What is chiptuning?

Every modern car has an engine control unit, or ECU. Hundreds of times per second it decides how much fuel is injected, when ignition happens, and on a turbo engine how much boost pressure is built up.

Those settings live in a file. Chiptuning means reading that file out, adjusting it and writing it back. Often that can be done through the diagnostic socket under the dashboard; on newer cars the unit sometimes has to be opened up.

A manufacturer doesn't set an engine up for maximum output. It keeps margin for poor fuel, extreme temperatures, overdue servicing and differences between countries. On top of that, the same engines are often sold in several power variants — purely through software.

That margin is what chiptuning uses. Not by pushing the engine past its limit, but by sharpening the calibration within what the hardware can take.

In practice you mostly notice more pull at low revs. The car feels livelier and you shift down less often. The difference is more in the torque than in the peak power.

How much exactly varies a lot. A turbo diesel generally has more room than a naturally aspirated petrol engine. The software version, the condition of the engine and the fuel used all play a part too. Anyone promising a fixed percentage without knowing your car is guessing.

Chiptuning doesn't turn a bad car into a good one. If servicing is overdue, the turbo is leaking, or there are fault codes stored, more power only makes that worse.

The same goes for a worn clutch or an automatic gearbox that already has shifting problems — more torque is not what you want. A decent tuner looks at that first and says so when something is better left alone.

Report the modification to your insurer. If you don't, cover can lapse in the event of a claim. If the car is on lease or finance, you need the owner's permission.