How do turbos work, and how do they differ from superchargers?

Turbocharging makes everything better, right?

Any survivors from the 1980s will remember the term could be loosely applied to anything – turbo razors, turbo sunglasses and turbo skateboards to name but a handful. But what are (real) turbos?

The simplest way to understand them is to consider that an engine needs to mix fuel and air to run. Turbos force more air into the cylinder, which can be mixed with more fuel to create more power. Turbos use the energy of the engine’s exhaust gasses to compress air into the engine.

How do they work?

Turbos are formed of two main parts – a turbine and a compressor. These are linked so, when the one spins, the other spins with it. As fuel in the engine is burnt, exhaust gasses are forced out of the engine at high pressure, down a snail-shaped tube to spin the turbine. This turbine spins at incredibly high speeds (up to 250,000rpm) and causes the compressor (effectively a reversed turbine) to spin. This sucks significantly more air into the engine than a normally-aspirated (non-turbo) unit, making more power.

Turbos run at immense speeds which means they operate under huge pressures and temperatures. Typically, an intercooler is paired with the turbocharger to cool the hot air coming out of it and an oil cooling system ensures the turbo itself doesn’t run too hot. Diesels, having tougher engine blocks and simpler intakes, are ideally suited to being turbocharged so all modern diesels have them.

What are the benefits?

More power is the glaring headline here, but it’s far from the only advantage. Turbo engines can make the same power as a normally-aspirated engine while using less fuel. Hence why Ford, for example, has replaced the old 1.6-litre petrol engine with a new 1.0-litre turbo – it makes the same power but uses much less fuel.

Turbos also give engines more torque – often lower down in the rev range. This means they feel much stronger around town where the extra torque makes nipping into gaps easier. Another, unexpected, advantage is that turbos actually make for a quieter engine as they muffle the sound of the intake.

Any downsides?

Not many, which is why they’re so common in engines now. Mainly, they add cost and complexity to an engine – becoming just another part to go wrong – and, with the high temperatures and pressures they operate at, when they do, it’s often in quite a spectacularly expensive fashion.

There’s another thing. Reviewers often talk of turbo lag – a brief delay between pressing the throttle and the engine making power. This is caused when the exhaust gasses are not at the required pressure to spin the turbine optimally, hence the delay as the turbo comes ‘on boost’. Car makers try to mitigate this by using more smaller turbos instead of one big one, turbos with multiple optimum operating speeds or, for some race cars, a fearsome anti-lag system that causes 10ft flames to shoot out the back of the car!

Careful control of the throttle in a turbo car is required if you want to get close to the claimed efficiency figure – turbos are efficient when cruising ‘off boost’ (ie when the turbo isn’t really working) but very inefficient when ‘on boost’. This means that you may need to alter your driving style if you’re coming from a non-turbo car.

What about superchargers?

Superchargers do the same job as a turbocharger – they force more air into the cylinder to make more power. The difference lies in how each device is powered. Turbos rely on the pressure of exhaust gasses to compress the air, whereas superchargers are mechanically driven by the engine’s crankshaft.

Superchargers boost power and are said to have better throttle response than turbos because the mechanical connection between the supercharger and the engine eliminates the lag. They do, however, cause parasitic power losses by being connected to the engine and therefore can’t match the efficiency of turbos.

Some history…

Superchargers were dreamed up by Gottlieb Daimler in the late 19th century but turbos weren’t patented until 1905. They didn’t become commonplace until the end of World War I, when pilots found they were the ideal way to combat the lower oxygen density at the higher altitudes they were achieving. Turbos improved through aviation, using better materials, built to finer tolerances to create more boost.

The first turbo passenger car was the Oldsmobile Cutlass in the USA which strapped a turbo to its 3.5-litre V8 in 1961 to make 215hp – this engine (without turbo) went on to become the famed Rover V8. Their complexity took them out of market favour until Saab reinvented the tech with its 99 Turbo in 1984 pushing them back where they have stayed ever since. With tighter modern legislation – they’re here to stay.

What models can I get turbos in?

Almost all manufacturers offer a turbocharged model of one sort or another. Volkswagen-group models are badged TSI for turbo-petrols and TDI for turbodiesels. Ford’s are called Ecoboost for petrol and TDCI for diesel. Renault-Nissan alliance vehicles are badged TCi and diesels are dCi. To name a few.