts can supply radiators such as this with an electric fan setup too. Radiators for select early Corvette examples make use of a single 16-inch electric while most of the crossflow examples for later model cars incorporate dual fans (usually 11-inch or 12-inch examples). The fans are all top of the line Spal components (they even offer brushless motor fans as an option). Most of the fan and shroud kits can be retrofit to existing DeWitts radiators too.
For the LS swap crowd, DeWitts has a wide range of available rads for Corvettes too. You’ll find that each application (LS Swap or conventional) bolts-in place using the system your particular Vette was designed with. Many applications use a lower saddle mount to support the radiator and to isolate it from vibration. Others make use of side mounts. Here, the radiator is bolted to the radiator support by way of two to four rubber cushion well-nut mounts.
Something you might want to consider for a stock appearing Corvette rad is DeWitt’s “Black Ice” coating. It is a semi-gloss black coating that gives your aluminum rad the look of a vintage copper-brass example. This is a two-part epoxy paint engineered to adhere to aluminum radiators. You can have it applied to a new rad, or you can apply it yourself. It is applied by way of an air type spray gun, and only one or two coats are necessary. It cures in approximately 12 hours, and as the solvents evaporate, the product shrinks to provide a very thing 0.002-inch film. DeWitts notes that this think skin will protect the aluminum with having any adverse effects upon heat transfer (keep that in mind when painting any radiator).
The pressure cap is important, but some folks get it wrong when it comes to rad caps. Here’s why: Recall in the first segment when we talked about pressurizing the cooling system? Pressurizing the cooling system raises the boiling point of the coolant 3 degrees for every one pound of pressure. DeWitts notes this does not have anything to do with how your cooling system will perform. It only sets the point at which your coolant will boil. A coolant mixture of 50/50 (water/antifreeze-coolant) has a boiling point of 238 degrees. Pressurizing the system 15 psi will change that point to 283 degrees, but it will not change the coolant running temperature. Pressure caps are available with ratings of 7-20 psi, and any cap in that range would work. As a result, DeWitts recommends you use a cap in the 13-15 psi range. More on DeWitts pressure caps in the accompanying photos.
What about coolant? What coolant is recommended for an aluminum radiator? According to DeWitts: “Actually the quality of the water you use is more important than the brand of coolant. Aluminum is very sensitive to minerals and chemicals in all sources of water, and only distilled water should be used. We recommend that you purchase a “pre-mixed” extended life coolant of your choice. This eliminates any chance of using the wrong source of water and simplifies the process of mixing, filling, and adding coolant.”
As you can easily see, there is a whole bunch more to modern aluminum radiators than first meets the eye. If the rad is expertly manufactured, then it will actually prove to be filled with (extremely) high tech features. For a closer look, check out the accompanying photos. With proper selection, these rads will keep your Corvette cool during the dog days of summer.
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