Intercooler

Intercoolers have been used on turbocharged and supercharged engines for quite some time now. When used on a supercharged engine they are often called aftercoolers. Turbos are the most common usage for intercoolers though. Any engine that uses an air compressing device such as superchargers and turbos can benefit from intercoolers. When the air gets compressed it can heat up dramatically, up to 300 degrees F. This dramatically reduces the compressed air density and limits the maximum boost. The high intake temperatures can increase the chance of detonation in the engine, causing major engine damage. An intercooler can fix this problem.

 

Intercoolers are designed to cool down the heated intake air that comes from the compressor. Intercoolers are generally made in two different designs. The first and most popular type is the air to air and the other type is the air to water intercooler. There are a few alternative ways to cool the air which I will discuss at the end. The air to air has been most extensively used on mass production vehicles. They are similar to an engine’s radiator, and do a similar task. They are carefully designed to have smooth airflow inside as to not restrict the engine’s airflow. Outside the air moves across the aluminum fins and strips away the hot air. One of the biggest design constraints of an intercooler is the internal volume and cross sectional density. The more volume the intercooler has, the more turbo “lag” an engine will have. The “lag” simply means the delay time between when the gas pedal is pressed and the turbo starts to build considerable boost. Unfortunately you can not simply reduce the volume for two reasons. One, the cross sectional area must diminish, meaning less area for air to move across the fins. This could be accomplished with a thicker intercooler but then the air is already heat soaked by the time it reaches the back. The second reason is that the air has to be spread out through “tubes” crossing the intercooler. If there are not enough “tubes” the area becomes too small, and the boost is significantly reduced. Up to three psi of loss is standard on an intercooler. If you were to simply increase the diameter of the tubes, it would not be enough as the air in the center of the tube can’t release it’s heat into the tube wall. Most factory installed intercoolers are smaller to avoid high cost and turbo lag. That is why many people install larger intercoolers especially if their turbo boost has been increased. Another aftermarket alternative in air to air intercoolers is to spray water, with a remote valve, onto the intercooler. The Subaru Impreza WRX STI uses this with their front air cooler. The water transfers heat better than air and also helps cool as it evaporates off the intercooler. Speaking of better thermal conductivity (heat transfer) the air to water intercooler was designed exactly for this reason. It works in the same way an air cooler works internally. The outer of the water to air is covered in a “box” which circulates water around the internal “tubes” that run to the intake. The water cooler can have the same amount amount of air flow with a much smaller volume. This is because the heat conducts or moves into the water much easier. The heated water then moves through a pump and circulates through a small seperate radiator. Drag racers like this type because they can add a container of water inline and place ice in it before going down the track. This dramatically lowers the temperature. Another advantage is that the intercooler can be much smaller and can be placed anywhere. It dosen’t need to be placed in front of the radiator to be cooled as the air type does. Also it dosen’t need the large volume tubes that connect it to the front of the car. Some disadvantages would include price which can be almost double an air to air intercooler. Another problem would be heat saturation. If you continued to accelerate the water will eventually retain some of the heat and takes a little longer to cool it off. This is due to the volume of water being used. Alternative intake air cooling without adding volume can be accomplished, but is usually not as effective. Actually nitrous can significantly lower the temperature as it evaporates and decompresses, but is generally not used with a turbo because the tuning can get very tricky. Fuel supply and timing has to be exact or you will damage the engine. Another way to cool the engine is to spray alcohol into the intake air. This has the advantage of making the mixture slightly richer. It is not dangerous because it dosent require more fuel like nos. Although it dosen’t produce nearly as much power as nitrous, it is safe. It cools the air by evaporating and usually allows a few more psi of turbo boost.