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Dirt Track Cooling Tips

So your Late Model, Bomber or Sportsman racer is overheating when rim-riding the berm of clay. You have performed the cooling system maintenance, right?  Because if we assume (you know that makes an ASS of U & ME!) your cooling system is operating properly, you’ll just end of throwing parts and money at the problem.  We sat down with AFCO racing experts Brandon Kight & Eric Saffell, and some local dirt track hotshots to get some tips on what to look for when your racer blows its stack. Everyone told us, maintaining the cooling system should be chore number one.

“Often times one component is blamed for a cooling problem” explained AFCO’s Kight.  “Keep in mind that there are a multitude of components to a cooling system.  Air flow, water velocity, ambient air temperatures, etc., and they play key roles in overall cooling system performance.  If you’re having cooling system problems, each component must be considered. As an example, a car with a cooling problem using a 15” fan blade with limited ram air available may require a higher cfm fan to adequately pull enough air through the radiator.  Switching from a 15” to a 17” fan can aid in cooling with a 40% increase in air flow”.

“The goal of the cooling system is to remove heat from the engine that is generated by the production of horsepower and friction”  said Saffell.  “It does this by circulating hot coolant through the engine pumped by a mechanical or electrical water pump to an air to liquid heat exchanger that we call a radiator.  This hot water passes into the radiator and transfers the heat energy to the tube.  The heat is transferred from the tube to the fin and from the fin to the air that is passing through the radiator”.

Cooling System Maintenance Tips:

Radiator: Do the obvious: Check for leaks or clogs. See below for Head Gasket problems. Take it to a professional radiator shop for cleaning and a pressure check. Are the fins closed off? If so, take a small screw driver and gently pry them back open.  Are the fins clogged with clay, dirt and rocks? High pressure water sprayed from the backside (engine side) after a night of racing can help.

AFCO Technician performing a radiator leak test.

Radiator Cap: Is the cap holding pressure?  Higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the cylinder heads more efficiently. Stewart Components’ web site recommends using a radiator cap with the highest pressure rating that the radiator is designed to accept. In general, performance radiators will accept 22-24 PSI, and professional racing radiators will accept a 29-31 PSI.

The coolant will typically only build to 16-18 PSI, due to expansion up to 200°F. However, if the engine does overheat, the pressure inside the cooling system could reach as high as 28 PSI. Once the radiator cap has opened and vented coolant, the engine will not cool down until it has been turned off. The radiator cap is basically a “safety valve”, so always use the highest pressure radiator cap that your radiator will tolerate. Kight also recommends a new cap, “Radiator cap gaskets will take a set over time and may not match up exactly with the new filler neck on the replacement radiator.  This is more prominent when replacing one brand of radiator with a different brand of radiator”.

TIG welded radiator neck

Thermostat vs. Restrictor: Are you running a thermostat? For applications requiring a thermostat to keep the engine at operating temperature, make sure it is a high flow racing thermostat, like Mr. Gasket, Stewarts/RobertShaw, or Milodon. These high performance thermostats are designed to resist large variations in coolant pressures that occur at high RPM’s where coolant temperature and coolant pressure fight for control of the thermostat keeping it from opening at its designated temperature. Is it opening? Put it in a pot of boiling water to find out. Is it of the correct temperature setting?  It should be stamped into the thermostat. If the setting is too high (opening at too high a temperature), like 195F, get a cooler thermostat, like 165F.

A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficient velocity. This situation is a common cause of so-called “hot spots”, which can lead to failures.

Years ago, cars used low pressure radiator caps with upright-style radiators. At high RPM, the water pump pressure would overcome the radiator cap’s rating and force coolant out, resulting in an overheated engine. Many mistakenly believed that this was caused because the coolant was flowing through the radiator so quickly, it did not have time to cool. Using restrictors or slowing water pump speed prevented the coolant from being forced out, and allowed the engine to run cooler. However, cars built in the past thirty years have used cross flow radiators that position the radiator cap on the low pressure (suction) side of the system. This type of system does not subject the radiator cap to pressure from the water pump, so it benefits from maximizing coolant flow, not restricting it.

