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I've been searching for some cars on the internet and I've observed that newer cars get smaller engines.

For instances, I've found a Ford Focus diesel 1.6, or even a Mercedess A Klass 2015 diesel has a 1.6 engine, which seem to be both good.

Could you explain why?

  • Today I am driving a 2015 Ford Fiesta with a 1 litre 'Ecoboost' engine. It is extraordinarily punchy for it size. – Gusdor Sep 14 '16 at 12:46
  • The Mercedes 1.6L Diesel is also used in the V-Class (Vito) Transporter and works incredibly well in there... – AnyOneElse Sep 14 '16 at 14:28
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    Because you can get lower emissions in a test environment using smaller engines in their most efficient load range. In actual road use, then, it's completely irrelevant how inefficient they may be when they run on higher loads. - Well, at least that's what I think, when I see a 1 litre turbocharged engine with over 100 hp... ;) – Alexander Kosubek Sep 15 '16 at 7:01
  • Money. "In fact, gas had gotten really cheap [in 1998] by historical standards allowing people to buy gas guzzlers like SUV’s and Hummers." –Inflation Adjusted Gasoline Prices. You may as well have asked why we used to (?) have such unnecessarily large automobiles; same answer ;) – Mazura Sep 16 '16 at 3:19
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Smaller engines provide a myriad of benefits versus huge engines. Mainly it's fuel efficiency which also translates into emissions. The less fuel you burn, the fewer amount of gasses that get expelled from the engine. Not only that, but weight is something to consider as well. Space in the engine bay for more accessories is also something the engineers enjoy about it as well.

You don't need huge 8 cylinder engines in regular cars anymore because engineering has come to a point where a 1.4L can push a huge car. It's all about engine design. You won't get the torque you would out of 6 or 8 cylinders, but for a daily driver that gets you from point A to point B; That's all you really need. Additionally, with the ever growing implementation of forced induction (Turbos and superchargers) becoming normal, horsepower and torque is more easily achieved in much smaller engines. I've seen little 2.0L that push 275HP stock out of the factory, which would be near impossible had a turbo not been used.

Mainly though it has to do with fuel consumption and emissions. As a side note, I don't mind it either; It's much easier for technicians to work on.

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    Less cylinders = less problems! – Brian Knoblauch Sep 14 '16 at 12:45
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    "Parts you don't have can't break" - Henry Ford – anonymous2 Sep 14 '16 at 12:57
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    @MasonWheeler, the place I found it is in "Two-Stroke Engine Repair and Maintenance" by Paul Dempsey, Publisher: McGraw-Hill Companies, ISBN 978-0-07-162539-5, p. 23. – anonymous2 Sep 14 '16 at 14:09
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    Regarding the Ford quote, in Lee Iacoca's autobiography I remember him mentioning that the K-class cars replaced a three-part heater box with a two-part box, arguing that two parts are less likely to break than three parts. This was sometime in the mid-to-late eighties I think. – dotancohen Sep 14 '16 at 14:19
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    Actually, fuel efficiency drops with engine size-to-hp ratio. The reason of then vs now is that technology went so much forward that efficiency gains from other sources outpaced efficiency loses from shrinking the engine. When you look at Prius engine, it's quite huge for it's power compared to contemporary engines: 1.5l and only 75hp. Another version of this engine, but tuned for less efficiency and solo operation does 106hp. Smaller engine is simply cheaper, that reason alone beats all others. Look at ship engines, they only grow bigger pursuing efficiency. – Agent_L Sep 15 '16 at 7:44
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As cloudnyn3 says, it's all about improvements in engine design - a modern 1.4 can produce just as much power as a 2.0 from 20 years ago, but with much better fuel consumption and emissions - plus it's smaller and lighter, which helps again - you get more space in the car for other things, and the better fuel economy means you can fit a smaller fuel tank without losing range, again gaining space.

  • With regards to design, the advances in things such as prototyping and computer modeling specifically help here. Plus computer assisted manufacturing techniques allow for smaller and smaller tolerances too. – Steve Matthews Sep 14 '16 at 14:52
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There has been a trend with the development of internal combustion engines (ICE) since their inception to make them smaller, lighter, cheaper, more powerful, and more efficient since they were invented.

