Superchargers vs. Turbos

What is the difference between a Turbocharger and a Supercharger? It may seem that the two terms are used interchangeably. However, if so, it would be in error. While they both augment an engine’s power, their components are completely different. Essentially, when considering superchargers vs turbos, you are looking at the price and complexity of the part.

What is a Supercharger?

A supercharger is a part of an automobile which works to increase the air density or pressure supplied to the internal combustion engine of the vehicle. This air compressor offers increased power to the engine by giving more oxygen to it in each intake cycle. Therefore, a supercharger enables the engine to do more work and burn more fuel.

Superchargers can be categorized into two main types: dynamic compressors and positive displacement. Dynamic compressors deliver pressure at high speeds, usually above a threshold speed. Positive displacement compressors and blowers deliver pressure increase at a constant level at all engine speeds.

What is a Turbocharger?

When a turbine provides power for the supercharger, the supercharger is referred to as a turbo or turbocharger. The exhaust gas powers these turbine-driven units. They force air into the combustion chamber to increase power and efficiency of the internal combustion engine. Due to forcing extra air, the engine adds more fuel proportionally into the combustion chamber. This further leads to improved output results of the engine.

How Superchargers and Turbochargers Work

The amount of boost produced by a supercharger depends on the impeller rotational speed and size, and the type of compressor. The maximum operating speed of an automotive supercharger is usually over 30,000 RPM while that of a turbo is over 100,000 RPM. Until the impeller reaches the point of maximum speed, the compressor doesn’t produce its full boost.

Turbochargers use centrifugal compressors. They boast the same limitations as a supercharger. In a turbo, the speed of the impeller depends on the speed of the exhaust stream and not on the engine’s speed. The turbine’s speed is not fixed; it changes with the position of the throttle.

The turbine spins below its boost threshold at steady cruising speed. When pressing the gas pedal, there is an increase in speed of the exhaust gasses. This results in the acceleration of the turbine. It takes a bit of time for the turbine to overcome its own inertia and to reach the peak speed. This produces a brief delay, which is termed turbo lag.

Turbo Lag

The amount of boost produced affects the severity of turbo lag. A number of efforts have been made to reduce turbo lag. The list includes reducing the turbine mass, changing their shape, adding movable nozzles, and others.

Some cars use two or more different sized sequential turbochargers, where the smaller turbo responds with good low-speed, and the bigger one provides a maximum boost at peak speeds. A few vehicles such as the 1986-1988 Porsche 959 as well as the 2007 Peugeot 407 2.2 HDi use sequential turbochargers.

It is easier to reduce turbo lag with a turbo featuring low maximum boost. The turbo with light pressure used by some Volvo and Saab engines doesn’t produce good boost, but they have a fairly linear power curve and minimal lag.

Two-stage turbo-superchargers are an even more complex alternative. They use both a turbocharger and an engine-driven supercharger in sequence. This kind of supercharger produces maximum boost even at low speeds. Volkswagen uses this concept with its twincharger engines.

Key Differences between the Turbo and Supercharger

  1. Efficiency
  2. Space Requirement
  3. Mode of Driving Power
  4. Complexity and Cost

Now that you understand how a turbocharger and supercharger work, let’s take a moment to explore the key differences between them.

Efficiency

Turbos tend to be less responsive, but more efficient in comparison to the superchargers. Superchargers consume some amount of engine power even when they are not producing useful boost. The back pressure increased by the turbochargers in the exhaust also costs power. In the case of a turbo, the compressor, even at low speeds, can create some amount of internal drag. The increased power that’s provided by the compressor at maximum boost outweighs these parasitic losses, but the fact can’t be ignored that these losses affect the efficiency of the engine.

Space Requirement

Both turbo and superchargers consume more space in the engine compartment and increase the weight of the vehicle. Typically, the bolt-on superchargers fit easily under the hood, and they weigh less in comparison to the weight of Turbo.

Mode of Driving Power

The engine drives a supercharger which connects through a belt to the crankshaft. A turbocharger’s turbine gets its power from the exhaust gas of the engine.

Complexity and Cost

In order to assure engine efficiency, the moving parts need to be strong and precisely machined. Turbos are made from exotic materials so they can withstand high temperatures and high operating speed of the exhaust system. Forced-induction engines demand proper lubrication, as they tend to put a high strain on the oil system of the engine. It is important to use good-quality oil to ensure best results. Additionally, frequent oil change is also important in superchargers in order to eliminate the possibilities of sludge build-up.

The best application for superchargers and turbos depends on the type of vehicle you outfit. You will find that the turbochargers are most commonly used in Europe because of the smaller engines in European cars. Overall, superchargers deliver better boost at lower RPMs, and they’re comparatively more reliable. Whichever you choose, you can count on boosted performance for your car.

 

References

http://ateupwithmotor.com/terms-technology-definitions/turbocharging-and-supercharging/

http://auto.howstuffworks.com/question122.htm

http://procarmechanics.com/differences-between-superchargers-and-turbochargers/

http://www.carblogindia.com/what-is-a-turbocharger-what-is-a-supercharger-difference-between-turbocharger-and-supercharger/

http://www.redline360.com/garage/supercharger-vs-turbo-which-is-better-and-whats-the-difference

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