Pit Talk

When most people think about intimate activities, they usually imagine private interludes of hugs and kisses. Yet intimate associations are very common in race cars: rings have intimate contact with the cylinder walls; head bolts have intimate contact with the block; and valve guides have intimate contact with the cylinder head. Even the activities between systems are intimate: As the piston rises in the bore, gas pressures build; it is hoped that one, and only one, flame front will be ignited; energy is released; and the piston is shot back down the bore with great force.

Race engines are similar to other intimate activities in that they create heat, which can be a friend or foe to drag racers. Engine builders, and a few drag racers, have been studying the thermal balance within an operating race engine, but the majority of drag racers are unaware of the importance of heat management.

For example, the engine and transmission act like a thermal bank when they are warmed; they receive and store a good amount of heat energy. This leads to a point where the entire engine and transmission have reached their optimum operating temperature. When this happens, the temperature is said to be normalized. The important point for drag racers is that the engine will run more consistently if the engine and metal temperatures are at a standard optimum level, but most racers don't understand that it can take three runs to normalize their engine temperature.

Collectively, we don't pay enough attention to the temperature conditions of our race crafts. Many racers don't monitor oil versus water temperature, and most don't have a temperature gauge for their transmission.

Let's carry this issue further. Manufacturers and engine builders don't all agree on the best method to cool an engine. One old trick was to trim the impeller blades on the stock water pump to slow the flow of the water. This gives the water more time to loiter in the radiator but doesn't help cool the water jackets in the cylinder heads. Other people use high-flow pumps, then restrict flow to create back pressure in the system. Another trick is to pressurize the cooling system so the boiling point, which is also known as the vapor point, is raised. Water boils at 212 degrees Fahrenheit at atmospheric pressure, but this can be increased as high as 270 to 280 degrees with a pressurized cooling system, using a 24-pound cap.

With these conflicts of opinion in mind, I would like to introduce a new line of thought about intimate contact and how it affects heat management and power production. The following concept was developed by Evans NPG Cooling Systems, (860) 364 5130. It's water-free and is not pressurized.

According to Evans Vice President and Manager of Engineering Steve Pressley, the heat at the top of the combustion chamber is not even. Hot spots form within the chamber, and the coolant boils on the water-jacket side of the head (left). It there is a wide temperature differential between the coolant temperature and the boiling/condensing temperature of the vapor bubbles, the bubbles will recondense and carry heat away from the combustion chamber, shedding their heat to the coolant as they recondense.

If the temperature difference is minimal, the bubbles won't recondense; they will remain blanketed to the metal surface around the heated area, permitting it to get hotter (left). The incoming coolant will not have any intimate contact with the heated areas because the surface bubbles are blocking the way. Hot spots develop, detonation increases, then parts break in sometimes violent fashion. "When that boiling begins to take place," Pressley said, "there is a phase shift, and the properties of water start to fall off while the properties of NPG [nonaqueous propylene glycol] start to maintain themselves or actually improve."

This leads to the heart of the Evans system. Instead of water, the coolant is NPG, which has an atmospheric boiling point of 369 F, versus 212 for water. NPG, with its higher boiling point, will enter a hot water jacket, and because there is a big temperature differential between the engine-coolant temperature of the NPG and the vapor bubbles, the bubbles will recondense and the blanket of vapor never forms. The intimate contact between the coolant and the heated metal is retained 100 percent of the time.

When hearing about this technology, I was impressed with the balance of the system, which has three components: coolant, radiator, and pump (left). Jack Evans, company founder and inventor of this process, studied coolant volumes and flow rates through the engine and the radiator. Each component has its own development story. With the first problem solved, a replacement for water, Evans looked at radiator configuration.

Pressley said, "Once we have the thermal-management problem solved on the engine side and have eliminated the detonation problem associated with that, the actual operating temperature of the system is dependent on the flow rate and the radiator. The [ribbon-shaped] radiator tubes are only .100-inch tall, then an inch wide; the wall thickness is only .017-inch. Many people with heat problems add rows of tubes in their radiators. These rows are front to back, then stacked with fins between them.

"All a bigger radiator does is delay the problem, but people began making them thicker and thicker. Then the radiator has a greater density. Recently, the fin density has gotten smaller as the radiators got thicker. What we do is balance the two depending on the tube and core size, the number of tubes, [how they are] stacked and the actual fin to air [ratio] in square inches, the fin to tube contact, and the tube to air. Then we know what the total tube surface area is. We also know what the liquid side contact is with the tube [and from there we can] figure out these [heat] transfers."

With this balance of flow and thermal transfer in mind, Evans designed a pulley-driven water pump (left) that flows 120 gallons per minute at 6,000 rpm. The diameter of the impeller is larger than most, simply to get the high volumes without spinning the pump too fast. Early work included using higher-speed stock pumps, but as pump rpm increased, and they were doubled in some instances, bearings, accessory drives, and belts failed at a higher rate. Keep in mind, the system is ideally not pressurized. In fact, a vent on the radiator cap forbids rising coolant pressures. This has some strong safety implications. With no coolant pressure, the driver is less likely to get sprayed with superheated coolant during a crash. When a system is pressurized, Evans recommends using only a 4 to 7psi radiator cap; none higher is needed.

I realize that many racers feel they have an intimate relationship with theirs mechanical partner, the race car. But is this so? Remember that we need to have a standard engine and transmission temperature when we race, but many rounds are lost because the engine and transmission only got to their normalized temperatures after the third run, which is often the first round of eliminations at a bracket race. Imagine the startled racer who after breaking outs asks, Did anyone else pick up? Often the answer is no. Developing a normalized engine temperature is what those oil pan heaters are all about, so some racers are on the ball.

Yet many will question some aspects of this technology. For example, if hot spots can be kept under control, detonation can be managed better also. We all may have to update our philosophy regarding the intimate relationship. between heat and power production. Evans and Pressley imply that their system will not only provide consistent heat management throughout a day of racing, but because hot spots are eliminated and detonation is under control, racers can run their engines at higher temperatures and make more, not less, power.

I look forward to comments on this idea.