What is overboost?

Feeling the pressure to know what overboost is? Let us explain

You may have heard the term ‘overboost’ being mentioned when referring to a car’s performance, but other than sounding cool, what exactly does it mean? Well, in very simple terms, it refers to a temporary increase in power in cars fitted with turbocharged engines.

In this article we go into detail about how this is achieved and what the benefits of the overboost function are in everyday driving.

How does overboost actually work?

To get a better overview of how the overboost function works, we need to take a quick look at turbochargers.

Most modern cars use small turbocharged engines to deliver the best of both worlds in terms of emissions/economy and performance. A turbocharger is powered by exhaust gasses, spinning up a turbine blade to force additional (clean) air into the engine, which allows more fuel to be burned, resulting in extra power.

The benefit of this over just using a larger capacity engine is that the boost levels can be electronically controlled, only delivering the extra power when you need it. That means lower fuel bills and more affordable running costs.

The term ‘overboost’ refers to when the turbocharger delivers an extra dose of boost for a short period. It is still operating within the manufacturer’s preset limits, so to be more accurate it should really be called ‘temporary extra boost’, but that doesn’t quite have the same ring to it.

One of the first production cars to use the overboost feature was the Ford Focus TDCI, it has also featured on the Ford Fiesta ST, VW Golf GTI Clubsport and Hyundai i30N, providing 10-15% more power and torque for up to 20 seconds at a time.

Does overboost work automatically?

In most cases, overboost is automatically activated, usually by accelerating at full throttle. Depending on the make and model of car, the power may actually be limited in the lower gears to avoid wheelspin, with the overboost feature only coming into effect during overtaking manoeuvres or in higher gears.

A few cars, like the performance-oriented Hyundai Veloster N and Elantra N (neither of which is sold here, alas) allow for manual activation of their overboost functions. This provides a small torque boost for up to 20 seconds at a time.

Is overboost useful?

Overboost, used for the purpose of carrying out a quick overtake or to merge safely with fast-flowing motorway traffic is very useful indeed. Minimising the time you spend in these situations can increase your safety on the road.

Seeing as the extra performance is only delivered when necessary, it can also contribute to lower consumption figures.

Can overboost be bad for my engine?

There should be no ill effects to your engine from using overboost as the manufacturer has factored in the extra load during development.

Extra boost over a prolonged period can damage your engine though, but this will only occur if your car’s Electronic Control Unit (ECU) is faulty or has been tampered with. Boosting above the manufacturer’s preset limits can lead to overheating, damaged turbos and broken engine internals.

By only allowing overboost to function for a limited period under specific operating conditions, the extra load put on the engine is minimal. This allows a manufacturer to provide a bit of extra performance without having to develop an engine capable of sustained high boost levels. After all, when did you last need more than 20 seconds of full-bore acceleration in real-word driving?

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