Or it might have to do with reliability issues - engineers may not be confident that an intercooled motor will stand up to years of perhaps hard use.
Intercooler proponents claim not only more grunt but 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 lower operating temperatures that cause less friction.
Intercooling provides cooler exhaust temperatures which could lengthen the life of the turbocharger, cylinder head(s) and pistons.
Fitting an after-market intercooler is not difficult for those who know what they're doing. But cooling is not cheap, may attract higher insurance premiums and may require certification. Because in intercooler world, bigger is better, some owners of factory-intercooled vehicles like to ditch the small stock unit and fit a larger one.
This is what I did years ago on a turbo-intercooled diesel, replacing the little factory item with the biggest piece of intercooler real estate that would fit behind the grille. The job also included recalibrating the fuel pump.
The reason was not to hoon down Main St, but to dip into the deeper well of torque that intercooling offers.
Before-and-after dyno testing showed 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 usually 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 35C to 40C, depending on the ambient temperature.
Two main design considerations allow an intercooler to 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. There's also the matter of where to mount the intercooler for best effect.
Although usually associated with turbochargers, intercoolers work well with superchargers, and various companies specialise in kits.
Even Garrett, one of the big names in turbocharging, has a kit 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.
Some performance cars also have a nozzle to spray the intercooler with water to further reduce temperature. They do this automatically, but there's a manual override for when the driver really wants to give it a shower.
