Getting Good Gas Mileage Is Hard; Will Tinier Engines Really Help? Page 2

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2010 Toyota Prius

2010 Toyota Prius

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Toyota knew this when it developed the 2010 Prius.

Compared with 2004-2009 models, it used a bigger engine--1.8 liters versus 1.5. Yet MPG still went up, and users on Fuelly are achieving a few mpg more despite having more performance.

While smaller engines should use less fuel (all other things being equal) many seem to struggle doing so when they also have to haul along a relatively heavy modern car body.

And they struggle even more in cut-and-thrust traffic, when the driver needs a little more performance. This is why many subcompacts achieve little better mileage than larger compact cars.

Caveat emptor

So how small is too small, then?

It clearly depends on the application, for a start. While a 900cc turbocharged engine in a Fiat 500 is no better than a 1.2-liter four-pot available in Europe, the 1.2 is recording figures almost 7 mpg better than the slightly larger 1.4-liter unit--so 1.2 liters is probably the sweet spot for the 500.

Likewise, the Toyota Prius may not necessarily be made more efficient by increasing the engine to a 2.0-liter unit. And buyers are over-achieving when it comes to economy in the 1.4-liter, turbocharged Chevrolet Cruze Eco.

But significantly downsizing to chase impressive EPA figures may not be as beneficial as it sounds.

Not only do many of these vehicles seem unable to match their figures in the real world, but the complicated, high-tech engines often cost a little more in the first place.

When the 2014 Ford Fiesta hits U.S. shores with the 1.0 EcoBoost engine and a headline efficiency figure, we'd advise you to treat it with suspicion--particularly given recent concerns over Fords missing their official EPA figures.

Of course, in the smaller, lighter Fiesta, the EcoBoost may be fine--which is really our point.

Some engines are better suited to some cars than others--buy too small, and "your mileage may vary" just a little more than you were expecting...


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Comments (45)
  1. You say: "On Fuelly, Ford F-150 drivers are averaging 17 mpg--both with the 3.5-liter V-6 EcoBoost engine, and the supposedly less efficient V-8."

    Antony - exactly where are you getting your numbers? Of the 499 gas V8 F150's currently being tracked on Fuelly, no model year with the V8 appears to be achieving 17 MPG (average).

  2. F-150, 2012, gas V8:

    F-150, 2012, gas V6 (most of which seem to be Ecoboost models):

    Largest sample of each is 17 mpg. Both have a range either side of that figure too. Safe to say that neither one is more economical than the other.

  3. The "largest sample of each is 17 mpg" does not equal "averaging" 17 MPG. ("Averaging being the word used in the article.) You can't cherry pick the peak of the distribution to prove your point!

    It's safe to say the actual averages (V8: 15.4 MPG / V6: 17.0 MPG) do not support your argument.

    And let's not forget that at the low end of the MPG scale, numerically small changes in MPG equate to significant volume differences: going from 15.4 to 17 MPG saves 92 gallons over 15k miles (typical distance/yr).

  4. 15.9 mpg versus 16.6 average, actually. 0.7 mpg in it between V-8 and V-6. (Yes, I'm aware gains are larger on inefficient vehicles).

    Full disclosure: I've removed the anomalous 31 and 45 mpg results from the V-6 one - we don't honestly think most drivers are likely to achieve that, right?

    It's daft saying I've "cherry picked", since it's entirely sensible to use largest sample as the basis of the results. If the majority of drivers hit a certain mpg, that rather suggests that it's a sensible, attainable figure.

    I'm aware I've used the word "averaging" but really we're reaching the realms of pedantry here - my point still stands. The V-6 is barely more efficient than the V-8 in real-world driving.

  5. "I've removed the anomalous 31 and 45 mpg results..."

    Right. And which anomalous results do we get to arbitrarily drop from the 1.0L EcoBoost Honest John "real world" average in order to make *that* number more accurate? Oh, right: none. (Because we have no useful details about that data.)

