General Motors made a stir earlier this year when it announced that the Chevy Volt plug-in hybrid would get the equivalent of an eye-popping 230 mpg in city driving, and over 100 mpg combined. Those figures were reached using a rather complicated calculation that takes into account the car's ability to travel 40 miles in all-electric mode, using no fuel at all.

But one of the mysteries of the Volt has been what kind of mileage it will get after those 40 miles, when the onboard internal combustion engine kicks in to provide electricity for the electric motor, allowing it to travel a total of 300 miles with a tank of fuel of an unspecified volume. While that exact figure is still unknown, the man in charge of the project has now opened up the gates to the ballpark.

In an interview on FoxNews.com's Fox Car Report LIVE! webcast, Volt Vehicle Line Director, Tony Posawatz revealed that the fuel economy will be "better than any conventional car, and we're trying to figure out how close, or if it will actually be better than any hybrids."

Click here to name the Volt's paint color

Currently, the most fuel-efficient non-hybrid or non-alternative-fuel vehicles are the much smaller Toyota Yaris and MINI Cooper, both with an EPA combined rating of 32 mpg. The Toyota Prius is the reigning mileage king at 50 mpg. Posawatz's statement would put the Volt's extended-range fuel economy squarely between those two figures, and possibly slightly higher than that of the Prius. But he added that the software that controls the car's powertrain is still being tweaked, and a final number is still to come.

A fleet of pre-production test vehicles recently completed a six-state "shakedown" drive on public roads, as well as a climb up Colorado's demanding Pike's Peak. Posawatz says the cars worked fine on the trip, with final adjustments being aimed at making the powertrain operate "seamlessly."

Click here for the full interview with Tony Posawatz

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