Look, all technical mumbo-jumbo aside, turbocharging is actually a pretty simple concept. The objective here is to convert the energy contained in your exhaust stream, which would normally go to waste, into positive pressure within the intake manifold, forcing air into the engine and thus producing more power. Now, we understand this is a lot to cover--enough to write a book on--but the goal of this particular article is to get everyone, including readers who haven’t ever seen a turbo before, up to speed on the concepts involved. To put it bluntly, this is Turbochargers 101-A and covers the very tip of the iceberg, from 1,000 feet away. In this first article, we hope to establish a baseline vocabulary and a working knowledge with which to build off in the future, so if you’re an advanced turbo guru who is looking for tips reading compressor maps or tweaking turbine housings for your exact application, fear not--those stories are yet to come. For now, we’re going to cover the basics of turbocharging by looking at each component, defining its purpose, and explaining the theory behind its operation.
At the most basic level, a turbocharger consists of just three major components: the turbine, the compressor, and the bearing system that supports the turbine shaft, connecting the turbine and compressor wheels together. Understanding how all three parts work together is crucial, and even a basic understanding of the component’s relationships to one another will make selecting a turbo for your project much easier.
The turbine wheel is responsible for converting heat and pressure into rotational force. To understand how this process occurs, we would need to delve into some of the basic laws of thermodynamics, but within the scope of this article, understand that high pressure (from the exhaust manifold) will always seek low pressure and, within this process, the turbine wheel converts kinetic energy into rotation. As the turbine wheel rotates, it spins the turbine shaft, which in turn spins the compressor wheel. Often overlooked, turbine wheel selection is critical to a properly built turbocharger system, as having too small of a turbine wheel will induce excessive backpressure and can choke the engine, making it lose power. On the other hand, selecting too large of a turbine will result in increased lag and can make it difficult to achieve specific target boost numbers.
Of course, the turbine wheel doesn’t act alone. It is part of the turbine housing, which is that giant, sometimes rusty looking piece of iron or steel you always see bolted to an exhaust manifold or merge collector on a turbo car. Because of the tremendous heat involved in collecting and moving pressurized exhaust gasses, the turbine housing is constructed from thick iron or steel and always consists of a turbine foot (the flange which connects to the exhaust manifold piping), an outlet connection (the large opening that connects to the downpipe), and a volute, which is the path the hot exhaust travels to get across the turbine wheel, from the turbine foot to the outlet. When someone calls a turbo a "T4 turbo," they are talking about this flange. Exhaust enters from the flange, rotates around the wheel inside the volute, and exits across the outlet connection, into a piece of exhaust that enthusiasts call the downpipe.