Powertrains for the Chevy Sonic are pretty much the same as in the larger Cruze sedan; there's a normally aspirated 1.8-liter four, or a turbocharged 1.4-liter four. A five-speed manual is standard with the 1.8-liter, while 1.4T versions get a standard six-speed; but in either case, the optional six-speed automatic transmission will be a popular choice.
Between the two, the 1.4T is by far the better choice, as it's stronger and more flexible, as well as more refined and fuel-efficient--and it makes the Sonic feel like a premium-brand vehicle, almost.
Power ratings aren't that much different between the two engines, there's a substantial difference in real-world performance. While both engines are rated at 138 horsepower, the 1.4T makes 23 pound-feet more torque—and it makes 90 percent of its peak torque all the way from 2,400 to 6,500 rpm, so you often don't truly need to downshift. It's also a very smooth, refined engine and feels a class above—although we tend to think that the throttle response can be a bit too muted or delayed.
If you're opting for the base 1.8-liter engine, take it out on the highway, up a grade or making some passes, to know what you're getting. It's not nearly as smooth, and tapping into the upper revs—necessary to extract the most power—brings a boomy, coarse character.
The six-speed manual gearbox is actually enjoyable with the 1.4T, with relatively short throws and direct, precise shift action, plus very smooth clutch takeup. So is the new six-speed automatic, which we found responsive and quick to downshift while just leaving it in Drive. You can control downshifts with a small plus/minus toggle button at the side of the shift lever. With either choice, though, consider that you'll be shifting more with the 1.8-liter engine.
Otherwise the Sonic is surprisingly enjoyable to drive for an affordable, economical car, with nicely weighted steering. A mushy brake feel (but good braking ability) in all the test Sonics we've experienced so far has been the worst offense.
RS models do get some key differences that make them even more enjoyable to drive. With a suspension that's retuned and lowered 10 mm, along with lower gear ratios, the RS should feel more sprightly; and a retuned exhaust provides the reinforcing soundtrack.