twinscroll

Twin-scroll, often written as twinscroll, refers to a turbocharger design that uses two separate exhaust gas inlets (volutes) feeding a single turbine wheel. The division allows exhaust pulses from paired cylinders to reach the turbine with less interference, enabling more efficient energy extraction from the exhaust and improving throttle response and low- to mid-range torque.

Mechanism and operation: The turbine housing is split into two scrolls, each receiving exhaust from a subset of cylinders. This separation reduces pulse stacking and back-pressure, helping the turbine spool more quickly. In inline engines, cylinders are grouped to feed the two scrolls (for example, alternating cylinders or paired groups). In V-engines, cylinders from opposite banks are typically arranged to balance exhaust pulses. The result is smoother turbine operation and improved transient response compared with a traditional single-scroll setup.

Usage and applications: Twin-scroll turbochargers have become common in modern gasoline and diesel engines as a way to improve efficiency without sacrificing low-end power. They are employed across a range of configurations, from small four-cylinders to larger six- and eight-cylinder layouts, as part of broader efforts to reduce turbo lag and optimize fuel economy.

Advantages and limitations: The main benefits include stronger low-end torque, quicker spool, and better overall efficiency due to more effective use of exhaust energy. Drawbacks include higher cost and complexity, more demanding packaging requirements, and diminishing returns on engines where exhaust-pulse timing cannot be effectively managed or where a simpler turbo design suffices.