Variations on a Vane: How Turbochargers Are Getting Better, Faster, Stronger

2016 BMW 328i M Sport

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From the June 2016 issue

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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:

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SEQUENTIAL TURBOS

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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😄 diesel, Audi SQ7 TDI

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TWIN SCROLL

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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

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VARIABLE-GEOMETRY TURBINE

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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

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TWIN TURBOS

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Two equal-sized blowers are each fed by half an engine’s cylinders. Using two turbos rather than one leads to smaller turbine and compressor wheels that spool quicker due to their lower inertia.
–Found in: Ford F-150 EcoBoost

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• 2018 Audi SQ7 TDI: The Superest Diesel SUV

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• 2016 BMW 328i Instrumented Test

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• First Drive: 2017 Porsche 911 Turbo / Turbo S

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OVERBOOST

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A temporary increase in boost pressure raises power, torque, and exhaust temperatures. Overboost is typically limited to 10-to-20-second spurts to avoid overheating components and causing catastrophic failure.
–Found in: Ford Focus ST

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from Car and Driver Blog http://blog.caranddriver.com/variations-on-a-vane-how-turbochargers-are-getting-better-faster-stronger/