Twin-turbo
Encyclopedia
Twin-turbo refers to a turbocharged
engine
, in which two turbochargers compress the intake charge. There are two commonly used twin turbo configurations: parallel twin-turbo and sequential twin-turbo. A third kind of twin-turbocharging, staged turbocharging, is used in diesel
automobile
racing applications.
s. Usually each turbocharger is mounted to its own individual exhaust/turbo manifold, but on inline-type engines both turbochargers can be mounted to a single turbo manifold. Parallel twin turbos applied to V-shaped engines are usually mounted with one turbo assigned to each cylinder bank, providing packaging symmetry and simplifying plumbing over a single turbo setup. When used on inline engines parallel twin turbos are commonly applied with two smaller turbos, which can provide similar performance with less turbo lag than a single larger turbo. Some examples of parallel twin-turbo inline engines are Nissan's RB26DETT, BMW's N54
and Volvo
's B6284T and B6294T. Some examples of V formation engines with parallel twin-turbos include Mitsubishi's 6A12TT and 6G72TT; Nissan's VG30DETT and VR38DETT
; and Audi
's 1997-2002 S4 (B5), 1997-2005 A6
, and 2003-2004 RS6
.
While a parallel twin-turbo set-up theoretically has less turbo lag than a single turbocharger set up, this is not always the case due to many factors. Marginally reduced combined inertial resistance, simplified exhaust plumbing, and the simultaneous spooling of both turbos means that there can still be a noticeable bit of lag, especially in high-flow turbo/high boost applications. Some ways to counter this are to use a light pressure set up with smaller turbos, where the turbos are designed to output less boost but spool earlier. While this setup sacrifices some top end power, it still has less lag than a similar engine with a single turbo set up making the same power. Another system would be the use of variable geometry turbocharger
s. This system changes the angle of the guide vanes depending on the exhaust pressure, giving the system excellent power throughout the rev range. Once used mainly in turbocharged diesel engine
s, Chrysler was the first to use it in mass-production gasoline-powered vehicles with the Shelby CSX
, debuted in 1989.
It is possible to use parallel operation with more than two turbochargers. Two such examples are the Bugatti EB110
and Bugatti Veyron
, both of which run four turbochargers in parallel. The EB110 runs 4 turbos on a 3.5 litre V12 engine, producing 542 hp (404 kW) at 8000 rpm, while the Veyron uses a 16 cylinder engine to generate 1200 PS.
Sequential turbocharger systems provide a way to decrease turbo lag without compromising ultimate boost output and engine power. Examples of cars with a sequential twin-turbo setup include the 1986-1988 Porsche 959
, the 1990-1995 Eunos Cosmo JC, 1992-2002 Mazda RX-7 Turbo (FD3S), the 1993-1998 Toyota Supra Turbo (JZA8x), the 1994-2005 JDM Subaru Legacy GT, GT-B & B4 RSK
, and the 2008-2010 Ford Super Duty 6.4L diesel.
engines.
ACERT engines utilize sequential turbos as well as International
on some of their newest engines.
Turbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
, in which two turbochargers compress the intake charge. There are two commonly used twin turbo configurations: parallel twin-turbo and sequential twin-turbo. A third kind of twin-turbocharging, staged turbocharging, is used in diesel
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
automobile
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
racing applications.
Parallel twin-turbo
Parallel twin-turbo refers to a turbocharger configuration in which two identical turbochargers function simultaneously, splitting the turbocharging duties equally. Each turbocharger is driven by half of the engine's spent exhaust energy. In most applications, the compressed air from both turbos is combined in a common intake manifold and sent to the individual cylinderCylinder (engine)
A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...
s. Usually each turbocharger is mounted to its own individual exhaust/turbo manifold, but on inline-type engines both turbochargers can be mounted to a single turbo manifold. Parallel twin turbos applied to V-shaped engines are usually mounted with one turbo assigned to each cylinder bank, providing packaging symmetry and simplifying plumbing over a single turbo setup. When used on inline engines parallel twin turbos are commonly applied with two smaller turbos, which can provide similar performance with less turbo lag than a single larger turbo. Some examples of parallel twin-turbo inline engines are Nissan's RB26DETT, BMW's N54
BMW N54
The N54 is a direct injection twin-turbocharged straight-6 automobile engine from BMW. It was launched in late 2006 as a high-performance option for the BMW 3-Series, first to be released along with the new 3-series E92 Coupé, to be followed closely by other existing 3-series models, then with...
and Volvo
Volvo
AB Volvo is a Swedish builder of commercial vehicles, including trucks, buses and construction equipment. Volvo also supplies marine and industrial drive systems, aerospace components and financial services...
