The most common engines on modern cars are in-line and V-shaped. Boxer engines are used much less frequently, mainly on Porsche and Subaru models. What is the reason for such inattention, and what advantages does a boxer engine have?
Design options
This motor differs from its counterparts in that the cylinders in it are not located vertically or at an angle, but horizontally, i.e. in opposite directions from each other. Hence the name - boxer or horizontally opposed engine.
There are two options for the design of such motors. The first is that the pistons move towards each other and have a common combustion chamber. Their advantages include the high quality of gas exchange, a simpler design compared to in-line or V-shaped motors. Similar devices were used on military equipment, in particular, on Soviet T-64 tanks, which could run on different types of fuel: kerosene, gasoline, diesel fuel. To transfer the tank to another type, it was enough to move the special lever to and set the required ignition angle. The engine was equipped with two turbines: pressurization, which increased power, and gas, which brought the exhaust gases out. The disadvantages of such opponents are the same as those of two-stroke engines: higher fuel losses through To this, as you might guess, decent dimensions are added, because two crankshafts are required for pistons moving towards. The second option is more common. This is what we most often mean when we mean a boxer engine. Relatively speaking, this is a V-shaped motor, the cylinders of which they decided to decompose at an angle of 180 degrees. It is used on cars (Porsche, Audi, Subaru) and motorcycles (Dnepr, Ural). We will talk about it below.
Advantages and disadvantages
So, the benefits. The main advantage of this engine layout is a lower center of gravity, which improves vehicle handling. Also, the opponent compares favorably in terms of size and weight. It is noticeably shorter and lower than inline engines. Another advantage is the excellent balance, which is ensured by the arrangement of the pistons, which neutralize each other's vibration. The shift in the center of gravity of the power unit to the center of the car makes it possible to make the turn more accurate and stable. This is especially important for sports models, where handling is not just in the first place, but in the very first place. There are also advantages in frontal collisions. Since the boxer engine is located low, it will move under the cab in the event of a collision, and not into the passenger compartment. So the presence of such a motor speaks in favor of the safety of the machine.
Does a boxer engine have disadvantages? Yes, and quite significant. It was they who became the reason that such motors were not widely used. Opposites are short and tall, but they are much wider than engines where the cylinders are in a row or in the form of a V. This creates a lot of problems for designers. The engine compartment must be such that the boxer engine fits into it in width. In this case, it is necessary to compactly arrange the steering and steered wheels. Another problem is the availability of nodes for maintenance. If the engine oil can still be changed independently, then only a specialist can perform the rest of the operations. It is not recommended to even change the spark plugs in the engine yourself, because you can easily damage the cylinder head. These shortcomings make boxer engines more expensive to manufacture and maintain. And this, in turn, affects the price of the car.
As you can see, this type of device has both advantages and disadvantages. However, their competitors are also imperfect. Therefore, when choosing a car, decide whether the complexity and high cost of maintaining the power unit is so important to you. It is quite possible that the good handling of the car will more than pay for these costs.
Modern reciprocating internal combustion engines (ICE) can be classified based on criteria such as the type of fuel consumed and the arrangement of the cylinders. If with the division of engines based on the type of fuel, everything is more or less clear even to people who are very far from technology, then with the division according to the arrangement of cylinders, everything is not so obvious. In this material, we will consider one of the types of internal combustion engines with an unusual arrangement of cylinders, namely a boxer engine. Here you will learn about what a boxer engine is, how it works, what its pros and cons are and where it is used.
The design and features of the boxer engine
Scheme of operation of a boxer engine
Opposed internal combustion engines are those whose cylinder camber angle is 180 °. The pistons in them move in a horizontal plane, and mirror each other. This means that they reach their highest point at the same time. By the way, this is precisely one of the main differences between boxer power units and the more common V-shaped ones: in them, the movement of the pistons is carried out synchronously (when one of them is at the top point, the second is located at the bottom).