Early ICE were extremely large, yet produced very little power when compared to modern engines. The first automobiles had to be made extremely large, and robust enough just to house these engines. In the early days, automobiles were also very expensive, and the average person would have not been able to afford them.

In October 1913, Louis Coatalen, chief engineer of the Sunbeam Motor Car Company entered a V12 powered car in the Brooklands short and long handicap races. The engine displaced 9 L (550 cu in), with bore and stroke of 80 x 150 mm. An aluminum crankcase carried two blocks of three cylinders each along each side, with a 60 degree included angle. The cylinders were of iron, with integral cylinder heads with L-shaped combustion chambers. Inlet and exhaust valves were operated by a central camshaft in the V. Valve clearance was set by grinding the relevant parts, the engine lacking any easy means of adjustment. This pointed to Coatalen's ultimate aim of using the new V12 as an aero engine, where any adjustment method that could go wrong in flight was to be avoided. As initially built, the V12 was rated at 200 bhp (150 kW) at 2,400 rpm, weighing about 750 pounds (340 kg). The engine powered the car (named ‘Toodles V' (for Coatalen's wife Olive's pet name) to several records in 1913 and 1914.

https://en.wikipedia.org/wiki/V12_engine#Motor_car_engines

The 'Toodles V' engine was much larger and heavier than a modern engine, but despite that fact, it only produced as much power as a comparatively tiny modern engine. Early engineers simply lacked the ability to make the engines smaller, and lighter at that time.

Henry Ford helped change this drastically. He introduced a very light, and small 4 cylinder engine for the Model T. His engine only produced around 20 horsepower, but that was enough for the average person. There were still large, and powerful engines produced for the auto enthusiasts, but it did create a market for an affordable car.

Over the next several decades, engine designs steadily improved which led to the muscle car era. Auto racing became much more popular and mainstream, and car companies competed with each other to produce more powerful engines. There is an old adage that goes something like "Win on Sunday, sell on Monday". At this time, manufacturers had very few regulations on the types of the cars they could produce. The cars were basically death traps, and the manufacturers knew it, and chose to do nothing. Many of them lacked any basic safety features such as seat belts. There was also very little regard for fuel economy. Gas was cheap, and there weren't regulations on emissions, and fuel efficiency like there is today.

Beginning in the late 1960s, the government sought to limit emissions from automobiles. This led to the creation of the EPA in 1970. The gas shortage in 1973, and the subsequent rise of the cost of gas were also driving factors which marked the end of the muscle car era beginning with the model year 1974.

For the first time, manufacturers were mandated to meet the strict guidelines created by the US government for fuel economy and emissions. The problem was that manufacturers had no idea how to meet the new strict regulations, and were not given much time to comply. These new emissions rules forced manufacturers to add emission control devices such as catalytic converters, which reduced the flow of exhaust gasses. EPA regulations also had the lead additive removed from gasoline in 1973, which forced engine designs to change so they can handle unleaded gasoline.

In the mid 1970s, there were many cars made which had large 8 cylinder engines that only produced around 100 horsepower. The 1971 Corvette was offered with an engine that had 425 hp, and in 1975 it only had 205 hp. The base 1975 model was even worse which only had 165 hp, which is about the same power that a family minivan has today. This led to a large public outcry, and car manufacturers tried in vain to make improvements, but improvements came very slowly. It wasn't until the late 1990s when Corvettes had similar performance numbers to their muscle car predecessors.

Around this time, small and efficient cars from Japan were being introduced to US markets, and were well received. This eventually led to the loss of dominance for US auto manufacturers in the United States. US companies were forced to get into the compact car market because they were losing sales to imports. Prior to that, very few foreign cars were sold in the US. Many of those sales were for small European sports cars such as Triumph, Alfa Romeo, MGB, Austin-Healey, Jaguar, Porsche, Mercedes-Benz, Lotus, etc.

Over time, technologies such as electronic fuel injection, and turbo charging led to significant improvements in efficiency, and power. Many modern engines can deliver a large amount of horsepower, but still sip fuel. These new designs are so efficient, that it is no longer necessary to have a large engine in most cars.

