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Hybrid-vehicle upstart Fisker Automotive Inc. pulls back the curtain on the advanced aluminum spaceframe construction of its upcoming Karma model at the Geneva auto show.

The plug-in Karma hybrid feature a 2.0L turbocharged Ecotec engine from General Motors Co. coupled with a 403-hp electric motor powered by a lithium-ion battery pack from A123 Systems.

Like the upcoming Chevrolet Volt, the Karma is a series hybrid that uses the gasoline engine solely for maintaining battery charge, not driving the wheels.

The car’s skeleton consists of 5,000- and 6,000-series aluminum alloys and utilizes unique extrusion techniques to achieve rigidity and minimize weight, the auto maker says.

The frame incorporates a tunnel down the centerline to house the batteries and act as a structural backbone that connects the front and rear sections of the car. It is joined with 259 ft. (79 m) of precision CMT MIG welds and 1,058 self-piercing rivets, Fisker says.

Static torsional rigidity measures more than 24,341 lbs.-ft. (33,000 Nm) per degree and static bending rigidity reaches more than 131,000 lbs./in. (23,000 N/mm), the auto maker says.

“Our top priorities when we designed the Karma’s aluminum spaceframe were that it have extremely high torsional rigidity and could be easily modified to accept Karma model variants,” CEO Henrik Fisker says in a statement.