From the June 2018 issue

You’ve heard the hypothesis before: Turbocharged cars miss their advertised fuel-economy figures more often and by larger margins than naturally aspirated cars. It’s a notion repeated so often that it verges on truth by consensus, possibly because it so easily fits with an intuitive explanation: Turbocharged small-displacement engines may be parsimonious on the EPA’s feather-footed driving cycles, but keeping up with traffic in the real world requires spooling the compressor and uncorking the fuel injectors.

That’s the theory. This is the test.

To settle the matter once and for all, we mined two data sets captured from 730 real-world drives of turbocharged and naturally aspirated gasoline vehicles. The first database consisted of 340 vehicles from Car and Driver’s highway-fuel-economy test, a 200-mile interstate slog run at an average speed of 75 mph. Analyzing each vehicle’s real-world fuel economy as a percentage of its EPA highway rating suggests that the popular belief isn’t actually true, at least when it comes to highway mpg. The data reveals that, on average, the 193 turbocharged vehicles we sampled actually beat their window stickers by 3.1 percent. Naturally aspirated models performed worse, only matching their labels on average. Half the free-breathing vehicles beat their EPA numbers, while the other half underperformed according to the label. Among turbo models, 65 percent topped their EPA highway ratings.

Car and Driver

Of course, steady-speed low-load highway cruising plays to the strengths of newer downsized and boosted engines that sip fuel while the turbo dozes. To see if boosted engines could stand up to more dynamic driving, we partnered with Emissions Analytics, an independent testing group that publishes its real-world fuel-economy and emissions EQUA Index at USA.EQUAIndex.com. The company uses a portable emissions-measurement system to sample a vehicle’s exhaust and derive fuel economy. Its 88-mile Southern California test loop includes both city and highway driving. Emissions Analytics uses a vehicle’s EPA combined mileage rating as its bogey.

Surveying the company’s 390 tests of turbocharged and naturally aspirated vehicles shows that the trend spotted in C/D’s highway fuel-economy data applies here as well. In Emissions Analytics’ testing, turbo vehicles beat their EPA labels by a slim margin on average (0.6 percent), and they also fared better than unboosted models, which fell short of their EPA marks by an average of 2.3 percent. Stop-and-go traffic dragged down turbocharged engines, but it did the same thing to naturally aspirated powertrains, too.

The takeaway? On bulk, turbocharged vehicles do live up to their fuel-economy labels. And they don’t suffer in the real world any more than naturally aspirated vehicles. That said, there are hundreds of cars, turbocharged and not, that exceed or fall short of the official fuel-economy numbers—some by 20 percent. The data largely vindicates the EPA’s fuel-economy methodology, but it’s an even stronger endorsement of that old axiom: Your mileage may vary.

This content is created and maintained by a third party, and imported onto this page to help users provide their email addresses. You may be able to find more information about this and similar content at piano.io