What is the difference between a turbocharger and a supercharger?
Turbochargers and superchargers are both forced induction systems. Both compress the intake air and pump more oxygen into the cylinders. Both benefit from additional charging of the combustion chambers as it increases the maximum torque and the engine output. So both can see a significant power boost – up to 50% more – from a relatively small engine capacity. But what about the differences? The best way to describe these is to first cover how everything works…
What is a turbocharger and how does it work?
The first thing to know is that a turbo is, quite simply, an air pump. It allows more air to be pumped into the engine at high pressures, mimicking the effect of a larger cylinder. More air allows more fuel flow, which is how more power is achieved. The next thing to know is that a turbo is made up of two sections – compressor and turbine – and the process works as follows:
The turbo is mounted on the engine exhaust manifold and fed with exhaust gases. Once the exhaust gases are expelled through the exhaust port, the gases pass through the exhaust manifold and are fed to the turbine housing of the turbocharger.
The compressor wheel (on the inlet side) and the turbine wheel (on the exhaust side) are connected to each other. The efficiency of the turbo system is higher than that of the compressor because, while the compressor is mechanically coupled to the engine and uses its drive power to compress the fresh air, the turbocharger works largely without loss of energy. This means that the turbocharger can use the pressure and energy of the hot exhaust gas flow for charging, while the compressor achieves a lower overall efficiency through a mechanical connection to the crankshaft.
When the exhaust gases come out of the exhaust manifold, the gases can go in two directions: either the exhaust gases go through the wastegate if it is open, or they go through the exhaust turbine when the wastegate is closed. The exhaust turbine, in turn, starts drawing in air through the air filters. As the compressor wheel turns, it sucks in and compresses air before sending the air to the inlet.
Once this combustion process starts, it creates a continuous cycle, and the spin speed is very impressive – a standard turbine wheel can achieve up to 200,000 rpm!
Important things to know about turbos
Given the spin speed, the main shaft must have a good oil supply to prevent wear. In addition, the axle and wheels must be very well balanced as with such a fast-spinning turbo, every small vibration might cause the turbo to destroy itself in a few seconds.
A disadvantage of the turbo is that it actually limits the engine power. Since the turbocharger is part of the exhaust system and the exhaust gases are forced to flow through it, it actually causes a restriction on the exhaust itself as well. This is why the exhausts can quickly become very hot with a turbo, and you can even see them light up in the dark. Ultimately, they waste a lot of energy on heat.
What is a supercharger and how does it work?
In principle, the supercharger is very similar to the turbocharger. A supercharger also pushes air to the engine, but the big difference is that exhaust gases do not power it. Instead, a supercharger is belt-driven from the engine. This means that the engine's speed determines the supercharger's speed, so it does not require a wastegate or a boost pressure regulator. Additionally, to create a bigger boost, you can make the supercharger work harder from within the software. Or, if it is running at maximum, there is also the option of changing the pulley.
Situated at the end of the input shaft, the supercharger pulley size is directionally proportionate to the speed that the supercharger turns. If you alter the size of the pulley, you change the drive ratio – and get more boost.
There are three types of supercharger:
Roots-type
Centrifugal
Twin-screw
The main difference between these superchargers is in the kind of compressor used. The roots-type supercharger is often called an external compression pump because there is no air compression in the 'charger' itself. Centrifugal and twin-screw superchargers, however, are considered internal compression superchargers because the rotors in these systems compress the air in the unit itself, and then send this compressed air to the engine's intake manifold.
The pros and cons of a supercharger
The supercharger has a significant advantage over a turbo in that the exhaust system does not need to be adjusted. This is why naturally aspirated engines are more often converted with a supercharger, as this is a lot simpler and cheaper. In addition, superchargers are generally more efficient, so in general, smaller intercoolers can be used, or none at all.
As with everything in life, there's always a downside. And here, it's that it can take 100 horsepower just to propel the supercharger. Also, the size of the supercharger can be an issue – as Drag Race fans will know, some superchargers won't even fit under the bonnet. Excellent for show cars, but not very practical for your weekday commute.
Two technologies with one goal: more performance
In these challenging times, when global fuel prices are rapidly rising, especially for diesel vehicles, cars are in the media every day. And although the environment is also a concern for many, the demand for high-performance cars remains high. Ultimately, when considering the difference between turbochargers and superchargers – and which you personally prefer in your ride – there are a couple more things to consider:
After-lag
Each of these performance-enhancing technologies has its pros and cons. For example, modern turbochargers reach speeds of almost 300,000 rpm, and the plain bearings of the turbocharger shaft are very sensitive.
However, the most obvious difference for the driver of a turbocharged vehicle compared to a supercharged model is the slight lag in response, especially when the accelerator pedal is fully depressed. That's because the turbocharger needs a moment to rev up before there's an extra boost, as it takes a short time until the waste heat and the pressure are sufficiently high.
In contrast, a supercharger has no delay. Since the pump is connected directly to the engine's crankshaft, it continuously rotates and reacts immediately. Therefore, the increase in performance occurs as soon as you press the accelerator pedal.
Fuel consumption
The power that an internal combustion engine can produce depends on how much fuel it can burn and how quickly and efficiently that heat is converted into mechanical power. However, energy requires air (actually the oxygen contained in the air) to burn. Therefore, an engine's maximum power depends mainly on how much air it can take in to burn the fuel.
So while the main disadvantage of the turbo is the after-lag, it is the efficiency with the supercharger that should be considered. Because a supercharger uses the engine's own power to spin itself, it siphons off the power. Such engines, therefore, tend to consume more fuel.
The (current) automakers' choice
The automakers have a clear favourite right now: the turbocharger wins because of its fuel efficiency. However, politics is the driving factor here, as the requirements for more environmentally friendly vehicles are becoming ever more stringent.
Turbos make it possible to replace V6 engines with four-cylinder ones, which offer more torque for the same power. The same applies to V8 vs V6 aggregates. However, only a few brands, such as Volvo, use both technologies in their models.
So what if the problem of fuel consumption and lag could both be solved with something new...?
Electric charging as a future-oriented alternative
A third variant is now on the market, which is likely to shake things up considerably: electric charging. V6 turbochargers are combined with an electrically driven compressor to plug the well-known turbo lag to create a torque burst. So while the turbocharger is currently still in the lead, the supercharger is far from dead.
Although car manufacturers may appear to have chosen turbocharging for virtually all of their current power-boosted engines, the truth is that this battle between the rival technologies is likely to continue. In fact, it seems probable that the future of internal combustion engines could involve both technologies working together.
