Sequential Twin Turbo

"Sequential Twin Turbo" is another configuration used in turbocharged engines, but it operates differently from parallel twin turbos. Here's how it works:

1. Sequential Configuration: In a sequential twin turbo setup, there are two turbochargers of different sizes. These turbochargers are arranged in a sequence where one turbocharger operates at lower engine speeds (low RPM) and the other comes into operation at higher engine speeds (high RPM).
2. Operation: Typically, the smaller turbocharger (often referred to as the "primary" or "first-stage" turbo) starts boosting air intake at lower RPMs. This smaller turbocharger can spool up quickly due to its smaller size, reducing turbo lag and providing immediate power and responsiveness at lower engine speeds.
3. Transition: As engine speed increases, a valve or mechanism redirects exhaust gases to the larger turbocharger (often called the "secondary" or "second-stage" turbo). This larger turbocharger can handle higher volumes of exhaust gases at higher RPMs, providing increased airflow and power output at higher engine speeds.
4. Benefits: The sequential twin turbo setup aims to provide a broader power band by optimizing turbocharger performance across a range of engine speeds. It balances the responsiveness of a smaller turbocharger with the high-end power of a larger turbocharger, offering both quick acceleration and sustained power at higher speeds.
5. Examples: Vehicles like the Toyota Supra MK4 (JZA80) and some generations of the Porsche 911 Turbo have used sequential twin turbo setups to achieve a balance of performance and efficiency.

In summary, sequential twin turbos are designed to optimize performance across different engine speeds by using two turbochargers of varying sizes that operate sequentially to provide responsive acceleration and strong top-end power.