What is a turbo?

  • How do turbos work and how much difference do they make?
  • Why is forced-induction so common nowadays?
  • Parkers provides the ultimate turbo guide

Originally the preserve of high-performance cars, turbos use recirculated exhaust gases to improve efficiency and produce more power from the engine. 

Why have turbos become more popular?

Before the recent rise in turbocharging popularity, if a car manufacturer wanted its models to go faster the normal practise was to install a larger, more powerful engine. While this made the car go quicker, it wasn’t the most efficient way of achieving speed – the extra weight and size of the engine guzzled more fuel in the process.

Turbocharging as a means of increasing performance started in a small way in the 1960s in North America (Oldsmobile Jetfire) and the 1970s in Europe (Porsche 911 Turbo), steadily becoming more commonplace over the next two decades.

It was during the late 1990s and early 2000s that turbocharging as a means of delivering performance and  efficiency became more widespread. Larger engines were gradually replaced in car manufacturers’ line-ups with smaller, turbocharged engines – today’s Ford Mondeo can be bought with a three-cylinder, 1.0-litre turbo engine, for instance.

The benefits these small turbocharged powerplants offer are higher levels of fuel efficiency and lower CO2 emissions without sacrificing the speed buyers have become accustomed to. Reducing CO2 output benefits car buyers in terms of lower VED car tax, and allows car makers to meet ever-tighter exhaust gas legislation.

How do turbos work?

A non-turbo (naturally aspirated) engine sucks air into its cylinders via inlet valves and, post-combustion, releases the resultant gas by opening the exhaust valves.

When a turbo is fitted, a turbine is spun by the passing exhaust gasses, which in turn draws air into the engine’s combustion chamber quicker.

Consequently air is forced back out of the engine, spinning the turbine further still and so the cycle continues, increasing both power and efficiency as it does so, giving off a characteristic high-pitched whirring sound as it spins.

The time taken for the exhaust gas to start rotating the turbine is known as turbo lag. Older turbocharged cars used to suffer this terribly with power coming on like a switch had been flicked, but modern units aren’t blighted to such a degree, with a more progressive delivery.

A small number of cars are fitted with two turbos (known as twin-turbos or bi-turbos), while fewer still have ever used more than that – think supercars and similar exotica.

Other variations include variable-geometry turbochargers, where two sets of internal vanes on the turbine are designed to work in such a way as to boost power at lower engine speeds and efficiency at higher ones.

A more recent development – lead by Audi and Volvo, the latter with its PowerPulse device – shoot bursts of compressed air straight into the turbine at low speeds, virtually eliminating turbo lag in the process.

Superchargers – sometimes known as compressors, or Kompressors in Mercedes-speak – are mechanical devices connected to the engine via a belt to force air into the combustion chamber. They have fallen out of favour to turbos in recent times due to being unable to match the latter’s efficiency levels.

Do I need one?

Yes – all diesel-engined cars sold in the UK have been turbocharged for years and the majority of petrol units similarly feature forced induction.

Forget notions of boy racers and lairy “Turbo” graphics across the bootlids of cars, turbocharging is now so common, most cars that are so equipped don’t bother to advertise the fact – would you know a Fiat’s engine was turbocharged from its MultiAir name?

Today’s turbos not only give you a performance boost, they do so in a way that’s fuel efficient and low-CO2 emitting.

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Almost every new car you can buy!

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Looking for more jargon-busting motoring meanings? Head over to our Parkers Car Glossary page and take a look at our other definitions