Cylinder deactivation helps automakers squeeze better fuel economy out of larger engines by cutting off some cylinders under light loads. Systems in production now typically deactivate no more than half of an engine's cylinders, but three companies are collaborating on a new one that takes a more aggressive approach.

Called Dynamic Skip Fire (DSF), the prototype system allows a V-8 engine to run on as few as two cylinders while cruising at highway speeds. It's based on an algorithm created by Silicon Valley startup Tula Technologies, and is being developed in partnership with General Motors Company [NYSE:GM] and Delphi, according to Automotive News (subscription required).

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The companies believe DSF could improve fuel economy by up to 21 percent, and reduce emissions by nearly the same amount. It operates on all cylinders, and can vary which cylinders get turned off to maintain proper operating temperatures and smoothness. Cylinders are reactivated as needed, essentially in response to how hard the driver pushes the accelerator pedal.

Tula claims that a V-8 SUV—like the GMC Yukon Denali it uses to demonstrate the system—only requires 30 horsepower to maintain a steady cruise at highway speeds. Apparently, that can be maintained with six of the eight cylinders shut off.

DSF can work on most gasoline engine types where there are four or more cylinders, according to Jeff Owens, Delphi's chief technology officer. It also uses cylinder-deactivation hardware already installed on some production engines, which could help lower costs.

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GM's stock cylinder-deactivation system uses special lifters that stop the flow of oil to valves. A 16-valve V-8 has them on eight valves, and upgrading it to DSF would simply requiring adding them to all valves, as well as some system-specific software. Depending on displacement, adding DSF would cost $300 to $600 per engine, according to estimates from Delphi and Tula. Delphi CTO Owens believes the system could be installed in production cars by 2020.


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