How an Intercooler works
What is an intercooler?
An intercooler is an intake air cooling device used commonly on turbocharged and supercharged engines.
What does it do?
Intercooler cools the air compressed by the turbo/supercharger reducing its temperature andf increasing the density of the air supplied to the engine.
How does it work?
As the air is compressed by a turbo/supercharger it gets very hot, very quickly. As its temperature climbs, its oxygen content (density) drops, so by cooling the air, an intercooler provides a denser, more oxygen rich air to the engine thus improving the combustion by allowing more fuel to be burned. It also increases reliability as it provides a more consistent temperature of intake air to the engine which allows the air fuel ratio of the engine to remain at a safe level.
There are two types of intercoolers; Air-to-Air and Air-to-Water.
An Air-to-Air intercooler extracts heat from the compressed air by passing it through its network of tubes with cooling fins. As the compressed air is pushed through the intercooler it transfers the heat to the tubes and, in turn to the cooling fins. The cool air from outside, traveling at speed, absorbs the heat from the cooling fins reducing the temperature of the compressed air. This system's advantages are simplicity, lower cost and light weight.These factors make it by far the most common form of intercooling. The down sides can be a longer intake length (as the intercooler is usually at the front of the car) and more variation in temperature than the Air-to-Water type.
An Air-to-Water intercooler uses water as a heat transfer agent. In this setup cool water is pumped through the air/water intercooler, extracting heat from the compressed air as it passes through. The heated water is then pumped through another cooling circuit (usually a dedicated radiator) while the cooled compressed air is pushed into the engine.
These intercoolers (also known as heat exchangers) tend to be smaller than their Air-to-Air counterparts making them well suited to difficult installations where space, airflow and intake length are an issue. Water is more efficient at heat transfer than air and has more stability so it can handle a wider range of temperatures.
On the downside the Air-to-Water system is complex, heavy and has the added cost of a radiator, a pump, water and transfer lines. Common applications for these are industrial machinery, marine and custom installs that don't allow the easy fitment of a air to air, such as a rear engined vehicle.
The best placement for an air to air is in the at the front of the vehicle. The “front-mount” is considered to be the most effective placement.
All Mitsubishi Evos come with a factory front-mount intercooler.
When the engine layout, or type of the vehicle do not permit the “front-mount” placement, an intercooler can be mounted on top of the engine, or even on its side, but these are not considered as effective as the air flow is not as good and the intercooler can suffer from heat soak from the engine when the external airflow drops. These placements will often require additional air ducts or scoops to route the air directly into the intercooler.
Subaru's trademark top-mount requires a scoop in the bonnett to route the airflow onto the intercooler.
The Air-to-Water system can be mounted anywhere in the engine bay, as long as the radiator is mounted in a position with a good airflow, and/or with a thermo fan attached to it.
If your car doesn't have a factory intercooler there are plenty of aftermarket kits available.