The aim with the twin-turbo system is to adapt turbocharging pressure to the needs of the engine across all operating ranges.
To that end, two turbos are used sequentially. A small, low-inertia turbo that activates effortlessly from the lowest engine speeds provides torque, while a large turbo, sized to supply power at high engine speeds, kicks in when the gas flow rate rises.
At very low engine speeds, the strong action of the small turbo combines with the low action of the large turbo to generate a maximum amount of torque. The system supplies the engine with the right amount of turbocharging at all times, with no loss in responsiveness and no acceleration lags.