Superchargers and Intercoolers

An intercooler is not a performance part per se, so I've often head car enthusiasts say do superchargers need intercoolers if it doesn't boost power? Well, as is the case turbocharged cars, an intercooler performs a fundamental and important role in maintaining the reliability and longevity of a supercharged engine. You can think of an intercooler as a radiator that cools the compressed air (intake charge) that the supercharger pumps into the intake manifold. Its main purpose is to cool the intake charge. Reducing the temperature of the intake charge has two benefits: it makes the intake charge denser and denser air produces more power as it has more air molecules per cubic inch; and it reduces the possibility of detonation.

There may be two types of intercoolers on the market — air-to-air and air-to-water intercoolers but, although air-to-water intercoolers work wonders on extremely short runs and are ideal for drag cars, they are not practical on street- and endurance type racing cars. For street- and endurance type racing cars you would need to use an air-to-air intercooler. Unfortunately, an air-to-air intercooler has one major disadvantage: it is an obstacle in the intake charge path and causes a drop in boost pressure! Although there is no way of getting around this problem, the benefits of having an intercooler far outweigh this disadvantage. The best you can do is to maximize the efficiency of the intercooler and minimize the pressure loss caused by it rather than using a supercharger without an intercooler.

You can minimize the pressure loss caused by the intercooler by designing efficient intercooling systems that to keep pressure loss at a minimum. Firstly, you should use a plate-and-shell core rather than an extruder core as the plate-and-shell core offers less resistance to air flow. Secondly, the internal flow area of the core has a major affect pressure loss. Therefore you should select an intercooler with the correct internal flow area in order to keep pressure loss at a minimum. The following graph is a good tool to estimate the required internal flow area based on your supercharger's flow rate.

Internal core area to flow rate

As you can see on the graph, a supercharger that produces a flow rate of 300 cfm requires an internal flow area of approximately 15 sq in. Once you have estimated the internal flow area your supercharger requires, you can determine the actual core size that you need. This can be a bit tricky as only about 45% of the intake charge will come into contact with the heat exchange elements of the intercooler core. Therefore you must first divide the required internal flow area by 45% then divide the result by the core thickness. This gives us the following formula:

internal flow area ÷ 0.45
core thickness

Thirdly, you need to remember that every subsequent inch of core thickness is 40% less effective than the previous inch as the temperature of the ambient air flowing through it increases as it takes heat out of the intake charge. Thus, using an intercooler with a thinner core but a larger fontal area would be more efficient than a thicker intercooler with a smaller frontal area.

Fourthly, you can also improve the cooling efficiency of your intercooler by fitting a duct to the frontal area to force ambient air through the core. Without a duct, approximately 25% of the ambient air will pass through the core and the rest will follow the path of least resistance around the core. With a more efficient intercooler, you can increase boost pressure to offset the loss of pressure caused by the intercooler.