GM says its previous forecast of 230 miles per gallon for the Chevy Volt electric car is dead. It was calculated using a government formula that never got final approval and the feds are working on a new one.  "We just don't know right now" what the new number is likely to be, Micky Bly, executive director of global electrical systems for GM, said Wednesday at GM's battery factory in Brownstown, Mich.  In fact, talks with the government on how to calculate an mpg-equivalent index for plug-in electrics probably will continue until the very eve of Volt production in November, said Tom Stephens, GM's vice chairman of global product operations.  "We've been working collaboratively with the EPA and the industry to come up with a number that gives our customers something they can feel comfortable with," Stephens said.  There is no consensus on how to give buyers a number that lets them compare the energy use of electric cars -- including the cost to recharge them -- with the miles per gallon ratings of conventional gasoline and diesel vehicles.  The Society of Automotive Engineers, an organization the sets standards used by the industry to measure everything from horsepower to trunk space, is working on energy-use comparison standards for electrics. It recently approved a rating system for plug-in hybrids and says it will publish that standard, called SAE J1711, later this year.  SAE says it expects the government to use its standard for rating plug-in hybrids.  -- Sharon Silke Carty/Drive On  To report corrections and clarifications, contact Standards Editor  . For publication consideration in the newspaper, send comments to  . Include name, phone number, city and state for verification. To view our corrections, go to
Chevy Volt 230-mpg forecast dead; feds work on new formula  - Drive On: A conversation about the cars and trucks we drive - USATODAY.com