's B6284T and B6294T. Some examples of V formation engines with parallel twin-turbos include Mitsubishi's 6A12TT and 6G72TT; Nissan's VG30DETT and VR38DETT
Nissan VR engine
The VR engine is a 3.8 L V6 piston engine from Nissan. The engine is the product of further development of the widely successful VQ engine series, in particular drawing experience from the JGTC racing engines as well as Nissan's VRH engines from vehicles such as the Nissan R390...
; and Audi
Audi
Audi AG is a German automobile manufacturer, from supermini to crossover SUVs in various body styles and price ranges that are marketed under the Audi brand , positioned as the premium brand within the Volkswagen Group....
's 1997-2002 S4 (B5), 1997-2005 A6
Audi A6
The Audi A6 is an executive car marketed by the German automaker Audi AG, now in its fourth generation. As the successor to the Audi 100, the A6 is manufactured in Neckarsulm, Germany – and is available in saloon, and wagon configurations, the latter marketed by Audi as the Avant.All generations...
, and 2003-2004 RS6
Audi RS6
The Audi RS6 quattro, commonly referred to as the RS6, is the highest performing version, and top-of-the-line specification of the Audi A6, positioned above the Audi S6...
.
While a parallel twin-turbo set-up theoretically has less turbo lag than a single turbocharger set up, this is not always the case due to many factors. Marginally reduced combined inertial resistance, simplified exhaust plumbing, and the simultaneous spooling of both turbos means that there can still be a noticeable bit of lag, especially in high-flow turbo/high boost applications. Some ways to counter this are to use a light pressure set up with smaller turbos, where the turbos are designed to output less boost but spool earlier. While this setup sacrifices some top end power, it still has less lag than a similar engine with a single turbo set up making the same power. Another system would be the use of variable geometry turbocharger
Variable geometry turbocharger
Variable-geometry turbochargers are a family of turbochargers, usually designed to allow the effective aspect ratio of the turbo to be altered as conditions change. This is done because optimum aspect ratio at low engine speeds is very different from that at high engine speeds...
s. This system changes the angle of the guide vanes depending on the exhaust pressure, giving the system excellent power throughout the rev range. Once used mainly in turbocharged diesel engine
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
s, Chrysler was the first to use it in mass-production gasoline-powered vehicles with the Shelby CSX
Shelby CSX
The Shelby CSX was a limited-production high performance automobile based on the turbocharged Dodge Shadow. These cars were offered by Shelby Automobiles Inc. from 1987 through 1989.-CSX:...
, debuted in 1989.
It is possible to use parallel operation with more than two turbochargers. Two such examples are the Bugatti EB110
Bugatti EB110
The Bugatti EB110 is a mid-engine sports car from Bugatti Automobili SpA. It was unveiled on September 15, 1991, in both Versailles and in front of the Grande Arche at La Défense in Paris, France, exactly 110 years after Ettore Bugatti's birth....
and Bugatti Veyron
Bugatti Veyron
The Bugatti Veyron EB 16.4 is a mid-engined grand touring car. The Super Sport version is the fastest road-legal production car in the world, with a top speed of . The original version has a top speed of...
, both of which run four turbochargers in parallel. The EB110 runs 4 turbos on a 3.5 litre V12 engine, producing 542 hp (404 kW) at 8000 rpm, while the Veyron uses a 16 cylinder engine to generate 1200 PS.
