As the name suggests, an internal combustion engine creates heat. The enormous potential energy from a few droplets of gasoline compressed and mixed with oxygen and a little spark helps propel us racecar drivers down the track, hopefully pushing us in front of our competitors. During this process, and especially at 6,000 rpm, all of this internal combusting starts to create an immense amount of heat. Too much heat starts to become a problem when temperatures go beyond the abilities of the engine itself.
Remember a steel engine block is just cooled off melted iron ore that has been cast into the shape of an engine. Bring enough heat to the party and you will find yourself in the meltdown zone. The good news is engineers already have solved this problem for us by creating a cooling system for engines: heat exchangers called radiators. These radiators use water to keep engines cool.
But if you remember anything about your seventh grade science class, you know that water boils when heated to 212 degrees Fahrenheit, or 100 degrees Celsius. It goes from a liquid to a gas. Essentially it becomes steam. Water cools engines, steam does not. As race engines go beyond 212 degrees, this becomes a big problem. But, in reality it isn’t a problem at all because of two things: antifreeze and pressure.
Your daily driver has coolant inside the engine/radiator that is 50 percent water and 50 percent ethylene glycol, commonly referred to as antifreeze. This simple 1:1 mix of water and ethylene glycol raises the boiling point of water up from 212 degrees Fahrenheit to 226 degrees Fahrenheit. Now we are getting somewhere. Except, actually, we are not. You see, NASA racers are not allowed to use ethylene glycol because of Club Codes & Regulations section 15.18 Engine Coolant, which says, “Glycol-based antifreeze and other additives that may cause a slippery condition if spilled on track are prohibited.” Yup, antifreeze on a racetrack is slipperier than moose snot and it’s hard to clean up … therefore you can’t use it. That means your boiling point is back down to 212 degrees, and if you live at high elevation, like Denver, believe it or not, your boiling point is already down to 208 degrees. We need pressure to solve this issue.
Here is the good news. For every 1 pound of pressure added to a system, the boiling point of water increases 3 degrees Fahrenheit. Engine cooling systems are pressurized to allow for this increase in the boiling point for water. The amount of pressure is regulated by the radiator cap. To demonstrate how the math works, imagine you have a vehicle with pure water in the radiator with a 10 psi radiator cap. Since 1 pound of pressure raises the boiling point by 3 degrees, then a 10-pound cap would raise the boiling point by 30 degrees. Instead of the water boiling at 212 degrees Fahrenheit, it would boil at 242 degrees. Nice! Now we can run hot!
Upgrading The Cap
A simple and inexpensive cooling system upgrade to any track car is to replace the OEM radiator cap with a higher-pressure-rated radiator cap. This will allow temperatures in the engine and cooling system to increase to a higher temperature before boiling the coolant and causing a big steaming mess under the hood. To choose the correct upgrade to a radiator cap, you first need to understand what your car came with from the factory. Radiator cap ratings aren’t always created for us dumb Americans. We understand things like 13 psi, which is the exact rating a 1990 Acura Integra came with from the factory. However, that radiator cap indicated the rating was 88 kPa which meant nothing to me. It turns out kPA represents kilopascals, which, again, doesn’t switch a darn thing on in my brain to anything useful.
The simple conversion from psi to kPA is 1 psi = 6.89475729 kPa. OK, that seems simple enough. I have a calculator on my cellphone, but things get murkier the further you look into this radiator cap thing. You mostly will see a rating of “bar” on radiator caps. Bar is the metric unit used to measure pressure. The metric system loves the number 100, thus 1 bar = 100 kilopascals. Here are some examples of commercially available radiator caps, their bar rating and their equivalent psi rating: 1.1 bar (16.0 psi), 1.3 bar (18.9 psi), and 1.5 bar (21.8 psi).
For our Honda Challenge 4 car, we wanted to increase the boiling point of our coolant, so we used a Mishimoto radiator cap rated at 1.3 bar, or 19 psi. Using the math that shows for every additional pound of pressure we increase our boiling point by 3 degrees we went from 212 degrees Fahrenheit — water’s boiling point at sea level — to 269 degrees Fahrenheit. That is a pretty easy upgrade that cost less than a tank of gas and took a total of five seconds to replace. We not only replaced our radiator cap, but we also replaced our OEM copper-brass alloy radiator with an all-aluminum Mishimoto drop-in unit.
Since we can’t use ethylene glycol in our radiator, thanks to CCR rule 15.18, then we are left with the obvious alternative of water. But just grabbing the hose outside of your garage and filling your radiator with tap water is not advised. This has nothing to do with the conspiracy theory about fluoride in drinking water having mind-control properties and taking over your car. This has to do with minerals in tap water that can harm your cooling system. Minerals create hard water deposits inside your radiator and water pump, which, can clog things up over time. To avoid putting these sorts of minerals inside your engine, you can use distilled water. Distilled water is created by boiling water and then condensing the collected steam back into a liquid. This process removes impurities and minerals from the water, which then won’t end up in your cooling system. A gallon of distilled water will set you back less than a dollar. This is a dirt-cheap upgrade, so it is an easy choice to make.
For our Honda Challenge 4 car, we took all of these deep dives into radiator caps, boiling temperatures, unit conversions, radiator types, and water distilling and decided to slap in a new Mishimoto all-aluminum radiator, a new lower-temperature thermostat, a higher-pressure radiator cap, a few gallons of distilled water and some silicone hoses. This combination of parts easily bolted into our 1990 Acura Integra RS and gave us the peace of mind that we would never have to think about this stuff ever again. Nobody wants to do more math than they have to.
We went with the upgraded aluminum radiator, because by increasing the pressure to the cooling system with the upgraded radiator cap, we were not convinced our 30-year-old copper-brass alloy radiator could withstand the higher pressure and the beating road racing cars with stiff suspensions take on the racetrack. We looked at the system as a whole, as opposed to looking at just one component, which is important to do when doing any modification to a car.
As a team who races with NASA predominantly in Southern California, keeping our internal combustion engine cool is important to us at tracks like Willow Springs and Buttonwillow. Think, hot desert. Our Mishimoto components should get the job done. And now you know what a kilopascal is.