Due to this arrangement of cylinders, boxer engines have a low center of gravity. In addition, their height is significantly less than that of the V-shaped ones, they are more “flat” and take up less space in the engine compartment. One of the distinguishing features of boxer engines is the presence of two gas distribution mechanisms (they, like the V-shaped ones, most often have one crankshaft). As for the principle of operation of these motors, it is exactly the same as that of all other internal combustion engines: the movement of the pistons that drive the crankshaft is carried out due to the pressure of the gases formed during the combustion of the fuel mixture.
Types of boxer engines
To date, there are three main types of boxer engines:
- boxer;
- OPOC;
- 5 TDF.
They differ from each other mainly in the way in which the pistons move in them.
boxer. In boxer engines of this type, each piston is located in its own cylinder, and they are located at a certain distance from each other, which always remains constant. This is precisely the main feature of such power units. Since in the process of functioning the movement of their pistons resembles the movements of boxers in the ring, they received the name Boxer.
OPOC. This abbreviation stands for Opposed Piston Opposed Cylinder, and the design feature of boxer engines of this type is that they have two pistons in each of the cylinders. They move towards each other. OPOC boxer engines are 2-stroke and do not have cylinder heads or valve trains. Thanks to this design, these power units are lightweight, and they are both gasoline and diesel.
5 TDF. This type of boxer engine is a domestic development. At one time it was created specifically for installation on T-64 tanks, a little later it was used in the T-72. Just like in the OPOC boxer engine, its cylinders contain two pistons that move towards each other, but unlike it, each of them has its own crankshaft. Combustion chambers in 5 TDF boxer engines are located between the pistons, they operate on both gasoline and diesel fuel. Now these power units are no longer produced.
Pros and cons of boxer engines
Crankshaft and pistons of a boxer engine
Like other types of internal combustion engines, boxer powertrains have both pros and cons. As for the advantages, one of the most significant of them is a very low level of vibration during operation. These motors owe this precisely to the opposite arrangement of their pistons. The fact is that when moving, they mutually balance each other, and the imbalance of forces that leads to vibrations is almost completely absent.
This advantage of boxer engines entails another significant plus: since there are practically no vibrations, the wear of moving parts is much slower than in, say, V-engines. Accordingly, the resource of such motors is very large: practice shows that their mileage before overhaul is about half a million kilometers. Some owners of cars with boxer engines claim that this figure is even higher in practice, ranging from 600,000 to 700,000 kilometers.
Another plus of this type of power units is the low center of gravity. That is why they are often installed on sports cars. When cornering at high speeds, boxer engines provide increased stability of the machines. In addition, as mentioned above, the advantage of motors of this type can be considered their small height. In fairness, it should be noted that at the same time they are somewhat wider than power units of other types (for example, the same V-shaped motors).
As for the disadvantages of boxer engines, the main ones are the following: high cost and difficulty in repair. The design of such motors implies high manufacturing accuracy of many of their main elements, the use of expensive high-strength materials. In addition, their assembly and adjustment is much more complicated than similar procedures for V-shaped or in-line internal combustion engines. Diagnosis and troubleshooting of boxer engines is possible only with specialized equipment and specially trained personnel. It goes without saying that even a minor repair of such motors costs a lot for the owners of the cars on which they are installed.
Also, a significant disadvantage of boxer engines is a significant oil consumption. However, in terms of such an indicator as fuel consumption, they are still inferior to modern V-shaped and in-line power units.
Scope of boxer engines
Boxer engines are not as widely used as V-twins and in-line engines, but there is an automaker that has been installing this type of engine in its cars for half a century. This is the famous Japanese company Subaru. In addition, boxer units can be found on some models of Volkswagen and Porsche, they were once equipped with Soviet motorcycles "Ural" and "Dnepr", Hungarian buses "Ikarus".
It should be noted that in recent years, interest in power units of this type has increased significantly. According to some reports, research and development to improve the OPOC boxer engines, conducted by a group of American engineers, is funded by Bill Gates.
