Keeping heat from overwhelming...
Keeping heat from overwhelming your engine can spell the difference between a good day and a bad day at the track.
Few things in a racer's life are more frustrating than a fast car that you cannot keep on the track for an entire race because of niggling mechanical problems. One of the most common examples of this is chronic engine overheating. You know the scenario: You're running great but notice that the water temperature needle keeps creeping steadily upward. You stand the chance of a good finish, but you can't afford to throw away engines like last week's newspaper, so once the needle pegs 250, you reluctantly bring the car in and watch the race finish just like the rest of the crowd.
When it comes to your engine cooling system, proper choices can help prevent this problem. A quality aluminum racing radiator is a remarkably efficient device, but if it isn't installed and used optimally, it can let you down. Here are a few tips for making the most of your old water box.
The radiator that provides...
The radiator that provides the best cooling for your needs may surprise you. What works best for the Nextel Cup guys isn't what's best for the Late Model racer on a half-mile track. That's why radiators such as C&R's Late Model radiator aren't just a stripped-down, cheaper version of what the Nextel Cup teams get; it is designed to meet different demands.
The greatest difference between a quality racing radiator and an off-the-shelf piece is how it was put together. A radiator works by providing the most efficient conduit possible, which is done by using the thinnest aluminum possible. This, however, makes it difficult to create a watertight seal. In the good ol' days, manufacturers had to use epoxy to seal the tubes to the tanks on either side of the radiator. Today, the best radiators are mainly sealed with TIG welds, and a process called brazing reinforces the seals. This provides not only a leak-proof radiator, but also one that produces the most efficient heat transfer possible.
"New technology radiator cores are made so that the tube-to-header bond is 100 percent, so epoxy isn't necessary," says Chas Howe of Howe Racing Enterprises. "This is done in most racing radiators with furnace brazing, which is where the aluminum radiator is heated to a near-molten state under a vacuum so that the fins, tubes, and header all bond and become one piece. This is a better way of doing things because the better contact you have between surfaces-especially between the tubes and the fins-the more heat is going to transfer from the water and into the air via the radiator."
A radiator with an integral...
A radiator with an integral heat exchanger will have a wide manifold on one side. This is an example of a Fluidyne unit with a separate oil cooler (top). With this design, the cooler is moveable and can be placed above or below the radiator, or anywhere else on the car as the racer sees fit.
The biggest decision to make when determining which radiator fits your needs is the thickness and fin count. For Saturday night racing, most manufacturers seem to prefer a two-row radiator with fins spaced to approximately 15 per inch. In applications where the height or width of a radiator is limited by framerails, manufacturers can run three or even four rows of tubes, one behind another. This allows more cooling for a smaller radiator, but the added thickness stalls the air as it moves through the radiator core. Keith Robertson of Fluidyne says his company only recommends a three-row radiator for high-speed tracks, generally a mile or greater in length. Otherwise, the incoming airflow just isn't strong enough to push its way through the radiator core effectively and provide efficient cooling. At high-speed tracks, the thicker radiators provide adequate cooling in a smaller area, allowing the team to tape off more of the grille.
An interesting side benefit of three- and four-row radiators, however, comes from the fact that it is difficult for air to move through them effectively. Air tends to "pile up" in front of the radiator core. The result is that less air makes it through the radiator into the engine compartment and is instead forced to flow up and over the car-providing more downforce.
Fin count works on much the same principle. More fins per inch allow more radiant cooling, but they also block air from moving through the core. If you are racing big, high-speed tracks, you likely will want to increase your fin density. If you race half-mile short tracks, your best bet is to stick to a density of 14-18 fins per inch. This will allow plenty of airflow through the radiator core and provide the best cooling for your needs.
This radiator includes the...
This radiator includes the heat exchanger. Notice the extra volume and connections on the left side.
