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Do Small Turbo Engines Really Give Better Gas Mileage?

 
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2014 Ford Fiesta: EcoBoost (European version)

2014 Ford Fiesta: EcoBoost (European version)

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Back in November, we asked whether tinier, turbocharged engines were really the best way to get good gas mileage.

Our assertion was that with the latest generation of small turbocharged engines replacing larger variants, the real-world gas mileage improvement is nowhere near that of the on-paper advantage in official economy tests.

Unsurprisingly, we've not been the only ones to notice.

Thorough testing by Consumer Reports has revealed the same issues with downsized, turbocharged engines across the automotive spectrum.

Downsizing = little efficiency gain

In CR's hands, Ecoboost Ford Fusions using turbocharged, four-cylinder engines, have achieved worse mileage and worse performance than larger, naturally-aspirated counterparts. The four-cylinder engine in the 2.0 Ecoboost also loses out on refinement to the typical V-6 units in the class.

The results are similar, though not as extreme, with the Chevrolet Cruze. Testing has revealed both the 1.4 turbo and 1.8 naturally-aspirated models to get the same 26 mpg, while the 1.4 was only marginally faster. In the Dodge Dart, the turbocharged 1.4 was much quicker than the 2.0 model, but only 2 mpg better on gas mileage.

Perhaps most galling is the 2.0 Ecoboost Ford Escape, slower to 60mph by 1.5 seconds than a 3.5-liter V-6-engined Toyota RAV4, but attaining an identical 22 mpg. Even the Ford's EPA rating is only 2 mpg better than the Toyota's.

It's a similar story with trucks. As we noted in our original piece, Ford F-Series drivers are getting a real-world 17 mpg whether they choose the 3.5 Ecoboost or the traditional 5.0-liter V-8. Both cars get a real-world 15 mpg in Consumer Reports' testing.

What's more, buyers are usually expected to pay more for these newer, more high-tech powerplants, making them something of a false economy.

Fiat 500 TwinAir two-cylinder engine

Fiat 500 TwinAir two-cylinder engine

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It's a trend European buyers have already seen with the tiny Fiat Twinair and Ford 1.0 Ecoboost engines. Both are fantastic works of engineering, but deliver limited gains in the real world, while costing more than less advanced equivalents.

Sound principles

The theory behind downsized engines makes sense. While you may not gain on performance next to the larger engine you're replacing, you won't lose any either--yet a smaller capacity engine should allow your gas mileage to improve.

A turbocharger makes up for lost capacity in smaller engines, but unless driven in a very specific way, the efficiency gains can be minimal. To achieve performance parity the engine still needs to pump extra air into the engine, and this is matched by extra fuel.

Drive carefully and there are gains to be had--but then driving any vehicle with economy in mind can bring about improvements.

CR recommends you look elsewhere for true gas mileage gains, such as hybrids and diesels.

We'd echo this to some extent, though it is worth pointing out that some of these new turbocharged engines can be a lot of fun, sometimes more so than the units they replace--so if you need the dual priorities of efficiency and performance, they could be worth a look.

Just don't be too disappointed when you see your gas mileage tumble...

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Comments (14)
  1. Well that is disappointing.
     
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  2. That is physics...

    Typically, the smaller engine with turbo does gives you some weight saving, which will translate into better handling and better acceleration and maybe better economy. But the displacement between 1.6 and 2.0 aren't really all that large. Even the weight between 1.6 and 2.5 aren't all that great...
     
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  3. Driving along the highway here in Slovakia I've seen many billboards from Ford, proudly claiming "Najlepsie motor na svet!" (The best motor in the world!) with a new Ford Focus in the picture.
    So if the above article is true, then the ecoboost engine is no better in real world testing than any other engine. It turns out my scoffing was well founded.
    Once again it seems the best motor in the world in terms of power, emissions, and economy is an electric motor.
     