Car manufacturers are still being pressured to produce even more fuel efficient vehicles. There are also regulations which limit the average fuel consumption across their entire fleet. They are basically forced to produce either all electric, or hybrid cars to get the average MPG down to the standard. There are still cars with big V8s, and V10s, but the reason why there are being less produced, is because of strict regulations.

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This comes down to efficiency.

Not too long ago, cars were bigger and heavier in general. The EPA and other government organizations in countries that produce cars mandated higher fuel efficiency. This pushed R&D in two areas:

  • Making vehicles weigh less, so the engine needs less energy to move the car.
  • Making engines produce more power with less fuel used.

The first item is off-topic for this question, but vehicles have become lighter for several reasons. The basic physics is that regardless of the powertrain, a vehicle with a certain mass requires a minimum amount of energy to move. Lower that mass, it needs less energy (read: fuel).

Engines have become far more power and fuel efficient in recent years. Let us put some concrete numbers on this with some examples. I will pick a truck that I am familiar with and have researched previously.

A third generation Chevy Silverado (2014+) comes with two primary engine options:

  • 4.3L V6 - 285HP
  • 5.3L V8 - 355HP

If you go back a few years to the second generation Silverado (2007-2013), there are a few more options over the years but here are some of the more widely produced engines:

  • 4.3L V6 - 195HP
  • 4.8L V8 - 295-302HP
  • 5.3L V8 - 315HP

That is a single generation/iteration of vehicle, and the power is quite different. The newer V6 produces almost as much HP as the previous V8, off by 10HP. It produces 90HP more than the previous V6 with the same displacement.

GM put its LFX engine in quite a few vehicles in the 2015 and 2016 model years. Its power varies based on what vehicle it is in (there is more to an engine than the metal block, there are many parts which impact power). In general, they vary between 301 and 323 HP. This 3.6L V6 has more power than the previous generation V8 listed above! In fact the 3.6L LFX engine has 15-35 more HP than the current-generation 4.3L in the Silverado (but less torque).

Without making this answer too long, you will find very similar results if you look at other manufacturers and engines (I4 v V6). Across the board, there is a tremendous amount of pressure to improve engine efficiency.

Modern engines basically have an extra two cylinders compared to engines produced only ten years ago. Smaller displacement generally means greater fuel efficiency, and modern designs also produce more power.

Newer cars have smaller engines because that new I4 engine can produce as much power as the last car generation's V6, and use less fuel doing so. This satisfies the EPA, as well as drivers who spend less on fuel yet still have plenty of power when needed.

(Note: I omitted some of the engine options above which are not very common and don't really add much to the discussion. Yes, I know GM offers a 6.2L V8, but very few Silverados have it and it doesn't help answer the question)

  • Getting more HP out of liter of displacement is efficacy. Efficiency is getting more miles per galon. – Agent_L Sep 15 '16 at 14:42
  • More miles per gallon is "fuel efficiency." More power per unit of displacement is "power efficiency" or whatever you want to call it. Efficacy is the ability to get a result. One could argue that as long as the engine has enough torque to move the wheels from a dead stop, it is efficacious. – user4896 Sep 15 '16 at 17:10
  • Efficacy is actually used physical term and it's quantitative. Yes, it's confused with efficiency all the time. Even if we call them both by descriptive terms, you still mixed then up in your answer. Larger, slower running engines are more fuel efficient but less power efficient and the shrinking trend was enabled by technological progress that increased them both. – Agent_L Sep 16 '16 at 13:46
  • ...so you are saying engines have become more fuel efficient while delivering more power per unit of displacement, which is the conclusion I came to. – user4896 Sep 16 '16 at 14:23
  • No, I said they've become more fuel efficient despite delivering more power per unit of displacement. – Agent_L Sep 16 '16 at 14:31
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Because a piston-powered internal combustion engine is a non-continuous power source which only produces power when the fuel in the cylinder goes "bang" there are two basic ways to get more power out of an engine: 1) make it spin faster, giving more bangs per unit time, or 2) keep it spinning slower, but add more cylinders to get more bangs per unit time.

