In this blog post, we’ll examine the relationship between a car’s displacement and engine performance, explore the principles, advantages, and disadvantages of turbochargers—which enable even small-displacement engines to deliver strong power and output—and look at how turbocharged engines are being utilized in the automotive industry today.
In 2012, Hyundai Motor Company launched the “Veloster Turbo,” a high-performance model. To emphasize that it was a completely different car from previous models, Hyundai featured the Veloster Turbo racing against a cheetah in its advertisement to showcase its increased power and speed. In the end, the cheetah in the commercial gives up shortly after the race begins. How different is this 1,600cc-class engine—the same as that in the standard Veloster—that Hyundai felt confident enough to create such a bold advertisement? The answer lies in the two letters: “Turbo.” Anyone with even a passing interest in cars will likely recall seeing the word “Turbo” used in the model names or engine designations of certain vehicles. “Turbo” is short for “turbocharger.” A turbo engine generally refers to an internal combustion engine equipped with a turbocharger; compared to a naturally aspirated engine of the same displacement, it delivers more air to the cylinders, resulting in higher power and torque. In fact, when Hyundai Motor Company launched the Veloster Turbo in 2012 with a 1.6-liter turbo engine, it was an example of utilizing these characteristics of the turbocharger.
So why are turbo engines more powerful? To understand the reason, we need to grasp the basic operating principles of a car engine. Just as humans eat food to obtain energy, cars burn fuel to generate the energy needed to move. Fuel combustion is the process by which fuel reacts with oxygen, and generally, burning more fuel requires a sufficient amount of air to support it. When fuel and air combust inside the cylinder, high temperatures and pressure are generated, and this pressure pushes the piston outward. The piston’s reciprocating motion is converted into rotational motion via the connecting rod and crankshaft, which is ultimately transmitted as the power that drives the car. In other words, when a car produces greater power, it means the engine can generate greater torque, and when it produces higher output, it means it can perform more work within a given time. Therefore, one way to increase a car’s power and output is to burn more fuel in the same amount of time. To do this, more air must be supplied to the engine to ensure the fuel burns completely; however, in naturally aspirated engines, the amount of air that can be supplied to the cylinders is significantly limited by the engine’s design and displacement. Displacement is the total volume swept by the pistons as they move within each cylinder of the engine—that is, the sum of the stroke volumes—and is commonly used to indicate the engine’s size in cc. Generally, a larger displacement allows for the combustion of more air and fuel, which is advantageous for achieving higher output; however, it also increases the likelihood of the engine becoming larger and heavier.
However, since increasing displacement involves increasing the engine’s physical size and weight, there are inherent limits. Therefore, methods are used to supply more air to the engine without significantly increasing displacement, and a prime example of such a device is the turbocharger. When a gas is compressed, more mass can be packed into the same space, thereby increasing the density of the air supplied to the engine. This allows for the injection and combustion of a corresponding amount of additional fuel, resulting in greater power output. The method of compressing air to deliver more of it into the cylinders—rather than increasing displacement—can be likened to packing rice tightly into a person’s stomach to eat more, rather than enlarging the stomach itself. A turbocharger consists primarily of a turbine, which rotates using the energy from exhaust gases, and a compressor, which compresses the intake air; these two components are connected by a single shaft and rotate together. When exhaust gases from the engine pass through the turbine after combustion, they cause the turbine to spin rapidly, and this rotational force is transmitted to the compressor via the shaft. The compressor draws in outside air, compresses it, and sends it to the engine; the compressed air can be supplied to the cylinders at a higher density than in naturally aspirated engines. Since more air can be supplied to the cylinders in this way, a corresponding amount of fuel can be burned, resulting in high power and torque even with a small displacement. Ultimately, the reason turbo engines are described as “powerful for their size” is that they can increase the mass of air supplied to the cylinders using a turbocharger without significantly increasing the engine’s physical size or displacement.
These turbo engines offer several advantages. First, they can be used in the development of high-performance vehicles, making it easier to achieve high power and torque even with small-displacement engines. Furthermore, they can be utilized in downsizing strategies, where a turbocharger is applied to an engine with a reduced displacement to maintain performance comparable to conventional engines while reducing engine size and friction losses. However, just because an engine is turbocharged does not necessarily mean it offers better fuel economy; actual fuel consumption is influenced by various factors, including engine design, vehicle weight, driving conditions, and driving style. Another drawback of turbocharged engines is turbo lag. Conventional turbochargers rely on the force of exhaust gases to spin the turbine, so it may take a certain amount of time for sufficient boost pressure to build up immediately after the driver presses the accelerator pedal. As a result, the driver may experience a slight delay or a sense of disconnection during acceleration. However, recent advancements—such as variable-geometry turbochargers, multi-stage turbochargers, and electric boost systems—are being used to reduce turbo lag and improve responsiveness. In particular, systems that use electric motors to assist the turbocharger or supercharger are being employed to improve responsiveness and reduce turbo lag by rapidly supplying air even at low engine speeds. Furthermore, since turbochargers operate in high-temperature, high-pressure environments, they require a high level of design and manufacturing expertise; this technical complexity can lead to increased development and manufacturing costs for engines and vehicles.
So far, we have examined why turbocharged engines are more powerful than naturally aspirated engines of the same displacement. To improve engine performance, more air and fuel must be combusted efficiently; the primary methods for achieving this are increasing displacement or compressing air to supply a greater volume to the cylinders. Turbocharged engines utilize the energy from exhaust gases to compress air and supply a greater volume of air to the cylinders, thereby producing higher power and torque relative to the engine’s displacement. Advantages include their applicability in the development of high-performance vehicles and their use in “downsizing”—reducing displacement while maintaining performance—while disadvantages include turbo lag, high technical complexity, and the resulting increase in costs. In the past, these drawbacks were cited as significant limitations of turbocharged engines; however, as turbocharger technology has advanced, various technologies are being applied to improve responsiveness and efficiency. Furthermore, in the automotive industry today, there are growing instances where turbochargers and electric boost technologies are used in conjunction not only in pure internal combustion engines but also in electrified powertrains such as hybrids and plug-in hybrids. Data from the U.S. Department of Energy also shows that 37% of light-duty vehicles produced in 2023 were equipped with turbochargers, demonstrating that turbochargers remain a key technology for miniaturization and power enhancement. However, since electric vehicles lack an internal combustion engine, they do not require turbochargers. Rather than simply moving toward a future where turbocharged engines replace all existing engines, the automotive industry is likely to evolve in a direction where the efficiency and responsiveness of turbochargers in internal combustion engines and hybrid powertrains are further enhanced, while new power sources, such as electric vehicles, continue to expand.
