Twin turbo

Engine of a Porsche 935 six-cylinder plane with a double turbocharger

A biturbo engine (or twin turbo, as it is also called in English) is an internal combustion engine that has two turbochargers. The most common arrangement carries both turbos identically in parallel; It can also have a sequential or staged turbo arrangement, the latter used in diesel competition vehicles.

Twin turbo in parallel

Ford EcoBoost 3.5 engine (biturbo)

Parallel twin-turbo engines consist of a configuration in which both turbos simultaneously operate in an identical fashion, sharing an equal turbo intake. Each of them is driven by one half of the engine. In most cases, the compressed air from both turbos is combined into a single intake manifold and delivered to the cylinders individually. Generally, each turbo is fitted with its own intake and exhaust manifold, but twin-turbo inline engines may have a single turbo inlet manifold. Parallel biturbos applied to V-shaped engines usually mount a turbo for each bank of cylinders, providing less volume and more symmetry and simplifying the configuration of required sleeves. In inline engines, parallel twin turbos are often applied with two small turbos that can provide performance not dissimilar to a single turbo, but it does reduce turbo response time. Some examples of inline twin-turbo engines include Nissan's RB26DETT, BMW's N54, and Volvo's B6284T and B6294T. Some examples of V-parallel twin-turbo engines are Mitsubishi's 6A12TT, 6A13TT and 6G72TT, Nissan's VG30DETT and VR38DETT and the B5 in the 1997 to 2002 S4, the 1997 to 2005 A6 and the 2003 to 2017 RS 6 from Audi. With the parallel arrangement it is also possible to use more than 2 turbochargers. Two examples of such use are the Bugatti EB110 and the Bugatti Veyron, both with a multi-turbo engine with 4 turbochargers in parallel. The EB110 has 4 turbos in a 3.5-litre V12 engine putting out 542 PS (404 kW) at 8,000 rpm, while the Veyron mounts them in an 8.0-litre 16-cylinder putting out 1,001 PS (736.2 kW). The Super Sport version of the Veyron mounts 4 turbos in an 8.0L W-16-cylinder engine that puts out 1,216 PS (894.4 kW).

Sequential turbo

BMW 3 Series diesel engine (sequential drum)

The configuration of a sequential turbocharged engine consists of using one turbo for low speeds and a second turbo for high speeds where the engine needs to boost its performance. Generally these engines are not very efficient at low revs, so the intake pressure is lower in such conditions. However, small turbos do fine at low revs, but they can't handle the amount of air being taken in at high speeds. During low and medium speeds there is only a relatively small turbo running (called the main turbo). During this period all the energy passes through that turbo producing benefits such as a reduction of turbolag and giving better responses at low speeds. As revs rise, the second turbo kicks in partially to 'warm up' the engine. before its full entrance on the scene. Once a preset engine speed and turbo pressure is reached, the valves that control the second turbo's compressor and turbine are fully open. At this point the first turbo is deactivated, so it doesn't suffer from the high amounts of air intake. From now on the benefits of having a larger turbo are increased, including more power and without the disadvantage of increased turbolag.

Sequential turbos provide a way to reduce turbolag without compromising turbo power. The most notable applications of this configuration can be seen in engines such as the fourth generation Toyota Supra (from 1993 to 1998), the Porsche 959 from 1986 to 1988, Mazda's Eunos Cosmo JC from 1990 to 1995, the 13B-REW of the Mazda RX -3rd generation 7 FD3S Turbo from 1992 to 2002, the EJ20TT from the 2nd generation twin-turbo Subaru Legacy from 1994 to 2005, and the 2.2 HDi from the Peugeot 407. GeneralMotors paid off the patent for the sequential twin-turbo engine and now uses a new bypass valve that optimizes exhaust flow from the turbines of both turbos.

Turbo by stages

A sequential turbo system can also be used to provide much higher output pressure than a single turbo, this is known as a twin turbo staged system. In this case multiple turbos of similar size are used sequentially, but operating constantly. The first one increases the pressure as high as possible (for example, 3 times the standard) and the following turbos take the charge from the previous turbo stage to compress it (for example, about 3 times the intake pressure, for a total of 9 times atmospheric pressure). This configuration is widely used in aeronautical piston engines, which do not require fast acceleration or low engine revs (where turbolag reduction is not a major concern) and where intake pressure It is less, due to the low atmospheric pressures that exist at the heights in which the engine of an airplane performs its power.

Some high performance diesel engines also use this configuration, since diesel engines do not suffer from pre-ignition problems and can work with significantly higher pressures than Otto engines.

Types of biturbo cars

There are several types of biturbo cars, distinguished according to the fuel or the category of the car. For example, there are twin-turbo gasoline cars, but there are also twin-turbo diesel cars. In both cases the advantages are the same: power, low consumption and safety. They can also be classified according to their category, high, medium or low. Since there are biturbo cars of all kinds such as a Volkswagen Passat BiTDi with 240 CV, or the Ferrari 488 GTB, with more than 550 CV. There are also SUV models, such as the Ford Edge with 238 hp.

These cars are designed for those who want a powerful engine, but also seek efficiency. Bi-turbo cars also differ in their operation, since there are versions with two different-sized turbos, a small one to act at low speed and a large one for high speed. A system that guarantees the best possible engine performance, even if it has a small displacement.

Advantages of a biturbo car

Twin-turbo cars have some advantages over a conventional car. On the one hand, its greater power, which not only makes the car faster, but also allows dangerous maneuvers such as overtaking with great safety. You just have to put your foot down on the accelerator. It also has the advantages that its engines are usually smaller, since being biturbo you can get a lot of power, without the need for a large engine. Thus, contained consumption is also achieved.

In addition, biturbo cars are cars that have a chassis prepared for high power, with bigger brakes and stiffer suspensions. Thanks to this, any biturbo car is safer than a conventional car. Sometimes they have an automatic gearbox, and are more comfortable to drive by not having to change gear.

Advantages in diesel emissions

A sequential turbo layout in a diesel engine reduces exhaust emissions considerably, which is why several diesel engine manufacturers have already opted to apply a sequential turbo setup.