    I'm not defending either the outlying pickup truck numbers or the small Ford engine.

    But this exercise is pretty messy with the numbers.

  6. Darin - as I've already stated below, 1.0 sales make up a large proportion of the Focus models sold in the UK - 25%.

    It's absolutely reasonable to assume that the proportion of cars on there is no smaller than for any other model on that list.

    In addition (and AGAIN), it isn't just owners who are discovering the engine isn't particularly frugal in real-world driving - you can read similar data in pretty much any review you care to read.

    And AGAIN, the concept has precedents. The Fiat TwinAir being one.

  7. Ah the joy of “real world” data. People doing different things with their vehicles, making mistakes with their data, self-selection bias, and other issues. But you have to love data.
    Let me try a little different approach using Excel’s median function. Indeed “average” tends to weight bad data points too much, but “median” tends to ignore them.

    Ford F-150
    2012 16.5/16.2 mpg (V-6/V-8)
    2011 17.0/16.8 mpg (V-6/V-8)
    In each case, the V-6 is “better” but probably not in a statistically significant way as the difference is only 0.3 and 0.2 mpg. If we were “following the data” we might want to know why the 2012 models are lower mpg than the 2011, but again, this is probably not a statically significant difference.

  8. The EPA says it should be 18 versus 14 mpg for the V6 versus the V8 and there doesn’t seem to be much support for those numbers here.

  9. As well, here's a potential problem with using the Honest John site to report user-submitted fuel econonmy: the sample size is not reported when you view results for specific engine sizes. So, we have no way of knowing whether the Focus 1.0 average is based on 2 reports or 20, and should be very careful of drawing conclusions as a result!

  10. Ford 1.0 Ecoboost sales make up 25 percent of all Focus sales in the UK. We don't know the sample size for sure, but it's safe to assume that it's as large as any other engine size sample in the lists.

    Irrespective of this, it also reflects rather poorly on the engine regardless. And it's also data corroborated by several automotive magazines, all of which are struggling to get near the official numbers by the same - and occasionally greater - amounts.

  11. Also: comparing the "real world" MPG of the 1.0L Focus, you say:

    "It's also barely above that of the 33 mpg 2012 Ford Focus SFE sold in the U.S.--with its 2.0-liter engine."

    Apples and oranges! If one premise of this article is that "real world" MPG doesn't line up with the official ratings, why are you comparing real world numbers from the U.K. with the SFE's *EPA ratings*?

    This article started out with a *very* interesting question. Too bad it's undermined by sloppy numbers & analysis.

  12. Average MPG for gasoline Focus on Fuelly:

    32 mpg average. That's presumably a mix of non-SFE and SFE models, and it's only 1 mpg below the official of the highest-mpg Focus, the SFE.

    There's nothing "sloppy" about my numbers or analysis - it's all based on easily-accessible data.

  13. I'm going to have to agree with Darin. The Prius example is a bad one as well. The 1.5L Prius engine didn't use an external EGR system. When they went to the 1.8L engine they added a cooled external EGR system that can flow up to 30% of the air intake charge as EGR gas. This effectively reduces the displacement of the engine by that same 30% making it capable of being either a 1.8L or a ~1.26L engine. So, it is apples and oranges to compare the two.

  14. Again, the numbers are fairly clear. I understand that some of the current Prius' more modern tech may also help it to get better numbers, but we have a more powerful model which still gets better mpg.

  15. And I would say that the gain in better mpg is largely due to the engine's ability to emulate a smaller engine, not because it actually uses a larger engine.

  16. So, you are saying that "efficiency" of the engine determines the MPG, NOT the size, correct? But if the "efficiency" are the same for two different sized engine in terms of technology and power/liter. Will the smaller engine consume less fuel in a relatively "under powered" application comparing to the same efficient but larger displacement engine?

    The answer is NO.

