Cooling System Basics by Peter Dozeman Some racers spend a lot of time and money building a hot rod engine only to get on the track and have to pull off early because the coolant gauge is threatening to melt the engine into scrap metal. Having spent all their time and money making more horse power, they may have overlooked the cooling system. More power generates more heat, period. Other racers decide to save money and buy a modern, fuel injected engine that runs on the ragged edge of lean and soon find out that again, more power is more heat. Whichever method is used to get more horsepower in your welter weight race car, the cooling system needs to be just as efficient as the new power plant. The radiator is the main component of the cooling system. It can be best explained as a heat exchanger. It takes the unused heat from the engine, via the coolant, and transfers it into the air. This is not an easy thing to do. There must be enough radiator fins to pull the heat out of the coolant. At the same time the fins must allow air to pass through, to get rid of heat, at varying air speeds and air flow conditions. Radiators for motorcycles are designed with the cooling fins spaced closed together because they have high, unobstructed air flow. The airflow on a motorcycle is seldom blocked by mud or tire rubber. For these reasons, a radiator that may keep an engine cool in a motorcycle may not be ideal for a welter weight race car. The Fluidyne Corporation uses an efficient combination of cooling fin density and tube spacing that delivers good cooling characteristics for welter weight race cars. (See figure 1). They use a very wide single row tube that out-cools three rows of conventional _" copper tubes. Also their fins are not as dense as OEM radiators to allow more airflow at lower speeds. Mud and rubber block air flow through the radiator. This problem is typically dealt with by installing complicated shrouds and screens in front of the radiator. These items do a good job of keeping the radiator clean, but may block the airflow. Air passing through the radiator is essential to transferring heat. The best way to address these problems is to install a well-designed fan and shroud. Bolting or zip-tying a round fan to a rectangular radiator is very inefficient. (Square-peg round-hole) The only area of the radiator that will be cooling is less than the diameter of the fan. The fan, in conjunction with a properly designed and installed fan-shroud will pull air through the entire core of the radiator, even when the air flow is partially blocked by a screen that is full of mud or rubber. The design and installation of the fan and shroud is very important. There must be no gaps or leaks around the fan or fan-shroud. Seal the smallest openings or leaks with either foam tape or silicon. Any gaps or holes will allow air to bypass the radiator core. The air wants to take the path of least resistance. It has to be forced through the cooling fins of the radiator. Figure 2 is a good example of a well designed fan shroud. The only compromise is the shroud should be deeper. Space constraints of a welter weight race car do not allow for it. Now that we have the correct radiator, fan and shroud installed, we need to consider the radiator cap. A radiator cap's job is not as simple as keeping the dirt out and the coolant in. A radiator cap holds specific pressure on the cooling system. Every pound of pressure held on the cooling system, will raise the boiling point of the coolant 2.5 degrees. Water boils at 212 degrees. If you add a 23 lb cap, the water will not boil until 269 degrees. It's important to raise the boiling point because once the coolant boils it will create pockets of steam in the engine. These pockets of steam only compound cooling problems. Once this happens, the coolant typically leaves the cooling system. Without coolant, it cannot cool. Even with all these precautions, occasionally the coolant must leave the cooling system to avoid bursting a hose or causing the radiator to leak due to extreme pressure. Where the coolant goes when it does leave the cooling system is very important. The coolant must go somewhere where it can be recovered. A coolant recovery tank is an essential element to a cooling system. It catches the coolant that is pushed out of the cooling system when the pressure exceeds what the cap is rated for. It needs to hold the expelled coolant so it may be drawn back into the cooling system when the temperature decreases and vacuum will siphon the coolant back in. I prefer keeping the coolant recovery tank cheap and simple. It's important to be able to see what is happening in the coolant-recovery tank. Fancy aluminum recovery bottles look good but I'm never sure whether or not the tank is properly designed because we can't see inside of it. All that is needed is some type of clear plastic drink bottle with the hose from the radiator filler neck to go completely to the bottom of the bottle. It's a good idea to cut the end of the hose inside the bottle on a 45 degree angle so it won't suck to the bottom of the bottle and prevent the flow of coolant back into the radiator. The coolant-recovery bottle needs a vent-hole in the cap so the coolant can siphon back into the radiator when it cools (See figure 3). Also, mount the recovery bottle as high as possible, so it's easier to siphon coolant back into the radiator when it cools. Now that we have a radiator with proper air flow because we have a fan and fan shroud that fit well, and we have a cap that will hold enough pressure in the cooling system and a recovery bottle that will catch any coolant that is pushed out of the cooling system and also draw back in. We need to discuss tubes and hoses. Cooling system installations on welter weight race cars are always custom. There are no off-the-shelf parts for each chassis and engine combination. The mechanic/fabricator has to find hoses and tubing to fit the application. Make sure that the metal tube which the hose slips over has some type of bead or raised portion so the clamped hose cannot slip off. This will prevent hoses from popping off tubes (See figure 4). "Low Buck Tools Inc" offers a bead-forming tool for tubes. This tool can form a hose bead on steel, brass, aluminum or copper tubing 5/8th inch o.d. and larger with a wall-thickness up to 0.065" This extra attention to detail will help keep your car in the race track and off the hook. |
RMDCRA
Rocky Mountain Dwarf Car Racing Association
RMDCRA
| Colorado |