If you’ve spent any time looking at engine descriptions, you’ve probably seen mentions of superchargers and turbochargers. As their names suggest, these components help to boost engine power, and engine power is what helps vehicles, like the Subaru WRX, deliver the performance and speed for which they are known.
Although many car enthusiasts may be familiar with these devices, not everyone is familiar with the differences between them or the details of how they work. With a little reading, however, you can learn how they work, how they differ and how their inclusion can affect your car’s performance.
What are Superchargers and Turbochargers?
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Superchargers and turbochargers are both forced induction systems, which means that they compress the air flowing into the engine. This denser air allows the engine to pack more air and fuel into each cylinder, which in turn makes each combustion event more powerful.
The presence of a supercharger or turbocharger therefore makes an engine more powerful than an otherwise identical engine without these systems. On average, these systems feed 50 percent more air to the engine; in a world without the laws of thermodynamics, this would translate into a 50 percent increase in power, but real-world performance gains are between 30 and 40 percent.
What’s the Difference Between a Supercharger and a Turbocharger?
Functionally, the two devices are fairly similar; the key difference lies in the power supply used to compress the air. Superchargers are connected directly to the engine by a belt, using some of the engine’s energy to power themselves. Turbochargers use a turbine installed in the exhaust system of your vehicle to capture the waste energy of the engine in order to compress the air.
How Does a Supercharger Work?
A Lysholm supercharger. Image courtesy of lysholm.us.
Before understanding how a supercharger works, you need to know how an engine provides power and why a supercharger is necessary to extract more power. It might be tempting to think that you can simply add more fuel to the cylinder to increase performance, but it’s not quite that straightforward. Combustion requires a precise mixture of fuel and air for optimum performance; specifically, engines require 14 parts of air to each part of fuel. By compressing the air flowing into each cylinder, superchargers allow engines to draw in more fuel during the intake stage of a four-stroke engine, making each explosion more powerful. On average, the addition of a supercharger can increase horsepower by 46 percent and torque by 31 percent.
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To compress the air, the supercharger must spin its compressor more rapidly than the engine; typically, a supercharger will complete between 50,000 and 65,000 rotations each minute. In the process of compressing the air, however, the supercharger heats it up as well. The warmer air is thinner and doesn’t combust as well, so most superchargers are also equipped with an intercooler between the exit valves of the supercharger and the cylinders. The intercooler works just like a radiator, forcing the hot air to pass through a series of cooler pipes. Contact with the pipes reduces the temperature of the incoming air and increases its density, ensuring that the incoming air is the optimum temperature for combustion.
Advantages and Disadvantages of Superchargers
The most obvious advantage of superchargers is shared with turbochargers: They increase the power of the engine, allowing smaller engines to deliver the same power as larger ones. When compared to turbochargers, they offer several unique advantages. Since the supercharger is powered directly from the engine’s crankshaft, superchargers deliver increased power immediately. They also perform better than turbochargers at lower engine speeds. Finally, superchargers are easier to install, an important consideration if you’re shopping for an aftermarket unit.
However, there are some disadvantages to superchargers. First, superchargers are less efficient than turbochargers because they bleed off some of the engine’s energy to power themselves. Superchargers place an additional strain on the engine, forcing manufacturers to use more expensive components to compensate. They’re also expensive to maintain and may require drivers to use more expensive premium-grade fuel.
How does a Turbocharger Work?
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Turbochargers work similarly to superchargers; in fact, their official name is turbo-superchargers. The main difference, as mentioned above, lies in the power source. The turbocharger is bolted to the exhaust manifold; a turbine located in the exhaust flow is connected to the air compressor by a shaft. Like a supercharger, it then feeds the compressed air to the engine after cooling the air through an intercooler.
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Turbochargers spin at even higher speeds than superchargers; it’s not unusual for the turbine to reach over 150,000 rotations per minute. These extreme rotational speeds require the use of a fluid bearing to lubricate the shaft; a thin film of oil is constantly pumped into the shaft as the turbine spins. This also helps to cool the shaft.
Advantages and Disadvantages of Turbochargers
Like superchargers, turbochargers significantly increase the power of an engine without adding substantial weight to the vehicle. Turbochargers operate more efficiently than superchargers since they operate primarily on the waste energy of the engine. They can therefore offer more power and better fuel efficiency than superchargers, and they’re easier to maintain.
However, because they’re powered by your engine exhaust, there is often a delay before the boost from your turbocharger reaches your engine. They’re not as effective at lower engine speeds for the same reason. In addition, the presence of a turbocharger puts back pressure on your exhaust system, forcing your cylinders to work harder. The installation of a wastegate and a second, smaller turbocharger can alleviate some of these disadvantages, but doing so increases both the cost and complexity of your turbocharger system.
Engine Knock
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One common drawback to both types of chargers is an increased likelihood of engine knock. The use of compressed air can alter the characteristics of the air-fuel mixture that enters your engine; this new mixture may spontaneously combust when compressed by the piston. Often, this combustion occurs before the spark plug fires, disrupting the normal timing of your engine. The effects of engine knock can range from benign to catastrophic. To combat engine knock, engines with turbochargers or superchargers often require high-octane fuel, which is more resistant to compression-caused combustion.
Which Is Better?
Turbochargers tend to be more efficient and deliver better performance at high engine speeds, but the power boost from a turbocharger doesn’t kick in immediately. Additionally, turbochargers are more complex to install. Superchargers deliver better low-end power, but they’re not as efficient and are more expensive than turbochargers. On the other hand, superchargers are easier to install.
An engine with both a turbocharger and a supercharger. Image courtesy of popularmechanics.com.
Some cars actually include both a supercharger and a turbocharger. An electronic controller switches between the two different systems, using the supercharger for an initial power boost and transitioning to the turbocharger once it’s reached its optimum operating speed. Ultimately, both superchargers and turbochargers are effective at boosting the power output of your engine; the right device for you depends entirely on what you want from your engine.
Which of these two engine-boosting technologies appeals most to you?
Does your car use either of these devices to boost its output?