Apparently very little. A Times reporter took one out for a test drive past its 40 mile battery range. What happens is that the gas-powered generator kicks in-silently-giving more battery power to the car. Its not as if you suddenly switch to a gas-powered engine; you're still using electric power, just not stored electric power. Indeed, even while the generator is on, accelerating is silent, as you're just putting more battery power into the engine, not revving the generator.The test drive found some kinks still to work out (sometimes the generator becomes not silent, but very, very loud), but this is a pretty exceptionally good review of what could be the car that changes a lot of things-both for the environment and the American automotive industry-when it's released in nine months.And here is an accompanying slideshow of Volt porn.