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By Julian Edgar
Intercooler Mounting
When either increasing the size of a factory intercooler or installing a new one for a custom forced aspirated car, care needs to be given to the location that is chosen. The first point to consider is the amount of ambient heat that is present. An intercooler core absorbs heat just as well as it sheds it. This means that an underbonnet intercooler core can easily become an intake air pre-heater if care isn't taken with its location. Turbo cars run especially high underbonnet temps and so a bonnet vent designed for intercooler cooling while the car is under way can easily become a "chimney" ducting out hot air while the car is stationery - hot air that passes straight through the intercooler core. In fact, the behaviour of the intercooler while the vehicle is stopped is very important if you're in the habit of caning the car in traffic light Grands Prix!
By far the best location for an intercooler is in front of the engine radiator. The car manufacturer will have aerodynamically tested the vehicle to ensure that large volumes of air pass through the engine cooling radiator, and so an intercooler placed in front of that is sure to receive a great amount of cooling air. Note that the intercooler should be in front of any air conditioning condenser as well!
The air/air core should be ducted with the cold air if at all possible. Many people simply place the intercooler at the front of the car, hoping that the air being forced through the front grille will all pass through the intercooler. However, if there is an easier path for the air to take, that's the way it will go. Sheet metal guides can be used to channel the air coming in the grille through the intercooler, and foam rubber strips can be used to seal the escape routes that the air might otherwise take.
The plumbing leading to and from the intercooler should produce only a minimal pressure drop. Factory turbo cars often use intake ducts that smoothly increase in size from the diameter of the turbo compressor outlet (often only 50mm or so) to the inlet diameter of the throttle body (perhaps 80mm) and if this can be done, it's an approach which should be followed. Intercooler plumbing should have gentle curves and be as short as possible. Don't forget when you are planning the plumbing that the engine (and so also the blower or turbo!) moves around, while the body-mounted intercooler core does not. This means that some rubber or silicone hose connections must to be incorporated in the plumbing to absorb the movement.
The return duct from the intercooler should be insulated to avoid it picking up heat from within the engine bay. Lagging the pipe with fibreglass or ceramic fibre matting works effectively without being too bulky. The pipework can be finished off with a wrapping of aluminium adhesive tape of the type sometimes used to seal roofs. Also note when planning the intercooler pipework that the compressor cover of a turbo can be easily rotated to allow the outlet to come out at a different angle. This can reduce the number and tightness of the bends required.
Some people believe that if they fit a very big intercooler with large ducts, the volume of charge air within it will unduly slow throttle response. Their concern is unjustified however - throttle response problems (for example, turbo lag) are largely the result of other factors within the forced induction system, not the volume of air within it.