Oil Coolers versus Heat Exchangers
If you are racing a high-output, dry-sump race engine, you probably need some form of additional oil cooling. If you need all the engine cooling you can get, a separate oil cooler is probably the best bet. This requires extra lines, extra space, and extra money. The second option is an integrated heat exchanger in the radiator. It functions by routing the oil lines through the radiator manifold. The heat from the engine oil is passed to the water and eventually to the air as the water flows through the radiator tubes.
"I think in most situations you would prefer the heat exchanger because it's more compact, there are fewer lines, and it's less prone to damage," Howe says. "I would recommend that to anyone running a good, professionally built dry-sump engine. If you are running an engine that is borderline on temperature already, the bad thing about cooling the oil through the water is, of course, it warms the water up. So it does take away some of the capacity of the radiator to cool the water if you are also trying to use it to cool the oil."
A third option is a product Howe Racing Enterprises produces called Cool Tube. It's a finned, solid tube that replaces braided oil line and helps cool the oil that passes through it. Cool Tube isn't designed to be a sole source of cooling, but it can be an effective supplement to your oil cooler or heat exchanger. Simply find a straight section along the route of your oil lines to the oil tank that gets a steady flow of cool air.
The number of cooling fins...
The number of cooling fins per inch is an important design decision. While more fins mean more radiant cooling, they also reduce the amount of cool air flow through the core. For two-row radiators designed for Saturday night use, approximately 15 fins per inch seems to be the standard.
Electric radiator fans are one of the few areas in racing in which the benefit of saving a few horsepower doesn't come at the cost of something else. A mechanical fan driven off the crank can burn as much as 20 hp at 6,500 rpm, which is definitely a significant amount. In short feature races, you can often get by with running an electric radiator fan completely off the battery, causing absolutely no horsepower drain on the engine. You often have the option of simply turning it off at race speeds when the incoming air flow is enough to provide adequate cooling on its own. In longer races, or in situations where you're running a few electrical devices such as blowers, you will need to use a belt-driven alternator to keep a charge in the battery, but the horsepower that a good racing alternator requires is still much less than a mechanical fan.
The downside, however, is that electric fans do not pull as much as a properly shrouded mechanical fan. If you are racing tight, short tracks with high-horsepower engines-especially in the southern United States-you may have no choice but to run a mechanical fan.
An old myth in racing was that the water pump needed a restrictor to slow the path of the water through the engine. The thinking was that if water traveled more slowly through the engine, it would be able to pull away more heat. That thinking is completely wrong on several levels.
"In a racing application, I haven't seen a case where you can move too much water," Howe says. "The big enemy of the cooling system is cavitation, which comes when the water pump has to work too hard. Anything you do to restrict water flow can lead to cavitation, which hurts the system's ability to cool because it generates air. Even in a closed system, a cavitating water pump has the ability to pull air from the water.
"The argument I always hear is, 'We slow down the water so it spends more time in the radiator.' But the cooling system is a closed system. If it is spending more time in the radiator, it's also spending more time in the engine, so it's a wash. There is really nothing being advanced by using a water restrictor. You are resisting against the water pump, and I've never seen any advantage to that."
These are the cooling tubes...
These are the cooling tubes that hold the water that flows through the radiator. Different designs stack more or less tubes in the core depending on the cooling demands. Cooling tubes can also be different thicknesses.
Robertson at Fluidyne agrees and says it can even reduce a radiator's ability to cool the water. Slow-moving water, he says, allows laminar flow through the radiator tubes. Laminar flow means the water travels in a nice, straight line. The coolant flowing against the sides of the tubes stays there and gets nice and cool, which is good. But the coolant travelling in the center of the tube also stays there. Because it has no contact with the aluminum tubing, it does not have the same opportunity to radiate off as much heat and does not receive adequate cooling.
Engine coolant that rushes quickly through the radiator tubes, however, becomes turbulent. Instead of flowing smoothly, it moves more haphazardly through the tube, which promotes more homogenous cooling.
