What kind of engine is a twin-turbo?

We are talking about a modified turbocharging system installed on the internal combustion engine. Twin Turbo is the commercial name for the equipment. The phrase Biturbo is also sometimes used (some motorists mean by this a parallel-type design, which will be discussed later). The improvement of the turbocharging system was necessary in order to solve the key problem of such power units: the formation of the so-called. "pits" (turbo-lag) - power dips at low crankshaft speed.


This "nuisance" is due to the impeller, which is made of heat-resistant, heavy materials. As a result, the node has a decent mass and, accordingly, inertia. Even the most high-tech rotary motors with ceramic blades spin up relatively slowly. This negatively affects the dynamics of the car, and ultimately the safety of driving. If we talk about sensations, then the "pit" manifests itself as a push when moving away from a place or shifting gears.

In order to make the torque range wider, simultaneously reducing fuel consumption and increasing power, they began to use a dual turbine. The system can be implemented according to one of three schemes, each of which has its own configuration, parameters and operating principle. The entire system is controlled by an electronic module that receives information from sensors and sends command signals to actuators and valves.

Twin Turbo parallel type

This includes a pair of compressors operating at the same time. The flow of exhaust gases is evenly distributed between them. In each supercharger, it is compressed and then goes into the intake tract through the cylinders.

A similar system is most often found on V-shaped power plants. It’s more convenient: each of the two exhaust manifolds has its own compressor. The efficiency of the scheme is due to the fact that a pair of small turbines have less inertia compared to one large one. As a result, the "pit" is not so "deep" - the compressors quickly increase the boost pressure.

An example is Japanese car Mitsubishi 3000GT, produced from 1990 to 2000. Here, each of the two compressors takes gases from three cylinders (there are six in total) and then "blows" into a common manifold. The model, produced in 1994-1996, had a power unit volume of 2,972 liters, developing 324 hp. Torque of 427 Nm was achieved already at 2500 rpm.

Series Twin Turbo

Here, too, a pair of turbochargers, approximately equal in their characteristics. The first one functions without shutting down, the other one comes into operation as needed: when the load value changes, the number of revolutions of the crankshaft changes. To make the transition imperceptible and optimal, microelectronics are used, with the help of which the exhaust gases from one compressor to another go through a special valve. If it is kept open all the time, the parallel system described above will result.



The series version of the circuit minimizes turbo lag and promotes rapid power delivery. The system can be seen on both petrol and diesel powertrains from a variety of automakers. However, BMW went further - in 2011, Bavarian engineers introduced a sequential turbocharging design with three compressors, which they called the Triple Turbo (N57S). But everyone was outdone by the designers who installed four superchargers on the Bugatti EB110 in 1991-1995, the Bugatti Veyron in 2005-2012 and the Bugatti Chiron in 2016.

Step system (twin scroll)

It is considered the most "advanced" compared to the previous two and has been used since 2004. The scheme involves the use of a pair of compressors of different capacities, installed in series. The system works like this:

• ✅ at idle or low speeds, the exhaust passes through a smaller compressor: thanks to a special valve, the path to a stronger unit is closed
  
• ✅ with an increase in the number of revolutions, the small turbine begins to spin up, the pressure increases and the valve opens slightly, falling on the impeller of the large turbine, which begins to rotate
  
• ✅ pressing further on the gas, the driver increases the pressure in the system even more and the valve opens more
  
• ✅ when approaching maximum speed, the small turbine is deactivated, because it simply starts to interfere with the large one and the gas flow goes directly to a more powerful supercharger
  

A similar version of the Twin Turbo has been successfully used on the Subaru Legacy B4 RSK (1998-2003). The model was equipped with a motor with this system, having a volume of 2 liters and developing a capacity of 280 "horses". Acceleration to "weave" took 5,7 seconds. on a manual transmission and 6,7 sec. with automatic transmission.

Advantages and disadvantages of Twin Turbo

Today, the system is in demand by developers of powerful machines. It ensures the implementation of the highest torque in almost the entire range of crankshaft speeds. Double supercharging allows you to get solid power with small engine dimensions, which saves fuel when compared with the "aspirated". There are other benefits worth mentioning:

• ✅ there are no "turbo-jams"
  
• ✅ the car becomes dynamic already at low engine speeds - the driver does not need to spin it up
  
• ✅ the load on the power unit drops: less lubricant is consumed, the cooling system operates in a gentle mode
  
• ✅ Useful use of exhaust energy
  

However, there are also disadvantages that do not contribute to the widespread adoption of twin turbocharging. Main cons:

• ✅ complex design, it is clearly visible on the most "advanced" engines with Twin Turbo
  
• ✅ high cost of the power unit and high cost of maintenance
  
• ✅ unreliability of the system due to the presence of a large number of components and parts
  

Sometimes finding the right parts and a turbocharged mechanic turns into a problem, especially if the car owner lives in a remote area. This must be taken into account when buying a car or equipping it with a supercharged unit.

How to extend engine life with Twin Turbo

The operating conditions, the climate of the region where the car will drive are important. This air injection system is more sensitive to the presence of lubrication than atmospheric engines. You need to be more careful with Twin Turbo if the car is in an area with a low temperature. At night, when the motor is not running, the grease flows into the sump and components, the system elements dry out. If you start the engine in the morning and immediately give a load, you can “kill” the supercharger. Therefore, before you put pressure on the gas, you need to let the car run at low speeds. Then the oil will thin and reach the most remote areas requiring lubrication. Do not forget: the turbine impeller heats up to several thousand degrees due to constant contact with exhaust gases, and the oil in this case not only has a lubricating function, but also cools.

And the last factor affecting the resource of the dual boost system is the quality of the fuel. If it is low, a layer of soot will quickly form on the impeller, which will make the structure heavier and lead to its destruction.