Range-extended electric cars are a great idea, mixing clean electric running for the majority of drivers' commutes, with an extra few hundred miles of gasoline running for those longer trips.
As we alluded to last week though, the engine isn't always perfectly optimized for its task, often a standard car unit designed for standard car requirements.
That could change with the next Chevy Volt and Cadillac ELR, which Edmunds reports may get a smaller, three-cylinder engine in place of the current car's 1.4-liter four-cylinder.
It's part of a plan to reduce both the fuel consumption and weight of GM vehicles by 2016, and the new engine would see service in a facelifted Volt, due in 2015.
Sources suggest the new range-extender will be either 1.0 or 1.2-liters in capacity, with three cylinders.
GM will be the latest carmaker to tackle three-cylinder engines, which are increasing in popularity in smaller vehicles across the world.
Traditionally the preserve of tiny city cars like the Smart Fortwo, compact three-cylinder engines are now appearing in a much wider range of vehicles. Most publicized recently is Ford's 1.0-liter Ecoboost 3-cyl, providing a more efficient alternative to the standard 1.6-liter unit in the Fiesta.
BMW has also teased a 1.5-liter 3-pot, which could see service in MINIs, 1-Series and 3-Series models (depending on the market) and also the i8 plug-in hybrid sports car. In Europe, virtually every manufacturer offers at least one car with a three-cylinder powerplant.
Most manufacturers have reduced the extra vibration inherent in three-cylinder units, and the new engine's size and weight should be lower than that currently used in the Volt.
At a Houston energy conference last week, GM Chairman Dan Akerson said, "A good rule of thumb is that a 10 percent reduction in curb weight will reduce fuel consumption by about 6.5 percent. Our target is to reduce weight by up to 15 percent."
As a smaller engine with less internal friction, it should also make the Volt and ELR's range-extended modes more efficient, additional to the gains from lower weight.
GM hasn't confirmed the 3-cylinder's use yet, and actual specifications are still hazy. Should the engine's development go to plan though, the next Volt could see large efficiency improvements over the current car.