Engine builders are jeopardizing horsepower and increased durability if they don’t consider the radiator and cooling system as a critical part of the performance equation.
“For a lot of engine builders, the cooling often gets overlooked,” says Chris Paulsen, founder of C&R Racing and first-day speaker at the Advanced Engineering Technology Conference in Indianapolis. “Obviously, by optimizing cooling, you optimize horsepower.”
Paulsen’s presentation focused solely on aluminum-core radiator technology, even as copper proponents continue to emphasize that metal’s superior heat transfer properties.
“If we could ever figure out how to build copper tube and fittings that could hold the pressure we want, we’d have something special,” counters Paulsen.
Serious technology has been invested in radiator core design, especially for exotic designs found in Formula 1 cars that can cost upwards of $6,000 per core. While a few NASCAR teams have tried similar products, car owners cringe with every bump draft or head-on encounter with a tire barrier.
“A lot of the technology is in the tube itself,” explains Paulsen, noting that older radiators were basically rows of half-inch tubes. “Now we’re making the tubes much wider. The more surface contact, the more heat rejection.”
Developments in extrusion allow thicker metal on the leading edge of the tube to ward off debris, compared to rolled and welded tubes that start off as flat sheets of aluminum.
“They are not nearly as a strong as extruded and won’t handle the pressure, and pressure is the key in today’s world,” says Paulsen, adding that even more technology goes into the design and manufacturing of tiny louvers on the fins between the tubes.
With regards to water flow, Paulsen admits there is a lingering theory that slow flow allows the water a chance to absorb the heat.
“We like a high flow rate,” stresses Paulsen. “It helps keep the hot spots down and higher flow rates create turbulation, which is where a tremendous amount of heat rejection comes from.”
Paulsen says higher flow rates are especially critical in applications where the radiator can get clogged with debris. Of course, higher flow rates are dependent on improved water pump designs, and manufacturers have relied on CFD analysis to respond with new impellers, housings and tighter tolerances.
“The negative side to the water pump is that they’re still a high parasitic loss,” adds Paulsen. “We’re seeing anywhere from eight to 12 horsepower loss.”
Computer modeling has also helped improve fan design over the traditional Ford 4-blade mechanical unit that was quite popular in NASCAR for years. And the move to electric fans has embraced brushless technology for even more control as well as performance.
“We’re doubling airflow over a typical brush motor fan,” says Paulsen, “The only problem is heat, and currently in some applications like NASCAR, the air discharge temperatures are so high that a brushless won’t work.”
Air discharge temperature have risen in NASCAR because the engine oil cooler has been mated behind the radiator. Previous setups had a separate oil-to-water heat exchanger.
“About six to eight years ago, we started doing what we call a full-surface oil cooling behind the radiator,” says Paulsen. “What we found is it really helps air distribution through the core face of the radiator. However, we’re seeing in some cases up to 330 degrees of air temperature coming of the back of the that heat exchanger.”
Since cooling is so closely related to vehicle aerodynamics, duct work to the radiator becomes even more critical to vehicle design.
“Obviously, take the air and use it the best you can,” says Paulsen. “Open-wheel cars with side pods have the ability to design the perfect radiator duct to really draw air and increase velocity.”
Paulsen talked extensively about spec’ing out a radiator. A number of factors come into play, including type of track, vehicle speed, on- and off-throttle times and potential for debris in addition to typical engine data.
Another factor that often concerns racers is weight.
“But many times people will trip over performance for weight,” says Paulsen.
Some marketing campaigns have led some racers to consider coolants other than plain distilled water.
“Nothing works better than pure water, or at least nothing we can legally use,” says Paulsen. “Antifreeze will definitely not lower temperatures but it does have anti-corrosive properties.”
Regarding corrosion, everyone knows that aluminum will corrode. However, there is the dynamic called passivation. Paulsen says C&R radiators are completely clean after coming out of the brazing oven, then filled with water and pressure tested followed by a second oven dry before shipment. Some race teams, however will pressure test their new radiators using tap water but then put them back on the rack without drying.
“After while they put in a car and it becomes a garden sprinkler,” says Paulsen. “The passivation process hadn’t happened in that radiator. It’s a situation that as the aluminum heats up and cools with water flowing, it actually treats the material and makes it a lot tougher. So keep that in mind with brand new radiators, don’t get them wet and then let them set.”
Paulsen’s final topic was pressurized cooling systems.
“It’s an aerodynamic device. It doesn’t create power. It doesn’t run cooler,” says Paulsen. “It simply allows you to run a lot hotter safely. But the systems have to be designed to support that pressure.”
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