Some potentially bad news for small-displacement turbocharged engines: Today Consumer Reports delivered their test results on a wide swath of new cars with small turbo engines. The verdict: Generally, CR says, turbocharged cars not only performed worse than naturally aspirated autos in the same segment, but also failed to meet their own EPA fuel-economy estimates. The most egregious underachiever, they say, is the Ecoboost Ford Fusion.
The performance part of the study shouldn't come as a great surprise. Turbocharged and naturally aspirated engines vary little in combustion efficiency, so both powertrains require about the same amount of fuel to produce the same number of ponies. As a result, bolting on a turbo to a slightly smaller engine doesn't instantly translate into better performance; it just lets the driver tap into an extra boost at higher RPM's. In this regard, when Consumer Reports compares Fusion's 178-hp turbocharged inline-four to Hyundai's 200-hp Sonata?well, of course the 0-60 times aren't going to be equal. The same goes when comparing 2.0-liter turbocharged I-4's: Ford's puts out 240 hp while Hyundai's tops out at 274, and, no surprise, the Hyundai is faster.
In terms of fuel economy, though, one would think that the smaller displacement turbos should win out. A 2.4-liter naturally aspirated car will always move 2.4-liters, no matter how light you are on the gas; an equally-powered turbo will move only 1.8-liters under light engine load (read: low RPM). It's surprising, then, that Consumer Reports found every single turbo engine to slightly fall behind their EPA estimates (though, to be fair, CR's data indicates a few NA cars weren't up to snuff either.)
One possible explanation for the apparent industry-wide discrepancy is not that turbocharged engines are inherently flawed, but rather that the EPA testing procedures might be. In a previous high-mileage test, PopMech noted that the government's tests are "surprisingly slow and short?the longest is 11 miles, and the highest average speed is 48 mph." While the EPA applies mathematical formulas to try and bring down the abnormally high fuel economy figures it gets this way, such slow-accelerating tests might never really stress engines enough that the turbo generates any meaningful boost, and in doing so consumes more fuel. Essentially, the EPA tests are measuring the fuel economy of the un-boosted engine?which, in the lab, will always be much more fuel efficient than a larger displacement motor.
So, inflated hype for small turbo engines? That's still up for debate. Inflated EPA economy figures? Quite possibly.