  17. Well the problem is, people are interchanging engine power efficiency with fuel economy and so things get very confusing depending on what angle you're looking at it from. A turbocharged engine is indeed more efficient because it uses the hot exhaust gases to force in more fuel. However, from the perspective of fuel economy, it's always worse to turbocharge a gasoline engine unless you're turbocharging a small engine in lieu of using a large naturally aspirated engine.

  18. "It's also barely above that of the 33 mpg 2012 Ford Focus SFE sold in the U.S.--with its 2.0-liter engine."

    The US markets only engine choice is a 1.6L Duratec Ti-VCT. with a standard 5sp manual or the optional 6sp Powershift Automatic.

    Other country Markets did however have a 2.0l option on the 5th Generation Fiesta.

    When you "compare" the "real-world" results of the Ecoboost 1.0L Focus, To a (non existing US spec 2.0L fiesta SFE EPA) of "barely above that of 33mpg" (non existant 2012 2.0L fiesta)...

    ^^ Is that not already an efficiency improvement?! Remove 1 cylinder/reducing its displacement of .6L/reducing weight/putting into a larger and little bit heavier Focus package, and average above 33mpg?!

  19. You'll note I was referring to a 2.0-liter *Focus* Michael, not a Fiesta. You've even noted that in the sentences of mine that you quoted (note the word "Focus" in the sentence you quoted...). And as I'm sure you're aware, the Focus uses a 2.0-liter engine.

    And I don't mean to be pedantic, but no market has been offered with a 2.0-liter Fiesta.

    As for your other point, I'm not sure I understand - 34 mpg real-world in the 1.0 is hardly a marked improvement on 33 EPA for the Focus SFE (nor the 32 mpg overall users are getting on Fuelly).

  20. Right, in my haste, i was seeing what i wanted, My appologies. I kept jumping from one thing to another on a similiar topic. I actually made the mistake on that site putting focus instead of fiesta like i did here.

    5th Gen fiesta had 2.0l option before complete rework..

    What i mean by improvement, is that they accomplished similiar performance, from half the engine size. Better Hp/Liter, weight savings, smaller size/less parts/less materials, lower cooling demands, lower costs, probably even higher manufacturing rate.. Though its smaller can perform similiarly as a 2.0l, how is that not improvement?

  21. I'm not sure how you're deducing "lower costs" or "lower cooling demands" - in the case of the Focus, we've gone from a naturally-aspirated 1.6, to a turbocharged 1.0.

    The cost of turning a block of metal into an engine isn't really hugely different whether you're making a 1.0 or 1.6.

    Turbocharging it adds complication and cost - in the UK at least, a 1.0 Focus costs more than the 1.6.

    And as we've discovered, it's not much more economical either. And given the extra complication, would you prefer to have that simple, uncomplicated 1.6 ten years down the line, or the turbocharged tiny engine?

    I've nothing against small engines - quite the opposite - but I firmly believe they have to have some tangible benefits.

  22. Also, why highlight the Fiesta SFE, and not the Fiesta S base/SE/SES models. they all get the same "Combined" EPA rating(33mpg, +/-1mpg city or hiway). Why advocate A higher priced/packaged car, when you can recieve the same perfomance in MPG sence all variants use same engine.

  23. I wasn't highlighting the Fiesta SFE for a start, as you'll see in my response to your comment above.

    But the reason I reference the SFE, is because regardless of combined rating, the SFE has the higher highway rating and therefore is the more efficient car.

  24. One last thought, "your mileage may vary"... But, put in a context where engine size could be the culprit, when it is the driver, who controls the vehicle/fuel consumption. EPA is used for Direct comparison only. and is a Controlled result of what the vehicle is capable of. When Real World is introduced, the EPA figures are thrown out the window and your gas mileage is infinitaly variable

  25. Which is why we use the term "your mileage may vary".

    My point was that the 1.0 varies *excessively* from its quoted figures, to the point where it's barely more efficient than the engine it supposedly replaces (the cheaper, less complicated engine at that).

