What is bi-turbo or parallel boost? [management]

Designers of V-engines would have a big problem pressurizing them with a single turbocharger. That is why a parallel boost system is often used, i.e. bi-turbo. I explain what it is.

Each turbocharger has an inertia due to the mass of the rotor, which must be accelerated by the exhaust gases. Before the exhaust gases reach a speed sufficient to rev the engine, what is known as turbo lag occurs. I wrote more about this phenomenon in the text about the variable geometry of the turbocharger. To understand the article below, it is enough to know that the more power we want or the larger the engine size, the larger the turbocharger we need, but the larger it is, the more difficult it is to control, which means more delay. in response to gas.

Two instead of one, that is. bi-turbo

For the Americans, the problem of supercharging V-engines was solved a long time ago, because they used the simplest possible solution, i.e. compressor driven directly from the crankshaft. The huge high power device has no turbo lag problems because it is not propelled by exhaust gases. Another thing is that, despite such supercharging, the engine still has the characteristics of an atmospheric one, because the compressor speed increases similarly to the engine speed. However, American units do not have problems with batches at low speeds due to large capacities.

The situation was completely different in Europe or Japan, where smaller units reign supreme, even if it is a V6 or V8. They work more efficiently with a turbocharger, but here the problem lies in the operation of two banks of cylinders with one turbocharger. To provide the right amount of air and boost pressure, it just needs to be big. And as we already know, a big one means a problem with the turbo lag.

Therefore, the issue was resolved with a bi-turbo system. It consists of processing two V-engine heads separately and adapting a suitable turbocharger to each. In the case of an engine such as a V6, we are talking about a turbocharger that only supports three cylinders and is therefore relatively small. The second row of cylinders is served by a second, identical turbocharger.

So, in summary, the parallel injection system is nothing more than the same two turbochargers serving one row of cylinders in engines with two heads (V-shaped or opposed). It is technically possible to use parallel charging of an in-line unit, but in such cases, the parallel charging system, aka twin-turbo, works better. However, some BMW 6-cylinder engines are parallel supercharged, with each turbocharger serving three cylinders.

Title problem

The bi-turbo nomenclature is used for parallel charging, but car and engine manufacturers do not always follow this rule. The name bi-turbo is also often used in the case of sequential topping up, the so-called. TV series. Therefore, it is impossible to rely on the names of car companies to recognize the type of supercharging. The only nomenclature that is not in doubt is serial and parallel replenishment.