We’ve been following the Chevy Volt as it has progressed through many milestones before it became a development mule based on the 2011 Chevy Cruze last May. That test drive was completed entirely in electric-only mode. We experienced the car in both pure-electric and sustained-charge modes, in which the conventional gas engine powers an onboard alternator to supply the needs of the electric motor when the batteries reach an elected state of discharge. The Volt is still about a year away from production, with an intended launch date of November 2010.

The prototype Volt we drove in the parking lot of the Dodgers Stadium in downtown Los Angeles is what Farah calls a 65 percent write-off vehicle, meaning it’s about 65 percent of the way to full production standards. As such, it had a few  technical bugs already identified and rectified for future cars. Still, this prototype is a fully representative vehicle in terms of structure and drive train.

Electric propulsion systems are well-known for their smooth and quiet operation. So the unobtrusive cycling of a gasoline engine is considered a crucial aspect of this kind of hybrid system. Consumers simply won’t tolerate a system that doesn’t operate seamlessly. Here is how the Volt performed.

The Volt uses a three-phase AC induction motor rated at 120 kilowatts, or 160 hp, powered by a 6-foot-long, 375-pound array of lithium-ion cells mounted low along the Volt’s floorpan. Of course, weight mounted higher in the chassis would result in more noticeable roll. The engine is a normally aspirated 1.4-liter inline four-cylinder unit from GM’s global Family Zero range, manufactured in Flint, Mich., and it is hooked to a 53-kilowatt alternator to provide current for the Volt’s electric motor once the battery pack has discharged about halfway. To prolong battery life the cells are never allowed to recharge higher than about 80 percent of maximum, and they are never permitted to discharge more than about 50 percent unless an emergency occurs, and “limp-home mode” is triggered

The first few minutes of driving in pure electric mode proved the Volt is exceedingly smooth and quiet in the way it goes down the road. Indeed, the absence of mechanical clamor produces new challenges for noise, vibration and harshness engineers. Farah cited a redesign of a rear-suspension component as an example of issues that arise when the background sounds of a conventional engine and transmission are absent.

That happy state of affairs should last for 40 miles or so on a fully charged battery pack—enough to meet the round-trip commuting requirements of 80 percent of drivers. When the 1.4-liter inline four-cylinder engine cuts in during our drive, Farah is the first to notice it. We’re actually surprised to hear the news. That’s how subtly the gas engine makes its entrance. And in driving circumstances that only require modest throttle application, most occupants will probably not even notice it.