Supercharger vs. Turbo

Forced induction

The basic function of both superchargers and turbos is to deliver more air to an engine’s internal combustion process.

Supercharger

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  • 1 Air filter

  • 2 Air intake pipe

  • 3 Intake manifold

    The supercharger sits atop the intake manifold. The intake manifold channels air from the supercharger unit to individual cylinders.

  • 4 Supercharger housing

  • 5 Gear drive system

    Opposing gears translate power to the rotors.

  • 6 Rotor & lobes

    Spinning rotors pump air through the supercharger. The long fins or ridges that span the length of the rotor shaft are called lobes.

  • 7 Discharge port

    Air exits the supercharger through a specially shaped discharge port at the bottom of the housing.

  • 8 Pulley

    Pulley diameter and construction is an easily accessible way to alter supercharger performance characteristics.

  • 9 Drive belt

    The drive belt supplies power to the supercharger from the crankshaft.


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Popular types

  • Roots

    The roots type supercharger saw its first automobile application in 1900. The term “blower” or “blown engine” originates from the roots supercharger’s basic function as an air blower, as opposed to other designs that compress air.

  • Twin screw

    Twin screw type superchargers feature complex rotors with intricately designed lobes that compress air as it moves through the unit. This increased complexity results in better performance, but also higher manufacturing cost.

  • Centrifugal

    Centrifugal type superchargers have much in common with the turbocharger design concept, but are driven by mechanical engine power instead of exhaust gas.

Turbo

  • 1 Exhaust manifold

    A turbo system often requires a specially designed exhaust manifold to handle exhaust heat and pressure, and to properly deliver exhaust gas to the turbo unit.

  • 2 Turbine section

    Engine exhaust flows through the turbine section of the turbo.

  • 3 Exhaust wheel

    Energy from exhaust heat and pressure spins a turbine called the exhaust wheel

  • 4 Shaft

    A shaft connects and supports the exhaust and compressor wheels

  • 5 Compressor section

    Incoming air is pumped through the compressor section of the turbo.

  • 6 Compressor wheel

    The spinning compressor wheel draws air into the compressor chamber and builds compression.

  • 7 Air intake manifold

  • 8 Air intake pipe

  • 9 Air filter

  • 10 Turbo housing & scroll shape

    The turbine and compressor chambers have a spiral shape like a rolled up scroll, though the term “scroll” in connection with turbos often refers to the exhaust chamber (i.e.: twin-scroll).


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Popular types

  • Single turbo

    A single turbocharger setup.

  • Twin turbo

    A setup with two turbochargers, e.g. a 6-cylinder “V” formation engine with a turbo for each cylinder bank.

  • Twin scroll turbo

    Exhaust exits the cylinder in a pulse, with a high pressure section followed by low pressure. Twin scroll turbos separate cylinders into pairs so that exhaust pulse waves do not interfere with each other, and a continuous stream of maximum pressure exhaust reaches the turbine.

Overview

  • Supercharger

  • Turbo

Function

  • Superchargers are powered by mechanical energy; for example, by connection to an engine’s crankshaft.

  • Turbos are powered by otherwise wasted heat energy from engine exhaust.

Boost characteristics

  • Roots and twin screw models have “positive displacement”, meaning that they move the same amount of air for each engine revolution, regardless of RPM. This also means that they can make boost immediately (even at low RPMs), and have a fairly linear power curve.

    Centrifugal models have an exponential power curve, and must build up pressure to make boost. They make little usable boost at low RPMs, and are tuned to make full boost at redline.

  • Basic turbo setups produce an exponential power curve. Since they are powered by exhaust, turbos take time to build turbine speed and pressure (spool up) before producing usable boost. This is what’s known as “turbo lag”.

Efficiency

  • Superchargers take power to make power, and an average setup can require 40-60 horsepower to function. This does not, however, mean that overall engine efficiency is always sacrificed as some setups can increase fuel economy when not driven aggressively.

  • Though turbos do increase back pressure on the engine, they derive power primarily from otherwise wasted exhaust heat as opposed to exhaust flow pressure. As such, they can be very efficient.

Conclusion

  • Superchargers can be a less complex, less expensive way to increase engine performance. They are usually easier to tune and maintain. Superchargers can be ideal in applications that require predictable boost at all RPMs, e.g., drag racing.

  • Turbos often require more peripheral parts like oil and vacuum lines, intercoolers, custom exhaust manifolds and exhaust piping, etc.; and can require more skill to properly configure. However, a well tuned turbo system may be able to produce boost more efficiently and in greater quantity than a supercharger.

References
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