Turbochargers are—literally—spooling up, with every major automaker now offering at least one boosted model in their lineups (and one with four turbos). 

Today, our friend Jason Fenske over at Engineering Explained takes a look at the most cutting edge variation: the variable twin-scroll unit. Developed by Borg-Warner, the variable twin-scroll combines two different technologies in an effort to improve both performance and fuel efficiency.

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As he always does, Jason takes a complicated subject and presents it in a simple, organized fashion. With his increasingly famous white board, he breaks down just what makes this type of turbo a more effective way of adding power to an engine.

In short, the Borg Warner setup has a special valve that can apportion airflow from the vehicle's exhaust between either a single scroll or twin scroll. Each offers its own advantages, depending on the engine and how hard it needs to work to motivate a vehicle.   

The overall advantage here is that the valve allows automakers to utilize less exotic materials for a variable geometry turbocharger to work in a gas engine, where exhaust temperatures can be very high. This means that variable twin-scroll turbochargers could be feasible for use in a wide range of vehicles at a reasonable price point.


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