(Yes, you can add superchargers or turbochargers or some other system to pack more fuel and air into the cylinder, and you can pack multiple sets of points into the distributor and rotate the distributor more slowly - but let's ignore those things right now, just for the sake of argument :-).

Back In The Day (tm) most gasoline engines used the points-and-rotor ignition system, where a spring-driven mechanical switch (the "points") was opened and closed by a cam on the distributor shaft, generating a spark which was routed to the appropriate cylinder by the rotor and the wires between the distributor and the spark plugs. The mechanical switch generated a spark by interrupting electrical current flow through the coil when the switch opened; the current flowing through the coil caused a magnetic field to be formed, and interruption of the current flow caused the magnetic field to collapse which caused an induced current in the iron rod in the middle of the coil which was connected to the center pole on the distributor.

Because the points are a spring-driven mechanical switch they have a limit on how fast they can react. Generally (and I'm being very general here) engines using an ignition system with points in them wouldn't run reliably at speeds above 2500 RPM because the points would "float" in the open position - and because the points didn't close no current could flow through the coil to set up the magnetic field which would collapse when the points opened to generate the ignition spark. Yes, you could use a stronger spring on the points but this caused unwanted problems like excessive wear in the distributor. So with an absolute(ish) upper limit on RPM the only way to get more power out of an engine was to add more cylinders to it so you got more bangs out of the engine for each rotation. A four cylinder engine gives you two bangs per rotation; six cylinders, three bangs; eight cylinders, four bangs. Huge aircraft engines with up to 22 cylinders gave even more bangs per rotation. So, more cylinders, more power.

Enter the world of electronic ignition, which is now standard on almost every gasoline engine in the world. This system does away with the mechanical switch, replacing it with an all-electronic device with effectively no "reset" time, which allows engines to be run much faster. It's common today to run four-cylinder engines above 3000 RPM at highway speeds - the little four-banger in my Ford Fiesta turns at around 3200 RPM at 65 MPH. At the same time, manufacturers have made incremental improvements in engine design which contribute to more horsepower per unit displacement. But IMO the biggest contributor to higher horsepower from smaller engines has been electronic ignition, which allows a small engine to operate at higher RPMs.

YMMV :-)

  • I argue that electronic injection has more impact than ignition timing. – JimmyB Sep 14 '16 at 20:27
  • The most simple way to get more air/fuel into a cylinder: Bigger cylinder, i.e. more displacement. No need for turbochargers or extra cylinders. – JimmyB Sep 14 '16 at 20:30
  • @JimmyB Politely disagree - going from points to electronic ignition was a huge upgrade for my old holden6. – Criggie Sep 15 '16 at 7:53
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Different answers touch on different parts of the overall answer. The root answer you're looking for is power density: how many horsepower (kW, whatever) per cubic inch (or liter) of displacement.

How much power does it take to push this vehicle around in a desirable fashion? A significant fraction of a vehicle's weight is the engine, so a smaller, lighter engine will mean less weight to push around. And less mass = less gas. This is why Ford's current F-150 line uses an aluminum body, instead of a steel one. It's lighter, requiring less power to move it.

As @Bob Jarvis points out, electronic ignition, as opposed to the old points/coil/distributor system, provides the ability to run high revs and still maintain ignition timing. Indeed, it provides more precise timing across the entire range. And more precise timing results in higher power density.

Fuel injection provides for a much more precise mixture of fuel. With this, and more precise timing, you can use higher compression ratios (8:1 for the carbureted 1981 Omni I drove as a teenager, 9.5:1 for the fuel-injected 1998 Dakota I drove more recently; using the same cheap, unleaded gasoline). Higher compression ratios allow for higher power density, as well as higher thermal efficiency.

Gasoline Direct Injection can further boost the compression ratio you can use. Gasoline is injected directly into the cylinder, cooling just the air in the cylinder. Port injection sprays into the intake manifold, cooling down the intake valves and the manifold in the process. Cooler air can handle more compression before it starts to cause auto-ignition (knock).