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  4. As you show here. http://www.kiwiev.com/random/V6%20versus%20EcoBoost%20versus%20Electric%20Motor%20Comparison%20from%20Ford.jpg
     
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  5. Poorly written article. How often do we see a manufacturer use the same engine in 2 different vehicles with differing mpg's in each? Tweaking an engine, connecting it to different transmissions with different ratios and body weight can all effect mpg's. The fact that these smaller, turbo-charged engines make small improvements in the right direction, they are still improvements in the "right direction". The vast number of improvements in mileage come from small steps that over time and with combined with other small improvements, create larger gains.
     
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  6. The argument for small engines is when you are not at full power you have fewer fewer and/or smaller pistons and camshafts hence less inertia and friction which cause inefficiency. When you deliver full power, this is overtaken by the need to stuff air and gas one way or another. So the small turbo engines are much more on/off in their MPG than the bigger engines. So the advantage when you are driving economically is better than with larger engines. Similarly with hybrids, you have to change your driving style (e.g. brake early and progressively to charge vs slamming the brakes). With small turbos, hit the gas to get speed and then cruise as much as you can to get best MPG. Ignore this you and you get bad mileage with hybrid and turbos.
     
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  7. This is sure true with my 2000 Honda Insight. My girlfriend drives it with no care about gas mileage and gets around 45-50 mpg's. I drive the same route, barely any slower, just paying attention to the traffic lights and trying to glide whenever I can, and I get 25-30% better mileage that she does. It will be interesting to see how the car does in real world driving with people who make an effort to get the best mileage possible.
     
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  8. I will add this to, that the most wasteful thing she does along with so many other people around me on the road, is that she races to the stoplight as fast as she can just to sit there for 10 seconds till the light changes and do the whole thing over again at the next light!
     
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  9. That sounds like those traffic lights are designed by "grade D engineers" who have no brain on how a modern traffic light control should be...

    Most of the lights in my area are computer controlled and fairly good at keeping the traffic going.


    This is a clear example that a well designed road/traffic control can save much more fuel than any technology on cars...
     
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  10. They are controlled to a certain extent, depending on the direction you are going, and the time of day. But still, you'll get better mileage by paying attention to what is going on a couple of lights ahead of you. And you won't be going any slower overall than anybody else. And I understand it can be annoying to people who don't know what you are trying to do. People just don't seem to want to think it through as to what you are trying to do, which is keep your momentum up.
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  11. I agree that is obviously "dumb" to acclerate to the next light when it is clearly red or the exit coming up. But sometimes making it through the "next light" will also keep your momentum up while others get stuck behind idling for the next green.

    It is a balance... You are right, people should use "brains" on this. Obviously, the faster you accelerate, the more energy you will consume.

    My Wife gets about 3-4 miles less than I do when she drives my Volt. I already have a Pb foot and she has a U foot.
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  12. Poor article, small turbo engines deliver way better economy in real commuting world. It is good trend.
    Idling at red light or stop and go traffic, any slow moving in city with small cc engine returns significant better fuel economy and less polution.
    Japan had their under 1000cc turbo charged engines for decades.
    Also remember VW TSI was engine of the year, for good reason.
     
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  13. the problem is (I-havn't-counted-how-many)fold:

    1. Under boost, you lose theoretical/thermodynamic efficiency, and more on top due to running rich.
    2. The rest of the time, you lose efficiency because you've compromised compression and generally overengineered engine components.
    3. Having a turbo+ intercooler can make other parts inaccessible, and can fail of their own right too.

    People mentioning the equivalent-power NA engines are on the right track for the future, we just need great transmission designs to deal with the lack of torque. Power is power, if you can just use it.
     
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  14. well, i do think manufactures have a slightly wrong idea, efficiency is however way way up, which the author fails to mention, waste heat is used to increase compression, where the manufactures fail is rpm, a very small turbo to boost under highway cruising conditions and a larger power turbo would be a huge boost across the board. rpm is a major gas mileage factor and typically turbos boost under high rpm loads. and btw mr paul, factory boosted engines typically aim for 12:1 which might be the same as a n/a engine, heavy boost 11:1 is needed to cool the chamber, light load boost can be run stoich. the same as a normal engine, please consider that a typical engine only uses 30% of the fuel for pwr and 70% as waste heat 30% goes out the exha
     
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