  26. "EPA is used for Direct comparison only and is a controlled result."

    This is the key point.

    I don't think anyone would argue with an independent audit of a vehicle where a significantly higher-than-usual number of owners claim they can't match their MPG ratings in the "real world". (See recent Hyundai/Kia debacle.)

    But if the official ratings continue to show better economy under repeatable, controlled conditions, then we know the problem isn't the engine, it's the nut behind the wheel.

  27. *Sigh*

    If you can't see that the 1.0 EcoBoost (and other small, supposedly efficient engines like Fiat Twinair) are significantly *less* likely to achieve their claimed economy than a more conventional engine, then that's not a problem of mine.

    I'll say again: The data backs this up. These are engines deliberately designed to test poorly-arranged economy tests, rather than work for real drivers in the real world.

    The ease by which some drivers hit the less optimistic EPA testing is evidence of this - EPA testing is simply a better representation of how drivers drive, compared to the European cycle. But where the 1.0 Ecoboost only gets 70% of its official claims, the average for all new cars in the UK is 88%. Quite a difference, no?

  28. * to *pass* poorly arranged economy tests

  29. "The data backs this up. These are engines deliberately designed to *pass* poorly-arranged economy tests, rather than work for real drivers in the real world"

    Then why would you go onto say...

    "EPA testing is simply a better representation of how drivers drive"

    Even if someone drives "normally" as they do, and whined up at say 31-32mpg combined, They are still within the "EPA estimated 34mpg combined" estimation. They are most likely well within the "City estimate rating" also. That would automatically make me assume, that they drove more city, or idled allot, stop/go conditions, excessive warm-up times, driving without efficient load, etc.

    As we all know EU does have extreme congestion on the streets, geographical speaking

  30. By "poorly arranged economy tests" I was referring more to the European testing - which cars like the Focus 1.0 and the Fiat TwinAir do brilliantly in, yet terribly in the real world.

    EPA testing IS a better representation - and we can expect the Fiesta 1.0 to get more attainable numbers - but we'll have to wait and see what people are able to get in the real world.

    The discrepancy is undoubtedly higher in Europe - city figures always seem even more unattainable over here, and stop-start traffic can really mess up real-world numbers even further (apart from on hybrids, which get better the slower you go!).

  31. This is obvious. If you have to keep revving that smaller displacement engine to get the the same power output to propell the car at certain performance level, then the smaller enginee will consume more fuel to keep up. The downside is also more tear and wear. But it is usually lighter, good for handling

    The larger engine will allow the engine to work at a much lower RPM so it doesn't have to spin as hard.

    When most people compare engines, they only look at the spec power/torque at the peak. They don't look at the power curve and torque curve. They don't look at weight and transmission ratio. All of those impact the MPG significantly.

    Also, didn't Toyota also upgraded the electric motor size when it switched from 1.5/1.6L to 1.8L?

  32. Sorry, but your conclusion couldn't be more wrong. Brake specific fuel consumption (BSFC) maps clearly show that when you have two engines of different sizes loaded to the same amount and geared the same, the smaller one runs more efficiently even though it is 'working harder'.

  33. "when you have two engines of different sizes loaded to the same amount and geared the same,"

    Well, two different sized engine with two completely different torque/power curves is STUPID or STUPID engineering.

    There are so many factors here affecting the efficiency than just size. In general, the "smaller" engines usually have more power per liter than the larger engines. That is why it is more efficient. However, if the engine is significantly smaller, and it has to stay at higher rpm to get the same amount of power, then it is NOT going to be more efficient. Many of the 600CC motorcycle engine will easily crank 120HP at 8,000 RPM but have terrible power curve. Dropping it into Econ box to replace the 1.x liter engine will NOT work.

  34. Find me a similar designed engine with everything else being the same, VVTI, Turbo chargin, direct injection...etc And make sure they have the same Power/Liter but with two different engine size, and put it in the EXACT same load condition and see if they consume the same amount of fuel.

