A turbocharger can help remedy this situation. It’s not the complete answer, however, because the turbo’s compression action heats up the intake air, which results in a loss of density and consequently some engine power. An intercooler will solve the problem, but it is an expensive extra and cannot always be justified.
The sober fact is that an intercooler brings benefits, but also has some disadvantages. Its cooling effect enables the engine to inhale a greater mass of air per second and, when this amount of air is combined with the correct amount of fuel, the result will be an increase in torque, which leads to an increase in power. This extra power has two opposite effects: if the vehicle is used in a manner that was within its abilities before the fitting of an intercooler, the required power will be delivered at a smaller fuel control setting, resulting in an improvement in fuel consumption and a lower exhaust gas temperature.
However, if the driver exceeds the previous performance limits, for example by accelerating faster or cruising at a higher speed, then the extra power being developed must, inevitably, lead to an increase in overall fuel consumption, as well as an increase in stress on the engine components. If the pistons, connecting rods and crankshaft can take the extra stress, then all is well; if not, then engine damage may occur.
We recently tested a Toyota Hilux 3,0 KZ-TE 4×2 double-cab fitted with an intercooler developed by Steve’s Auto Clinic (SAC). The intercooler is fitted underneath the engine, away from the hot underbonnet air, and is a very sturdy aluminium casting. The computerised engine settings were optimised by means of a programmable Unichip, developed by Pieter de Weerdt of Pretoria. These chips enable a competent technician to alter the engine settings, either to get a new engine to perform as designed, or to change the settings after a modification.
Unfortunately, an unmodified double-cab 4×2 could not be found in time to make a direct comparison, but we were able to obtain a 4×2 single-cab, which was loaded with weights to make up the difference. For the purpose of the comparison, it was assumed that the aerodynamics would be very similar, especially at speeds below 100 km/h. It should be noted that the weight of the single-cab vehicle was set at 30 kg less to allow for the weight of the intercooler unit.
These results show the improvement that can be expected with the Steve’s Auto Clinic conversion. It is noticeable that the SAC vehicle shows relatively little improvement in the lower speed ranges, but a big improvement once it goes past 80 km/h. It stands to reason that, at low engine speeds, the turbo is not working very hard, so the intercooler cannot really come into its own. However, the modified engine mapping must also take some of the blame.
The test vehicle was fitted with an instrument that measures the exhaust gas temperature at the manifold by means of a thermocouple mounted about 100 mm from the cylinder head, before the air gets to the turbo. A readout mounted on the steering-column reacts instantly, and is fitted with a warning light and buzzer to warn if the exhaust gas temperature exceeds a preset limit. This is necessary because turbocharged diesels tend to develop high exhaust gas temperatures if driven at large throttle openings, such as when pulling a caravan up a pass in a high gear.
The difference between the control vehicle and the SAC conversion was immediately apparent. The intercooled vehicle felt livelier and could cruise at higher speeds. Overall fuel consumption, measured in mixed city and open-road driving, was an eye-opener. In fact, the conversion imparts a sporting air to a vehicle that is normally quite staid. Unfortunately, it is not possible to determine how much of the extra power is thanks to the intercooler and how much is due to the revised engine mapping.
The intercooler and the Unichip nullify the manufacturer’s engine warranty, but Steve’s Auto Clinic substitutes its own warranty. The intercooler fitment costs R6 900; the Unichip and optimisation costs an additional R2 500. If both fitments are done together, the total cost will be R8 900 and the conversion will take two days.