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Such a power unit as a boxer engine (in particular, the manufacturer Subaru) is similar in principle to a standard, in-line internal combustion engine. What distinguishes it is the specificity of the location of the pistons, cylinders, due to the horizontal (and not the usual vertical) installation of the engine. Therefore, the pistons of the boxer engine are located horizontally, moreover, opposite (opposite) to each other, in pairs. Also, each of these pairs of engine pistons has a pair of camshafts.
At first glance, Subaru's boxer engine is more compact than others of the same power and volume. This illusion is created because it is "flat", evenly fills the engine compartment. At the same time, the motor-plate is short, flat, but wide. Its design is represented by semi-blocks of two cylinders, but in width, in addition to the crankcase with a pallet, like an in-line one, there is also a semi-block and a head.
The first Subaru boxer internal combustion engines were noticed and installed on sports cars by racers. Under them, 12-cylinder engines were later developed, instead of the 6-cylinder ones used. 
Benefits of a Subaru boxer engine
Subaru's boxer engine has many advantages:
- The distribution of mass is symmetrical around the axle, not specifically on it (less load on the rear wheels) - due to the low center of gravity (plus the possibility of its displacement).
- High functionality, a relatively long duration of work until the first need for repair is the most important plus and argument for installing a Subaru boxer engine.
- Minimization (or complete absence of vibration), which, when installing a conventional engine, creates considerable discomfort for the driver / passenger.
The first plus (dignity) is most appreciated by the owners of sports cars. Because, at high-speed turns, the Subaru boxer engine will give more sustainability. In addition, the speed indicators for cars using these particular engines are relatively better than similar ones (especially among 12-cylinder ones).
The second advantage is engine longevity– has been extensively checked/confirmed. Until the need for a major overhaul, the boxer engine will please the car owner with more than one thousand kilometers traveled without problems.
The last (third advantage) is possible, among other things, due to the horizontal arrangement of the pistons working against each other, creating a certain balance, counterweight. Not all models of Subaru boxer engines, unfortunately, can boast maximum vibration resistance. The best way to "resist" vibration loads is a six-cylinder boxer engine (similar to a 6-cylinder variation of an in-line engine). But already the 4-cylinder does not have such successes and significant advantages. 
Subaru boxer engine cons
However, in every advantage of Subaru's boxer engine, you can find a small fly in the ointment. Of these shortcomings:
- The high cost of engine maintenance, the difficulty in selecting the necessary spare parts. And, among other things, it is advisable to trust only professionals who specialize in this in matters of repair of these particular engines.
- The high cost of Subaru's own boxer engine, explained by the complexity of the design.
- Also, a large oil consumption is added to the consumable items using such an engine.
Self-repair of a boxer engine is also impossible due to the need for a specialized tool, without which many parts of a non-standard, horizontally located engine cannot be reached.
The spectrum of use of the Subaru boxer engine
The slightly difficult financial situation of a significant mass of motorists does not allow the popularity of Subaru boxer engines to spread. Their application is most widely used in the field of racing, high-speed car models. Because here, the previously mentioned advantages of Subaru boxer engines are much more important and cover the disadvantages of their use.
In addition, they are installed, of course, in Subaru car models. Also, Porsche often resorts to installing these particular engines in their cars.
The boxer engine is a form of the device of the internal combustion engine of a car, which has a special structure: its pistons are located at a developed angle and move in a horizontal plane towards each other and in the opposite direction (from each other). Another, adjacent pair of pistons, is located in the same position (for example, at the top).
The interaction of the pistons inside the engine is somewhat reminiscent of a boxing round, hence the other name of the device - a boxer. The design of the mechanism involves the installation of each piston on separate crankshaft journals. The number of cylinders in a boxer engine can be from 2 to 12, but always even. The most popular devices are with four and six cylinders (four- and six-cylinder boxers).
There are many brands of cars on the modern automotive market, each of which adheres to its own concept of car equipment. Two firms are now engaged in the development and use of boxer engines: Subaru and Porsche. Previously, the boxer engine was installed on cars such as Alfa Romeo, Honda, Chevrolet, Volkswagen, Ferrari and others.
