Cooling Tips and Tricks

Intercoolers

Simply stated, heat is the enemy. An intercooler is a small radiator that cools the air after the turbo has compressed it. Since compressing air always increases its temperature, we have to find a way to reduce the charge air temp in order to get the most power out of it. There are a couple of styles of intercoolers commonly used. There is air to air, and air to water intercoolers. Air to air is simply a radiator that uses outside air temperature to cool the charged air inside using a series of tubes and vanes like the heater core in your car. As the outside air flows across the intercooler, it carries some of the heat of the charged air inside with it by convection. A air to water intercooler is similar except that it uses the cars cooling system, or a separate system, to help cool the charged air. It does this by using small water tubes along side the charged air tubes, as well as outside air flow, to cool the charged air.

The temperature of charged air (already compressed) increases as boost is increased. Temperatures can range from under 120 degrees to over 250 degrees depending upon the boost (measured in lbs. per square inch), and outside air temperature. A good air to air intercooler can decrease the charge air temp by as much as 70 degrees or more. Obviously, the larger the area of the intercooler (number of rows, width, height), the more heat can be extracted from the charge air. There is a trade off however. The more heat that is removed from the charged air, the more pressure is lost. This is because cooling a gas such as air, lowers its pressure. For that reason there is always a pressure drop across an intercooler. Pressure drop is not a terrible thing as long as the system is matched as closely as possible. Since boost readings are generally taken after the intercooler, what boost you see is what you are actually getting.

You can help your intercooler do its job by following some simple rules, the most important is to supply the coldest air to the air filter possible. Routing a fresh air duct and or isolating the air filter assembly from under the hood heat gives you an extra advantage to keeping charged air temps lower. Also you must keep the intercooler clean, and all of its fins straight and unobstructed. Move anything that blocks the intercooler, or consider relocating the intercooler itself to get it the coolest air possible with the least amount of deflection or obstruction.

Running no intercooler at all is not a real option if you are going to make real horsepower. The higher temperatures lower the amount of boost that can be generated. This is because the higher the charged air temp, the more likely detonation will occur inside the combustion chambers, and the hotter the engine will run. This becomes a vicious cycle that gets worse as more power is made. Even with computer controls, it is just not possible to make the same survivable horsepower without a good intercooler.

More Cooling

Yeah, I know, the factory put that 195 degree thermostat in the car for a reason. Unfortunately, the reason was more for emissions than for performance. Ideally a water temperature of 160 to 165 is best, but in the real world 185 to 190 is about average in a well built engine. Again, the colder the better, within reason. The water temp for normal operation is very important in a turbo engine. There are some tradeoffs that need to be made here also. Most turbo cars like a thermostat of 160 to 180 degrees. I like using a 160 personally, but you need to consider winter time driving and heater operations. Some cars won't produce heat in the winter with a cold thermostat. It's a matter of knowing your car and watching the normal temperature and then making a decision.

Never remove the thermostat all together and run the car. I can promise you'll have overheating problems. This is because the thermostat slows down the flow of water in the cooling system giving the radiator time to take heat out of the water. Without a thermostat, the water moves through the cooling system too fast for the radiator to extract much heat. It takes time to draw heat from a substance, and a thermostat gives your radiator the time it needs to cool the water. It also takes time for the water to absorb heat from the head and cylinder walls in the engine. So by slowing the flow down with a restriction like a thermostat, the cooling system gets improved efficiency due to more time to absorb and dissipate heat.

Knowing when to run your car hard is also important. Night time is cooler than day, so you have more options. Generally, you always have more options in boost settings when the outside temp is lower. Cooler air is more dense (heavier), and can make more power. Anything you can do to keep air temperatures down will be paid back by increased power, and more reliability at high RPM levels.

You can take that paragraph above and apply it to several modifications. One effective modification that doesn't cost a lot is to install a squirter so that it sprays a small fine mist across the intercooler. It can be activated by a hobbs switch controlled by boost pressure, or manually. It must not dump enough liquid to interfere with traction in any way. Stop now and read that line again.

Consider a Mitsubishi Eclipse that uses an intercooler mounted in front of a driven wheel, now consider what happens if you dump a water and alcohol mixture onto a tire trying to fight for traction. For these applications we form a catch pan and route a drain to a safe position. The idea is to deliver enough mixture to cool the intercooler, but not enough to make it to the ground. We also use a mixture of at least 50% alcohol so that it evaporates quickly. Ideally there is no run off, but there normally is a small amount. Drains should be run to as close to the centerline of the car as possible so that any drainage occurs between the track of the tires.

Another cooling related modification that drag racers have been using for decades is a cool can. This is basically a large coffee can with aluminum fuel line spooled inside of it against the wall of the can. Wrap the outside of the can with thin cork sheet, you can get it from parts stores as cork gasket material by the roll. We use bulkhead connectors drilled through the can to connect it into the main fuel supply line. Put a radiator type drain plug in the bottom of the can.

Now you can install the cool can into the main feed line to the injector rail. We feed the line from the gas tank into the top fitting, and the line to the injectors from the bottom fitting. When you are at the track, or out looking for action on the street, fill the can with ice from the top and snap the plastic lid back on. We add about 4 ounces of rubbing alcohol also to make a colder solution.

This reduces the temperature of the fuel which in turn cools the air charge in the cylinders when it is injected. Again this allows you to produce a bit more boost and horsepower. There are several companies that make cool cans, so check with a local speed shop if you don't feel like playing handyman.

Go to a colder spark plug. This belongs in the ignition section right?  WRONG! The idea behind running a colder plug is nothing more than keeping the engine from detonating for as long as possible. That means keeping the temperatures down in the combustion chambers. The colder the charged air coming into a combustion chamber is, and the longer it can stay that way, the more expansion potential it has. That means more compression or boost can be run to produce a more powerful explosion.

Ideally the combustion chambers could be 200 degrees or lower each time the intake valve brings in a fresh charge or air and fuel. Unfortunately this doesn't happen in the real world, but you can make it better by keeping the spark plug from glowing red hot between firings. A hot plug or any sharp ridges in the combustion chamber or piston tops will heat faster and retain heat longer. This can lead to detonation or even spontaneous combustion as the fresh intake charge is drawn into the chamber.

In short, about anything you can do to reduce intake air temp, and running temp, is a good thing. Maintaining those lower temps is also desirable. Wrapping intake tubes and intercooler plumbing as well as fuel lines to keep under hood temperatures out is also worth considering.