Hoses: Again, check for leaks. Check the lower hose for softness; it can get sucked closed on intake / suction side of the water pump. Stewart recommends, “Standard full-size hoses should be used to ensure maximum flow. Smaller “AN style” hoses decrease flow and hence inhibit proper cooling”. Also don’t let the hoses get petrified before replacing them.

Water Pump / Belts: Are you using stock or race pump? There are significant differences between a stock water pump, and Stewart Components pumps. Most OEM pumps are built to meet standard performance requirements at relatively low RPM. Stewart says their pumps are designed and manufactured specifically for high performance applications. Are the belts slipping? Check for glazing on the belts and telltale chirp noises especially at startup. Same with hoses, don’t let the belts get fossilized, replace them.

Head Gaskets: The guys at AFCO showed us a radiator cross-section that was raced with a blown head gasket. The cylinder pressure leaked into the coolant system and ballooned the tubes.  Routine compression testing will give you clue when you’ve got a bad head gasket.

The blown head gasket radiator cross-section on the left.

Tuning: While we’ll not get into all of the possible tuning variables here, be aware that your tune can have a great effect on how hot or cool the engine runs. Here’s a quick rundown: Running too lean or too much timing will cause you to run hotter. What do the plugs look like? Are the plugs of the correct heat range? What fuel is being used?  Cooling is not an issue with alcohol fuel, as it burns very cool.

Ducting: Our sources did not recommend ducting of the grill to the radiator, like you might see on an asphalt car. Dirt tracking tends to pick up too much debris and clogs the radiator.

Improvements:

If your race car is still overheating after performing all of the needed cooling maintenance on your racer, you’ll need to make improvements to keep your cool by upgrading your weak links.

Fans / Shrouds: Electric fans have improved tremendously in recent years, in both quality and reliability. Electric fans now outperform mechanical fans in nearly every application, except towing and dirt oval track racing.

When using a mechanical fan, a properly designed shroud must be used. Most OEM mechanical fans are not designed for high RPM use: they can have serious vibrations problems when run over 6,500 RPM. This is a turbulence problem, not a balance problem, and will destroy the water pump and components in front of it. The large fans preferred by dirt oval track racers can consume up to 18 horsepower at 6,500 RPM. Do NOT run a mechanical fan that is any larger than required for the application. Mount fan 1/2″ away from radiator so the fan will pull air through the radiator not around it. Flex fans are a poor design for performance applications. They move less air at higher RPM, and only consume a fraction less power than standard fixed pitch fans. Clutch-style fans are inconsistent and are not recommended for any racing application.

Pulleys: Using the proper pulley and drive system is critical to matching the water pump’s performance to your specific application. Race applications require a maximum water pump speed of 7000 RPM. Stewart Components does NOT recommend the use of underdrive pulleys on any Street application. Stewart claims their high-flow water pumps only consume 2.26 horsepower at 4,000 RPM. According to Stewart, “In years of testing, we have consistently proven that the engine will lose more horsepower due to higher operating temperatures than any possible gain from underdrive pulleys”. Our racers suggested that up to 30% reduction pulleys were OK, but if not cooling properly, go back to a 1:1 pulley setup.

External Plumbing: Street-driven vehicles seldom need auxiliary plumbing or coolant lines. Small-block Chevy race engines with aluminum cylinder heads usually require extensive external plumbing to address two design problems:

1. Aluminum heads have smaller water jackets than cast-iron heads because the external dimensions are similar, but the ports are larger, the deck is thicker, and the material near the rocker stands is thicker, all leaving less area in the water jackets.

2. The siamese center exhaust ports are a design compromise that presents additional problems when aluminum heads are used. The area near the center exhaust valves is thicker, thus providing less surface area for cooling.

