Probably the single biggest mystery for the 2016 Volt is how much electric range it will get.

That’s still a mystery, but GM told SAE International the completely revised Voltec powertrain will provide 12-percent improved range and energy usage.

All things being equal, that would boost the existing 2015 model’s 380 gas-plus-electric miles to 425 miles but for Volt owners this is far less important than all-electric range.

“Greater range (particularly in EV mode), fuel efficiency, and power were the top three requests from owners of 2011-2013 Volt models,” said a report by SAE International citing Larry Nitz, GM’s Executive Director, Transmission and Electrification.

So, is it reasonable to say if it’s 12 percent overall, and better in EV mode than gas mode, that EV range was boosted by more than 12 percent? Not sure, but if so, a 12-percent increase over 38 miles is 42.5 miles, so “greater” than this means EV range could be 43-plus.

Of course everyone already suspects as much, and guesstimates have been from the high 40s to 50-60 range, but the otherwise vague disclosure of 12 percent is another solid clue, at least.

A Nissan Leaf gets up to 84 rated miles, but being an EV, it cannot run to empty, so if it’s safe at 70ish, a revised Volt with perhaps 65-70 percent the range – plus gas backup – threatens to make quite a case for itself, depending on how much they price it for.

As for fuel mileage, the 2015 Volt was rated at 37 mpg combined in gas operation. The 2016 will run on regular, not premium, and a 12-percent increase would boost the old car’s 37 to 41.4 mpg, which might mean 41-42 on the sticker, but this too was not disclosed.

A Toyota Prius Liftback is rated at 50 mpg and next year will be improved with generation four.

GM is withholding specific efficiency numbers until the Detroit reveal, but does say it responded to its pool of Volt-owning drivers who gave extensive feedback for GM to re-engineer the powertrain.

There is one misreport floating out there saying the SAE was told the 2016 Volt will keep the 2015’s “16″ kilowatt-hour pack capacity for its redesigned pack, but this is certainly incorrect as the 2015 has 17.1 kwh.

The specific capacity of the pack was not disclosed by SAE International’s report, but as reported earlier it’s 30-percent lighter, and has a reduced number of cells from 288 to 192 (still 96 cells in series).

Actually the whole Voltec powertrain is a fresh start, and also now 130 pounds lighter with the 1.5-liter’s aluminum block accounting for a good chunk next to the iron block of the outgoing 1.4 liter.

“I can’t think of a powertrain we’ve re-engineered more extensively within a five-year period than this one,” said Nitz to SAE International.

A revised TPIM (traction power inverter module) is now direct mounted to the transmission case eliminating the heavy orange 400-A cables. GM said the focus was system integration.

SEE ALSO: 2016 Volt Gets Improved Range And Efficiency

The 1.5 liter reduces NVH (noise, vibration and harshness) and the 1.0-liter turbo everyone thought was going to be installed was unacceptably noisy at points, especially at start up.

In all, efficiencies were found in re-vamping much of the system which now uses two redesigned motors. The new Volt has 20-percent more low-end power, is lighter, quieter, has more range.

Unanswered is anything about a fifth seat, and of course a breakdown of the range and efficiency numbers. The actual details will be announced in January unless some other leak happens sooner.

SAE International