2016 BMW 328i M Sport
From the June 2016 issue
A turbocharger is basically a hair dryer that adds horsepower. An exhaust-driven turbine wheel spins a centrifugal air compressor to increase the amount of air fed into the cylinders. The additional air, combined with more fuel, boosts power and torque. The following technologies allow for greater output, increased efficiency, or lower lag compared with a single, basic turbocharger:

SEQUENTIAL TURBOS
Here, a smaller turbo spools quickly for low-end responsiveness while a larger unit boosts top-end power with higher volumes of exhaust. Sequential setups have fallen out of favor because they require complex controls and bulky packaging, and recent advances have reduced spool-up lag in single- and twin-turbo setups.
Found in: Nissan Titan XD diesel, Audi SQ7 TDI

TWIN SCROLL
The exhaust manifold and turbine housing split the exhaust into two segregated streams. This optimizes the timing of the exhaust pulses delivered to the turbine wheel, improving response when the throttle position changes abruptly.

Found in: BMW 328i

VARIABLE-GEOMETRY TURBINE
Movable vanes at the turbine inlet change the angle and speed of the exhaust gas before it arrives at the turbine wheel. At low flow rates, the vanes form narrow openings that accelerate the exhaust gas to reduce lag. Electric or pneumatic controls open the vanes to permit greater exhaust volumes to pass through at higher loads.

Found in: Porsche 911 Turbo

TWIN TURBOS
Two equal-siz...