Most race and rally engines are pushed for every last bhp, and thus they more common to fail, whilst normal car/van/lorry engines are limited back, well away from probability of multiple failures. Each individual engine is different as in how much it can be pushed in a remap, but a good remap from a quality tuner will never get close to the limits of component failure/

You will see that the top companies within the market place have all develop vehicle improvements to similar outputs. Beware of tuners who claim significantly more, it’s either lies hoping that the average customer wouldn’t be able to tell the difference, or the engine is being pushed too hard and will quickly become unreliable.

Sales and marketing also have a big affect on the way an engine is mapped. Low spec models often have the exact same engine hardware as the high spec models, often can be 50 BHP difference between them yet the only difference is software.

If you look in the manufacturer brochure at the engine specs, the torque graph will rise, then flatten out on a straight line, and then drop off. This obviously isn’t how an engine breathes, and it’s the request of sales and marketing to produce this flat lining of the torque. Why? Well it’s about having better torque figures than the competition and about local market taxation laws.

Some manufactures diagnostic equipment may detect a remap if they go looking for it, generally during a service it goes undetected, although some forward-thinking manufacturers turn a blind eye to a quality remap anyway.

The official line from most manufacturers is that if a modification causes a problem with the vehicle, then the part of the vehicle affected will not be covered; but this does not mean that they can disregard the entire warranty. If, for example, your vehicle’s central locking system failed, they would not be able to void the warranty because of the remap.

A remap alters the fuel, boost, and torque characteristics of the engine by adjusting the fuel pressure, injected fuel quantity, maximum permissible visible smoke limit, boost pressure, and torque limits.

The conversion offers a fully understood alteration to the engine characteristics, whilst still operating with complete feedback control, and within all preset engine sensor parameters.

These interfere with engine management signals to trick the injectors into adding more fuel, relying on the principal of more diesel equating to more power… which is correct, it does increase a diesel engine’s BHP. Crucially though, there is no control over the amount of black smoke coming out of the exhaust, and no thought is given to how other vital engine management systems are affected.

Too much smoke is undesirable, both environmentally and visually. The black smoke is unburnt diesel fuel with deposits exiting straight out of the exhaust pipe. This results in raised emissions, a higher thermal load on the engine, and poor drive ability – with “bucking” a common problem. It is clear what this means for your engine.

Because a diesel box operates independently from the other – increasingly complex – engine management systems, the results of using one can induce undesirable results.