Stewart recommends installing a pair of –10 AN lines that connect the rear of the aluminum cylinder heads to the thermostat housing crossover in the front. This step will help offset the smaller water jackets. A pair of -10AN lines connecting the pressure side of the water pump with the area in the center of the cylinder head (just below the exhaust ports) will offset the lack of cooling surface area.

Double Pass Radiators: “Most race cars will attempt to run the nose closed and pull air from underneath of the nose panel to supply air to the radiator.  This is one of the reasons we have seen most professional racers go to a double pass radiator.  A double pass radiator allows for a more efficient cooling system utilizing the same given core area and air flow by first passing the coolant over the top half of the radiator then the bottom half allowing the radiator to dissipating heat twice from the coolant.”  says Kight.

“All of our double pass radiators are manufactured utilizing our exclusive 360 degree tig welded baffle that splits the radiator core into two sections.  This 360 degree design effectively splits the radiator into two sections and eliminates the possibility of any bypass occurring from the top tank to the bottom tank.  This design is superior to a partially welded baffle that permits bypass to occur.  A double pass does require more pump pressure to flow the same volume of fluid”, Kight added. Staffell continued the thought by saying “More cooling over standard type radiators, with less than 2 oz. of added weight. A double pass keeps your mind off the water temperature and puts it onto the race track. The 360 degree baffle in a sense creates two radiators out of one and assures that you won’t have any coolant that has entered the radiator but never made it across the core. This is superior to utilizing silicone to seal internal baffles, or worse, a partial weld that allows the coolant to bypass the radiator core completely”.

Flow with Welded Baffle

The core of AFCO Radiators:

Tube (a.k.a. Flute or Row): The tube in a radiator is the passage in which water flows.  It can vary by thickness, width (1”, 1.25”, 1.5”, etc.), shape (flat or oval), and quantity (single row, two rows, etc).  Staffell told us, “As a rule of thumb: a two row 1” per row AFCO aluminum core is more efficient then a 4-row copper/brass radiator while weighing in at half as much.  Wide tube construction spreads the coolant over a large surface area and allows for more coolant contact with the tube surface vs. a copper/brass radiator.  This wide tube construction allows for more fin contact area, which means more heat transfer can occur”.

Two Row AFCO core

Fin Design: The type of fin may vary from louvered, non-louvered, or foiled.  “All AFCO racing radiators utilize a louvered fin design.  A louvered /serrated fin will have the potential to remove more heat from the system then a non-louvered fin”, Eric told us.

AFCO louvered fin design

Furnace Brazed: The furnace brazing process applies heat to all the elements of the radiator core and brazes them together. Brandon explained, “Because of the effectiveness of the furnace brazing process, AFCO cores are free of epoxy on the header to tube joint. During the life cycle of the radiator, epoxy can dislodge, exposing a tube to header joint that needs the epoxy to seal the radiator. Once the epoxy becomes loose, the chance for failure is greatly increased”.

AFCO Furnace Brazed core

100% TIG Welded: “All AFCO radiators are 100% hand TIG welded by true craftsman at the top of their craft”, Staffell bragged. He continued by saying, “This gives the radiator the strongest and most uniform welds and the best appearing radiator available”.

Watch as AFCO’s skilled craftsman lays down a bead to weld the baffle.

Protection for your radiator: The Nomex Honey Comb Protector, sold by Speedway Motors, offers excellent protection from mud clods, rocks and stones. This is the same stuff the Outlaws use. It’s lightweight but very strong, at ½” thick. Place it directly in front of radiator and let it take the beating instead of your aluminum radiator. Some guys have raced a whole season with one honey comb. Usage will vary depending on track conditions. It can easily be cut down to size.

AFCO Radiator with Speedway Motors Honeycomb Protector

Sources

AFCO Racing
Phone: (800) 632-2320
Stewart Components
Phone: (906) 789-2816
Speedway Motors
Phone: (800)979-0122

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