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Watching AStPW’s (successful!) solo crossing of the Kalahari in Episode 3 of his new TV series – Take a Deep Breath – triggered an issue which I had pondered for my own vehicle, regarding engine power increase by means of chipping.

Andrew cuts over to the workshop, and explains the installation of a low-pressure (0.6 bar boost) turbo to his vehicle, mentioning that the supplier is confident that the engine life will not be affected. For Gautengers this makes even more sense, as the first 0.15 – 0.18 bar will be used purely to restore the vehicle performance at reef altitude to that specified at sea level, effectively only increasing inlet manifold pressure by 0.45 bar above standard.

I have previously posted my thoughts on this matter on a UK motoring forum and was accused by one reader of being alarmist. I have attempted to clean out the bits that could be regarded as such, but if some readers still find it so – it is purely unintentional. The sole purpose is to spread awareness.

A number of adverts for increasing engine power through chipping, especially on turbo-engined vehicles, appears regularly in the back pages of most SA automotive magazines. Results are good for relatively low cost, and from one of the advertiser’s website, the following performance increase is claimed:

The concern for most people considering chipping seems to be the reliability of the engine, and if it fails, the warranty implication. The general consensus is also, that if the extra power is used sensibly, this should not adversely affect engine life.

Unfortunately the longevity of the engine is not the full story.

Using the Freelander ll as an example (purely because the relevant technical information is freely available off the internet), the following argument:

Consider the 2.2TD4 Auto, and for the purposes of demonstration, only the torque, which on the standard engine is 400Nm max. This power is available at the crankshaft driving the transmission, which is an Aisin (52% owned by Toyota) TF-80SC, with a max torque transfer capability of 440Nm – thus a 10% margin of safety. Next, increase the torque of the engine by the same 28% (as for the Golf TDi, above) through chipping, and the transmission must now transfer 512Nm from the engine to the gearbox.

This means that at maximum torque, excessive slipping of transmission internal components will generate friction, and if not initially causing mechanical wear, will under constant use increase the temperature of the ATF, possibly beyond the viscosity range – after which the wear will commence. Some cars have transmission oil coolers to prevent exactly this under heavy loading conditions, e.g. towing.

Next, the torque is transferred to the wheels by a Haldex differential. The unit in the Freelander ll is the GEN lll version, good for 1500Nm of torque transfer. This sounds like a lot, but the torque input to the differential is increased by the same ratio as the gear selected. 1st gear on the Aisin transmission has a ratio of 4.148, so the 28% torque increase from the chipped engine now delivers 2124Nm to the Haldex. The limitations on the Haldex is determined by the friction coefficient of the clutch, which in turn is determined by the number and surface area of the clutch plates and the pressure exerted by the actuator. The clutch plates are in direct contact with each other when the Haldex is locked to drive all 4 wheels, depending on the traction control mode. Some SUVs always move off in 4×4 and only switches to 4×2 once it has gained momentum.

Until the static friction of the Haldex is overcome (after which slippage occurs) the momentary torque through the final drive of 3.3 translates to 7009 Nm to the rear axle. As the traction control can theoretically transfer all the torque to one wheel should e.g. the front axle and one rear wheel be slipping, all this torque will be applied to one halfshaft. Once again, premature Haldex/CV joint wear will result, and if you can believe one post on a UK Landrover forum, turn into a literal “axle twister”.

Admittedly, this will probably only occur on a Sunday evening down Voortrekkers Rd or, when driving offroad, waiving the “using the power sensibly” advice in a panic situation, flooring the accelerator to induce more wheelspin just to be sure the traction control system gets a clear message of ”HELP!”, in order to brake 3 wheels and send all the torque to the remaining one.

From a drivetrain perspective, it therefor seems safer to chip a petrol engine (given it has the same transmission and differential as the diesel variant), as the safety margin is larger.

JJJ