  35. Explain to me: "Brake specific fuel consumption (BSFC) maps clearly show that when you have two engines of different sizes loaded to the same amount and geared the same, the smaller one runs more efficiently even though it is 'working harder'. "

    How can you have two different "power output" engine geared to be the same and operate with the same load to spin at the same RPM?

    Is that even a technical statement?

    Engines have different optmum operating point. Is that load geared for the smaller engine or the larger engine? If the smaller engine has to scream near the redline to produce the same power as the larger engine at much lower RPM for the same given load, will the smaller engine still be efficient?

  36. If you have two engines of different displacements connected to the same drivetrain putting out the same amount of power, its obvious that the smaller engine is going to be at a higher percentage of maximum load. When you look at BSFC charts you can see that an engine that is running at a higher percentage of maximum load will return greater efficiency. So, all things being the same, a smaller engine will return greater efficiency.

  37. "If you have two engines of different displacements connected to the same drivetrain putting out the same amount of power,"

    You already discounted the efficiency of the larger displacement by saying that "putting out the same amount of power". So smaller displacement with same power as larger displacement is more efficiency.

    So, they are NOT the same engine. Like I said, find two engines with the same HP/Litter and then re-run your BSFC test and see what happens, especially at a constant load.

    The smaller displacement will save fuel when it is "idle" situation.

  38. I'm sorry you don't seem to understand. By saying they put out the same amount of power it is like saying you have the same car with two different engines in a real world situation. For example, for a car to go 55 mph you might need 15 horsepower to maintain that speed. If you put a 1.5L engine in that car it is going to be loaded to say 40% of its maximum output. If you put a 2.0L engine in the car with the same drivetrain (gearing), the engine is only going to be at say 30% of its maxmimum output. If you look at a BSFC map and look at any engine it is going to be more efficient at 40% load than 30% load. That is why smaller engines return better efficiency.

  39. 1 question, will this "observation" change in the case of a "series-hybrid"? I know that we don't have too much samples at this point. But theoritically speaking, in the series-hybrid case, it is heavily depending the battery size and driving mode (long hill climb vs. hwy cruise vs. city driving)...

  40. I suppose again it's affected by several factors. Some series hybrids may be better suited to a certain type of driving than others. A smaller engine may not necessarily hamper them even in harder acceleration etc, if the electric motor is powerful enough to compensate, and the battery has enough juice to provide power for longer.

  41. Instead of arguing over the "size", we should have argued that the most efficient engine with the power curves fits the BEST for intended application (vehicle size, gearing ratio and performance expectation) will produce the best MPG regardless of size of the displacement.

  42. Very good point Xiaolong. I tried to imply this in the last few paragraphs, but perhaps I should have made it clearer.

  43. Of course, there are vehicles that show the more traditional relationship between engine size and MPG. Look at the Toyota Tacoma
    L4 versus V6
    2012 21.1 18.0
    2011 21.0 18.4
    2010 22.0 18.1

    The four banger is consistently better. I am not sure why that relationship works here but not so much with the F-150.

  44. I think the F150 proves the point that if you put a more powerfull engine in a vehicle, the driver will use the power, and reduce the mpg. I want to see the average accelleration, and speed of the v6 vs v8. *** V6 is more powerfull over all.

  45. The real way to improve fuel economy is not a smaller engine, but a different combustion cycle. OTTO cycle is the boring regular combustion cycle. Good performance, so-so efficiency.
    Atkinson is a good step in more efficiency but less HP for the same displacement. Works well in conjunction with electric motors to have enough acceleration. An engine that could switch from Atkinson to OTTO and back on demand would be great, then the engine could be in non-hybrid cars.
    HCCI/lean burn is even better. Honda had lean-burn years ago but couldn't figure out the emissions so they stopped making them.
    Lean burn is the way for great fuel economy. Toyota may make a lean burning engine for the 2015 Prius.

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