The first boxer diesel engine was launched by Subaru in 2008. This is a four-cylinder boxer with a capacity of 2 liters, capable of developing power up to 150 hp. During its development, the Common Rail system is used.
Some models of Porsche cars use six-cylinder engines (Cayman, 911). For sports cars, high-power eight- and twelve-cylinder boxer engines have been developed. Many professionals say that only six-cylinder boxers differ from the operation of conventional engines, four- and two-cylinder ones are almost the same.
Boxer boxer - basic principles of work
In general, the operation of a boxer boxer is similar to the operation of other internal combustion engines. The main distinguishing feature of its device is the arrangement of the cylinders. The cylinders in it are mounted horizontally, unlike most engines. This also establishes another movement of the pistons: not up and down, but from right to left and vice versa (from one edge of the cylinder to the opposite).
The original development of the horizontal boxer was not Subaru's, as many tend to think. Motors of this type have already been used previously on Ikarus passenger buses, as well as on motorcycles (both domestic "Dnepr, MT" and foreign-made "enduro-tourist BMW R1200GS and others"). In addition, such engines have long been used in military vehicles, in particular, in domestic tanks.
Naturally, such an engine structure has its pros and cons. Let's consider them in more detail.
Benefits of the Boxer Boxer
Pictured is a Porsche boxer engine
The main advantages of an engine with horizontally arranged cylinders include:
- Helps to shift the center of gravity. The weight is distributed around the axle, which can significantly improve the handling of the machine. For many, this factor is decisive when choosing an engine and a car, this is especially true for Russian roads.
- No vibration during operation. Engines with a standard structure and vertically arranged cylinders vibrate during operation, transmitting waves to the entire structure, which is not very comfortable for the driver.
- Long work. The resource of the boxer boxer installed in Subaru is so great that it allows the car to be operated for a long time (it lasts for more than a million kilometers).
Disadvantages of a boxer engine
Pictured boxer engine Subaru Outback 2015
Despite the significant advantages, an engine of this type has significant drawbacks that the developers have not yet gotten rid of:
- Requires expensive maintenance. Often, conventional engines are repaired on their own or in car dealerships for a small amount. However, in the case of an opposing boxer, this is not possible. Its design is too complicated, so it is better to entrust the installation to professionals. Moreover, you will have to pay a decent amount of money for such services.
- The second drawback follows from the first - even with sufficient funds to maintain this type of engine, it may be difficult to find a qualified specialist who can provide quality service.
- The complexity of the boxer device contributes to an increase in the cost of its components, which creates additional costs for repairs.
- Increased consumption of automotive oil. A conventional engine consumes no more than three hundred grams of oil during its operation, and a boxer engine consumes much more.
Subaru has no intention of swapping boxer engines for standard ones, as they tend to think that would be a big step backwards. The high cost of engine maintenance does not affect the level of sales of cars of this brand, since the cars have proven themselves exclusively on the positive side.
After the creation of the first internal combustion engine, questions arose almost immediately about its improvement and increase in power. The first engine was single-cylinder, and the simplest solution immediately suggested itself to increase its power - to increase the number of cylinders. But the next steps in the development of internal combustion engines were not so obvious, since these several cylinders can be arranged in different ways - vertically in a row one after the other, at an angle or horizontally. This last option was called the boxer engine, i.e. engine, the cylinders of which are located horizontally opposite (opposite) each other.
Boxer engine options
However, even such a simple technical solution - to place the engine cylinders horizontally opposite each other, can be implemented in several ways. When such a boxer engine is running, its pistons can move in many different ways.
boxer boxer
During the operation of such a motor, the pistons are always at a distance relative to each other, and each works in its own cylinder - if one is located at the maximum distance from the axis of the engine, then the other, neighboring one, occupies a similar position.