Sequential turbos
Sequential turbos refer to a set-up in which the motor utilizes one turbocharger for lower engine speeds, and a second or both turbochargers at higher engine speeds. Typically, larger high-flow turbochargers are not as efficient at low RPMs, resulting in lower intake manifold pressures under these conditions. On the other hand, smaller turbos spool up quickly at low RPMs but cannot supply enough air at higher RPMs. During low to mid engine speeds, when available spent exhaust energy is minimal, only one relatively small turbocharger (called the primary turbocharger) is active. During this period, all of the engine's exhaust energy is directed to the primary turbocharger only, providing the small turbo's benefits of a lower boost threshold, minimal turbo lag, and increased power output at low engine speeds. As RPM increases, the secondary turbocharger is partially activated in order to pre-spool prior to its full utilization. Once a preset engine speed or boost pressure is attained, valves controlling compressor and turbine flow through the secondary turbocharger are opened completely. (The primary turbocharger is deactivated at this point in some applications.) In this way a full twin-turbocharger setup provides the benefits associated with a large turbo, including maximum power output, without the disadvantage of increased turbo lag.Sequential turbocharger systems provide a way to decrease turbo lag without compromising ultimate boost output and engine power. Examples of cars with a sequential twin-turbo setup include the 1986-1988 Porsche 959
Porsche 959
The Porsche 959 is a sports car manufactured by Porsche from 1986 to 1989, first as a Group B rally car and later as a legal production car designed to satisfy FIA homologation regulations requiring that a minimum number of 200 street legal units be built....
, the 1990-1995 Eunos Cosmo JC, 1992-2002 Mazda RX-7 Turbo (FD3S), the 1993-1998 Toyota Supra Turbo (JZA8x), the 1994-2005 JDM Subaru Legacy GT, GT-B & B4 RSK
Subaru Legacy
The Subaru Legacy is a mid-size car built by the Japanese company Fuji Heavy Industries, and manufactured by its division Subaru since 1989, and is available as a sedan or wagon. Part of the original design goals for the Legacy model was to provide Subaru a vehicle in which they could compete in...
, and the 2008-2010 Ford Super Duty 6.4L diesel.
Staged turbos
A sequential turbo can also refer to a system where the output pressure must be greater than can be provided by a single turbo, commonly called a staged twin turbo system. In this case, multiple similarly sized turbochargers are used in sequence, but both operate constantly. The first turbo boosts pressure as much as possible (for example to three times the intake pressure). Subsequent turbos takes the charge from the previous stage and compresses it further (for example to an additional three times intake pressure, for a total boost of nine times atmospheric pressure). This configuration is commonly found on piston engine aircraft which usually do not need to rapidly raise and lower engine speed (and thus where turbo lag is not a primary design consideration), and where the intake pressure is quite low due to low atmospheric pressure at altitude, requiring a very high pressure ratio. High-performance diesel engines also sometimes use this configuration, since diesel engines do not suffer from pre-ignition issues and can use significantly higher boost pressure than Otto cycleOtto cycle
An Otto cycle is an idealized thermodynamic cycle which describes the functioning of a typical reciprocating piston engine, the thermodynamic cycle most commonly found in automobile engines....
engines.
Advantages in Diesel emissions
While spark ignition engines have fallen out of favor of the sequential turbo design, many diesel companies now make engines with sequential turbos in order to reduce emissions. Caterpillar Inc.Caterpillar Inc.
Caterpillar Inc. , also known as "CAT", designs, manufactures, markets and sells machinery and engines and sells financial products and insurance to customers via a worldwide dealer network. Caterpillar is the world's largest manufacturer of construction and mining equipment, diesel and natural gas...
ACERT engines utilize sequential turbos as well as International
International Harvester
International Harvester Company was a United States agricultural machinery, construction equipment, vehicle, commercial truck, and household and commercial products manufacturer. In 1902, J.P...
on some of their newest engines.
See also
- Boost gaugeBoost gaugeA boost gauge is a pressure gauge that indicates manifold air pressure or turbocharger or supercharger boost pressure in an internal combustion engine...
- Boost controllerBoost controllerA boost controller is a device to control the boost level produced in the intake manifold of a turbocharged or supercharged engine by affecting the air pressure delivered to the pneumatic and mechanical wastegate actuator...
- SuperchargerSuperchargerA supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
- IntercoolerIntercoolerAn intercooler , or charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged internal combustion engines to improve their volumetric efficiency by increasing intake air charge density through nearly isobaric cooling, which removes...
- TwinchargerTwinchargerTwincharger refers to a compound forced induction system used on some piston-type internal combustion engines. It is a combination of an exhaust-driven turbocharger and an engine-driven supercharger, each mitigating the weaknesses of the other...