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Helping boosted engines keep their cool

Turbocharged and supercharged cars usually go like stink; but is the one you’re thinking of buying missing an ingredient that’s as important as the right sauce on a burger?

That would be an intercooler – a “radiator” that cools air, not water. An intercooler can provide significant extra power and torque – the larger the cooler the more it gives – and once installed is basically maintenance-free.

Yet some manufacturers of turbo vehicles don’t include an intercooler, so you’re missing a good whack of extra performance.

There are several reasons for leaving the sauce off the burger.
One is cost; another is insurance considerations that prevail in the country of origin. Or it might have to do with reliability issues; the engineers may not be confident that the upgraded motor will stand up over years of use.

Fortunately, adding an intercooler is not difficult for people who know what they’re doing, so long as there’s the physical space for it. However, cooling isn’t cheap, may attract higher insurance premiums and may require Low Volume certification.

Because in intercooler-world, bigger is better, some owners of factory-intercooled vehicles like to ditch the small stock job and fit a larger one.

This is exactly what Auto Adviser did years ago on a turbo-intercooled diesel, replacing the fist-sized factory item with the biggest piece of intercooler real estate that would fit behind the grille. The job also included recalibrating the fuel pump, but nothing else.

The reason was not to hoon down Main Street but to dip into the well of torque that intercooling can offer for off-road driving.

In before and after dyno testing, torque at the wheels increased by 46 per cent in fourth gear and kilowatts rose by 28 per cent. A pretty convincing argument for some extra plumbing work.

A turbocharger works with a diet of hot air, which is less efficient than cool air. Power and torque are proportional to the amount of air entering the combustion chamber, mixed with the right amount of fuel.

Cooler air allows a higher mass to enter the combustion chamber. A typical temperature drop is in the range of 35 degrees C and 40 degrees C, depending on the ambient temperature. It’s as simple as that.

Well, not quite as simple. Doing an intercooling job just right requires skill and knowledge.
Two main things make an intercooler work well.

One is its internal flow characteristics, with few tapered bends and no internal welds to cause turbulence.

The other is the cooling fins, which should have a large and well designed surface area. So the quality of the hardware is a major factor. There’s also the matter of where to mount the intercooler for best effect.

Intercooler proponents claim better reliability and reduced fuel consumption. The fuel economy claim comes from the efficiency of extra power and torque for the same engine capacity, and the lower operating temperatures that will cause less friction.

However, tweaking of the fuel delivery system, often carried out in conjunction with intercooling, will negate any fuel saving advantage. Auto Adviser’s vehicle uses about half a litre more per 100km than it did before the upgrade.

Intercooling will provide cooler exhaust temperatures, which could have favourable longevity implications for the turbo – it’s said to be one of the best ways to prevent failures – cylinder head(s) and pistons.

Although usually associated with turbochargers, intercoolers work well with superchargers and various companies – often American – specialise in developing kits. Even Garrett, one of THE big names in turbocharging, has a kit for superchargers that bolts between a vane-type supercharger and the intake. There are plenty of intercooler kits for centrifugal blowers, of the type fitted to V6 Holdens.

Adding an intercooler isn’t the ultimate step. Some cars have a nozzle to spray the intercooler with water to further reduce temperature. They do this automatically, but there’s a manual over-ride for when the driver really wants to give it a shower.

Auto Trader New Zealand