Care and Feeding
Once you have laid out your cooling system, it's important to take care of it properly to make sure it doesn't lose cooling capacity over time. Chet Blanton of C&R Racing points out that making sure you have absolutely no air in your cooling system is one of the most important things you can do to ensure its continued effectiveness. Air in the engine block-or especially the cylinder heads-causes hot pockets that the coolant cannot reach and promotes all kinds of bad karma. Also, if air pockets are pushed through the radiator's narrow cooling tubes, it can cause the tubes to swell and crack. Even if they don't crack, Blanton says the expansion can cause the cooling fins to be smashed together. Now you have a mystery on your hands. You have a radiator that used to work properly and it isn't leaking, but now for some reason it isn't adequately cooling the engine. It's a problem that can be difficult to diagnose.
One of the best ways to make sure air stays out of the cooling system is to run a surge tank. Instead of filling the cooling system through a neck in the top of the radiator, it is filled through a surge tank that connects to the radiator. The tank is mounted so that it is the highest point in the entire cooling system, including the radiator, all hoses, and cylinder heads. Water or coolant stays in the surge tank and is drawn into the system as necessary, and any air in the system will find its way to the surge tank because it is constantly trying to find the highest point in the circuit.
Also, as you race-either on asphalt or dirt-the fins in the radiator will eventually become clogged with dirt, rubber, or other racing debris. Resist the temptation to blow all this junk out with the pressure washer when you're washing off the race car. A high-pressure stream of water can bend or otherwise damage the cooling fins. Robertson recommends only gently-flowing water to flush out the loose particles and periodically soaking the entire radiator in soapy water to remove anymore determined pieces of trash. He also strongly discourages the use of solvents. It may work the first time to get rid of pieces of tire rubber, but the residue of that solvent will remain and attack the next piece of rubber that becomes lodged in the cooling fins. This time, however, that will only be enough to cause the rubber to soften and swell, which will only make it that much harder to remove the next time around.
Cooling Better with Water Wetter
If your existing cooling system is struggling to keep your race engine at a manageable temperature, you may want to consider helping it out with Red Line Oil's Water Wetter product. Water Wetter is a coolant additive that is supposed to improve water's ability to absorb heat from the engine.
Pictured is a breakaway of...
Pictured is a breakaway of a cooling fin from a Fluidyne radiator core. As you can see, cooling fins aren't smooth. They are actually louvered to increase surface area and cooling. If you try to clean your radiator with a high-pressure stream of water, even though the fins look OK on the outside, the water can close these louvers and reduce the radiator's efficiency.
"It improves heat transfer and reduces cylinder head and overall coolant temperature," says Dave Granquist of Red Line Oil. "Water Wetter does this by reducing the surface tension of the water, and it promotes nucleate boiling. This means that it promotes a more efficient heat transfer off of the hot spots in the engine. The upper cylinder walls and the cylinder heads are bad to trap water in crevices, and the lower surface tension helps reduce that.
"We have seen reductions in temperatures of 20 to 30 degrees," he continues. "This is mostly in situations where we can optimize the cooling system. Typically this is where we can get rid of the antifreeze and just use water and Water Wetter, which is the best combination for heat absorption."
Let The Buyer Beware
When researching this article, Chet Blanton of C&R Racing offered us a tip that we hadn't thought of before: At least when it comes to radiators, the high-end expensive stuff may not be the best for your needs.
"The worst thing we run into here," says Blanton, "is if some guy goes and buys a radiator off of eBay or some discount warehouse place that sells used parts. Then he calls us and says, 'Hey, I've got this radiator that's one of yours, and it's not cooling.' I'll ask a couple of questions and find out he's running at a half-mile track and the radiator he bought is 4 or 5 inches thick.
"He'll brag that it's a radiator that was run in one of Jack Roush's cars or some team like that, and it should be the best thing available. Well, it is for a Nextel Cup guy running a high-speed track, but for this guy running a half-mile track in a car that's considerably slower than a Nextel Cup car, that's not a good radiator for his needs. The low-budget guy may think he's saving some money by buying used parts, but if you try to buy a Daytona radiator for running at your half-mile track, that's going to be totally wrong."