Let’s start with the basics – a single turbocharger is a “forced induction device that pushes more air into the combustion chamber of the engine, allowing for more fuel to be added”. This basically means you get more of a bang by re-using air from the exhaust gases of the engine, as these gases are used to power a turbine that drives a compressor. The additional explosions resulting from the extra air/fuel mixture gives us more power, therefore we go faster. Simple.
So, if one turbo gives us more power, then more turbos give us even more power. But at the expense of weight. Enter the twin scroll turbocharger.
Effectively you can think of this as two turbos inside one casing – each turbo utilises a different exhaust manifold (basically connected to a different set of cylinders) to ensure that we get smooth expelled air into our turbo inflow, and do not disrupt the exhaust pulses. A single turbo can suffer from a situation where one cylinder is expelling gas but another is just finishing its power stroke, so we get a turbulent airflow.
Twin scroll turbos can then be optimised for different rev ranges, giving us a smoother and wider power band.