Supercharger vs Turbo

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

Air filter

Air intake pipe

Intake manifold

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

Supercharger housing

Gear drive system

Opposing gears translate power to the rotors.

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.

Pulley

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

Drive belt

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

Various supercharger 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 superchargers, though mechanically driven instead of exhaust powered, have much in common with the turbo design concept. They produce an exponential power curve and are often tuned to make full boost at redline.

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.

Turbine section & exhaust wheel

Exhaust flows through the turbine section; exhaust heat and pressure drive a turbine called the exhaust wheel.

Shaft

A shaft connects and supports the exhaust and compressor wheels

Compressor section & wheel

Incoming air is pumped through the compressor section, building compression as the compressor wheel spins.

Air intake manifold

Air intake pipe

Air filter

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).

Various turbo 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.

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.

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. Supercharges 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.

Superchargers are mechanically driven while turbos are powered by exhaust gas.

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References