When Cadillac introduced its all-new CT6 sedan at the New York Auto Show several weeks ago, it detailed 265-hp four-cylinder turbo and 400-hp twin-turbo V6 engine options. At the Shanghai auto show last week, it announced another powertrain option: a 335-hp plug-in hybrid powertrain set to double the fuel economy over the ICE alternatives.

One of the big selling points of the CT6 is that its lightweight Omega architecture gives it the size and spaciousness of a true luxury flagship, but the weight of a smaller car. Those weight savings make it ripe for an alternative powertrain. GM's solution uses a dual-motor, rear-mounted electric variable transmission (EVT) system, an 18.4-kWh lithium-ion battery pack between the trunk and rear seats, and a 2.0-liter turbocharged four-cylinder. The system puts out a total of 335 hp (250 kW) and 432 lb-ft (586 Nm) of torque.

"The first-ever CT6 is a technological showcase throughout, making it an ideal platform for Cadillac to offer its first plug-in hybrid,” said Cadillac president Johan de Nysschen. "The advanced Plug-In Hybrid system is a key addition, providing a combination of exceptional fuel economy, crisp acceleration and strong electric-driving range."

Cadillac is holding off on estimating the all-electric range, but it did say that it will be enough for "most daily commutes," which sounds similar to the "80 percent of Americans driving fewer than 40 miles each day" that GM was using back at Chevy Volt launch time, although it was in Shanghai this time around. We expect to see an all-electric range in that 40-mile (64-km) ballpark, and reports from sources like Automotive News put the number at 37 miles (60 km). Cadillac also expects the plug-in system to offer more than double the fuel economy of the CT6's gas powertrains, as measured in mpg-e.

GM promises that the two rear motors will deliver "smooth, spirited acceleration." The CT6 PHEV will run in three different driving modes: Normal, the everyday commuter mode designed to blend comfort, performance and fuel economy; Sport, with more aggressive pedal mapping and stiffer steering response; and Hold, which reserves battery power for later use. The car will also feature Cadillac's paddle-shift Regen On Demand feature, also used in the ELR and new Chevy Volt, along with traditional regenerative braking.

GM will begin production of the standard CT6 later this year, with the PHEV expected to follow in 2016. Pricing has yet to be released.

View gallery - 14 images