This order of work resembles the movements of a boxer, which is why he received the name "boxer". Very often uses similar Subaru boxer engines. The described engine is shown in the photo below. 
OPOC, the revival of old ideas
Another construction principle implements a boxer engine of the OPOC type. Today they are beginning to develop again thanks to the investments of the notorious Bill Gates. The device of such an engine is shown in the figure below. 
This boxer engine is a two-stroke. The figure clearly shows that there are two pistons in the cylinder, and they are fixed on one crankshaft (in the figure they are indicated as red and blue). Red provides the intake of the mixture, and blue - the release of combustion products. From the design of such a boxer engine, the cylinder head and the valve drive mechanism disappeared. In addition, the advantage of such an opponent is that the pistons work on one crankshaft.
All this significantly reduced the weight of the boxer engine and significantly expanded the scope of its use. Another feature is that it can be either diesel or petrol. It is imperative to clarify that, like any two-stroke engine, it needs to purge the cylinders. For this, an electric motor powered by an external source is used. When the boxer engine enters the mode, the electric motor is turned off and the air supply device turns into a turbocharger.
Considering the design of such a boxer motor, its advantages should be noted: an increase in efficiency provided by the fact that expanding gases press on two pistons, and not on the wall of the combustion chamber, as well as increased force on the shaft. In addition, each piston travels a shorter distance, which reduces friction and, consequently, losses.
Considering other advantages that such a boxer engine promises, it is worth noting that the manufacturer reports that when it is used as a diesel engine, then:
- such an engine is fifty to thirty percent lighter than a conventional turbodiesel;
- such a power unit contains fifty percent fewer parts than a conventional diesel engine;
- takes up fifty to forty-five percent less space under the hood;
- 50-45% more economical.
However, it should be borne in mind that such a boxer power unit is still quite crude, which means that the noted advantages reflect to a greater extent the expectations of its developers.
Boxer tank engine
Yes, there was such an engine, this is the 5TDF, designed for the T-64 tanks, as well as subsequent T-72s and others. Then it provided the necessary power for the given dimensions. A similar boxer engine and its device are shown in the figure below. 
As can be seen from the figure, his pistons are located in one cylinder and move in the opposite direction, but each work on its own crankshaft. With a minimum distance between the pistons, a combustion chamber is formed between them, where the fuel is ignited. There is a boxer engine, both petrol and diesel. By analogy with OPOC, turbocharging is used to supply air to the cylinders, as well as remove exhaust gases.
The used principle of the oncoming movement of the pistons made it possible to simplify the design, ensure the power and compactness of the power plant. So, a similar diesel boxer power unit at two thousand revolutions, a volume of thirteen and six tenths of a liter produced seven hundred horsepower, while taking up a minimum of space.
What is good and bad for an opponent?
It should be noted that in the history of the car, many manufacturers at different times used the boxer engine, trying to realize the advantages provided by it. However, at the moment, more often than others, SUBARU uses such engines in its cars. 
It should be noted right away that it is the device of the boxer power unit that provides its advantages when installed on a machine:
- low center of gravity of the car, which gives it additional stability when driving;
- reduction of both noise and vibration due to the movement of the pistons towards, due to which the boxer engine is considered quieter than similar in-line engines;
- a significant resource, reaching a million kilometers with proper operation.
However, everything is not always good, there are minuses and shortcomings in the opposition. Of these, it is worth noting:
- repair of such a motor is very difficult;
- the engine device is also quite complex, and accordingly, it has a high price;
- maintenance costs are high, and the maintenance itself is extremely costly and inconvenient, requiring highly qualified performers;
- increased oil consumption during operation.
Despite the noted disadvantages and shortcomings, a number of cars (the already mentioned SUBARU and some Porshe models) are equipped with boxer power units. We must think that manufacturers accurately weigh their advantages and disadvantages and consciously go for the use of such a motor.
For internal combustion engines, the horizontal arrangement of cylinders is only one of the possible construction options, but nevertheless, in this case, the resulting boxer engine has great potential and significant prospects for use in a car.
