It's been one of the most-asked questions about the 2011 Chevrolet Volt extended-range electric car: So what kind of gas mileage will it get?

Despite confusion around Chevy's claim of 230 miles per gallon, what people wanted to know was simple: After the battery is depleted, when the car's gasoline-powered generator switches on, what gas mileage does it get?

2011 Chevrolet Volt

2011 Chevrolet Volt

First Chevrolet Volt battery pack built at Brownstown Township plant, January 2010

First Chevrolet Volt battery pack built at Brownstown Township plant, January 2010

Now we have an answer. The Volt's chief engineer, Andrew Farah, said in a briefing yesterday that not only was the 2011 Volt achieving its target of 40 miles of electric range, but it was also meeting the goal of 50 miles per gallon in so-called range-extending mode.

GM has long said that unlike pure electric cars--for example, the 2011 Nissan Leaf, which has a range of up to 100 miles--the Chevy Volt will have the cruising range of a standard car, which it has said will be "at least 300 miles" on top of the 40 miles on electricity.

Its range is extended when the 1.4-liter four-cylinder engine starts up after that 40 miles. But the torque it produces is used solely to turn a generator that sends power to the electric motor turning the front wheels; the engine does not mechanically power the car.

Fleets of pre-production Volts have logged more than half a million miles, including cold weather testing in Kapuskasing, Ontario, Canada--a traditional evaluation site due to its Arctic location--with hot weather tests coming this summer in Yuma, Arizona.

The first Volt traveled down the production line in Hamtramck, Michigan, at the end of last month, and Farah said everything is on schedule for regular production to start in the fourth quarter of this year (October through December).

The Volt's lithium-ion battery pack design has undergone the equivalent of 850,000 miles of testing in GM's battery lab. The first production packs were assembled at the Brownstown plant in January.

Farah also noted that General Motors continues to discuss with the U.S. Environmental Protection Agency how to rate the Chevrolet Volt's "gas mileage," so that standards for window stickers are ready by the time the car goes on sale in November or December.

[Detroit News]