Turbos and superchargers allow you to squeeze a greater volume of air (and fuel) into a given displacement, allowing your engine to perform like it has much more displacement. It will burn more fuel when doing so. This provides "on demand" power. It can push your "on demand" power density really high; high enough that more cylinders or displacement aren't needed to achieve a desirable level of power. You don't want to run at that throttle setting all the time, but it's there when you need it.

Variable valve timing allows you to do Atkinson/Miller Cycle instead of plain Otto Cycle. This doesn't help your power density so much as it further divides your "base" power density from your "on demand" power density. If you aren't demanding power as often, this will further boost your fuel economy. But it can revert back to full Otto Cycle, getting you back to your max "on demand" power setting when needed.

The end result is that all of these little tricks can squeeze more power out of each cubic inch (liter) of displacement. And provide you a greater range of power settings, with the lower power settings providing significantly less fuel consumption (and significantly lower emissions) per mile (or km, if you prefer).

Ford's Ecoboost line of engines uses all of the above. They're rapidly replacing V8s with V6s and replacing V6s with I4s, as a result. @Gusdor mentions a 1 liter engine in his Fiesta; pretty sure that's a 3-cylinder Ecoboost engine. Whether or not the resulting engines are as reliable, long-term, is an open question. Turbos, particularly on high-revving gasoline (petrol) engines, tended not to be so reliable in the past. Those engines are new enough that there's not much long-term data on them, yet. It's possible they've got the issues beat. Just too soon to tell.

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A few years back, the thing that was all the rave was muscle cars. Rapid acceleration, loud engines, and power were all the style. However, over the years, the EPA and other various agencies have been pushing for less emissions (save the environment). Consequently, auto manufacturers have started building cars with the goal of having minimum carbon monoxide, nitrogen oxides, and hydrocarbons. Evidently, the smaller the engine, the less emissions.

Furthermore, the fad of muscle cars has, to a large extent, given place to the mode of luxury vehicles, which can be designed with smaller motors but more features. So the clients are happy, the manufacturers are happy, the EPA is ~happy, and, as cloudnyn3 said, the mechanics are also happy.

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It actually may be the case that this trend will reverse. Small engines need to operate at wide open throttle (WOT) to produce any useful amounts of power, and WOT enrichment will reduce fuel efficiency, something that is not measured by current unrealistic driving cycles. Techniques such as gasoline direct injection mean particulates are produced, and a particulate filter costs a lot (but lung cancer costs more for those affected). A turbocharger is a fragile component and may be overall burden during the entire lifetime of a car, including its last years. Also improvements in engine operating cycles (Atkinson cycle) mean that the volumetric efficiency may actually decrease although energy efficiency will increase. Atkinson cycle was originally used in hybrids, but due to wide variable valve timing technology Atkinson cycle is finding use in non-hybrids as well.

For example, consider my 1989 Opel Vectra. 115hp 2.0 litre C20NE engine. Now consider the modern equivalent: a Toyota Prius. 1.8 litre 2ZR-FXE engine with 98 hp output, although the electric boost produces some additional amounts of power, so overall those cars are about equally powerful and accelerate about equally fast. From 2.0 litres to 1.8 litres is not much of a change.

Yes, there was a trend to downsize and to turbocharge, but the trend seems to be reversing. For example, Toyota Yaris that used to have 1.33 litre naturally aspirated engine is moving to a 1.5 litre engine in its non-hybrid configuration in the European marketplace; the hybrid always used a 1.5 litre engine (slightly different from the 1.5 litre non-hybrid). I also understand that 1.5 litre engine was offered in the North American marketplace all the time.

So, don't make a final conclusion before electric cars will eventually replace liquid fuel powered cars. It may be the case that the last liquid fuel powered cars running on dead dinosaurs(*) will use Atkinson cycle engines without turbocharging, meaning the size of the engine is about the same as it used to be in old cars.

Me? I moved from 2.0 litre (1989 Opel Vectra) via 1.33 litre (2011 Toyota Yaris) to 2.5 litre (2016 Toyota RAV4 hybrid), although at the same time I moved slightly upwards considering the car size, price, weight and performance as well.

(*): Yes, I know petroleum actually doesn't come from dead dinosaurs...

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