What is preferable to choose between inline engines and V-engines

What is preferable to choose between inline engines and V-engines

Many motorists are pleasantly pleased with the fact that there is a huge range of vehicles on the market. They differ from each other not only in appearance, brand or body design. A big difference can be observed in the under-hood, where the engine is located.

The question of which engine is better: in-line or V-shaped, becomes relevant only when comparing the ICE with 6 cylinders. Exactly with 6 starts the countdown of the minimum number of cylinders on the so-called V-shaped motors, while in-line engines often have no more than 6 working cylinders, most often having 2-4 units.

Speaking of why a V-shaped power unit is better than a more classic inline engine, it is impossible not to touch upon the opposition engine as well. Some consider it a variation on the V-like unit, while others call it a completely independent and independent type of motor design.

A brief characteristic of engines

The most common and at the same time the most simple layout of the engine is rightly considered an in-line arrangement of cylinders. The bulk of the internal combustion engines with a relatively small volume, made it so. They are compact, have light weight, so without much trouble located in the hood.

But in-line ICEs also have their disadvantages. As the number of cylinders increases, the total length of the motor increases noticeably. The more cylinders in a row, the more vibration occurs during operation. Plus these models require heavier crankshafts. Placing the engine longitudinally increases the risk of severe injuries in accidents and collisions, because this way it is much easier for the engine to dent the engine shield and end up in the cabin.

You should know about V-shaped engines, at least that their minimum number of cylinders is 6. There are three cylinders in each row. Externally it resembles the letter V of the Latin alphabet, hence the corresponding name. With this arrangement, the number of cylinders can be up to 12.

The main advantage is the ability to accommodate a voluminous and powerful power unit in a small underhood space. In terms of safety, they are also superior to their inline competitors. But talking about what the V-shaped car engine is better than the classic inline motor, it is impossible not to mention its disadvantages. Such motors are structurally more complicated, which makes V-engines cost the road. In this format, it’s simply unprofitable for automakers to create engines with small displacement and capacity. Also here the center of gravity is quite high, which creates additional difficulties in the creation of sports cars.

The V-engine is different in that the camber of the block here is 60 or 90 degrees, although there are some exceptions. But if the same camber on the V engine is increased to 180 degrees, then you will see a standard opposition unit or just a boxer. It is marked with the letter B. This name is due to the fact that the cylinders are located opposite each other. In the course of work they make movements, as if waving their hands, like boxers. The effect of the fight between the pistons and led to the appearance of the name Boxer.

If to speak about balance, the six-cylinder opposed engines are not inferior to in-line sixes. The low center of gravity, which none of competitors can boast, speaks in favor of the opposition engine. This is an excellent quality when creating sports car models.

But 6-cylinder opposition engines are quite rare. The main emphasis is made on the 4-cylinder versions. Moreover, even diesel engines have already appeared, which can rightly be called a breakthrough in the automotive industry.

Advantages and disadvantages of inline six-cylinder engines

In the 21st century, the popularity of six-cylinder inline engines began to plummet. They have effectively become extinct as more efficient and productive V-type counterparts have emerged. Hence many people have a legitimate question concerning the difference between these internal combustion engines, and whether the inline motor really has no chance against the V-engine.

Each of you has already realized that the main difference is in the arrangement of the cylinders. In the case of in-line (R) they are arranged in one line (In Line) or row, and in the case of V layout they are opposite each other, externally creating the letter V.

It is not necessary to make hasty conclusions, immediately making V motors the obvious favorites in this confrontation. It is worth looking at the main advantages, as well as listing the disadvantages of each of the engines.

To the strengths of inline ICE, experts include the following points:

• In the case of the inline layout turns out a fairly simple and reliable design. This does not depend on the number of cylinders.
• Block fabrication is simpler, it does not require a second set of cylinder heads and camshafts, which is not the case with V-type competitors.
• Instead of using 4 short camshafts, in-line sixes use 2 long shafts.
• In-line engines are easier to repair and maintain, as access to major components such as spark plugs or high-voltage wires is easy and open.
• Almost all car mechanics like to work with inline motors, because there are no significant difficulties with their repair or routine maintenance.
• One of the key advantages is rightly considered to be the balancing of the internal combustion engine.

Balancing is accomplished through proper duty cycle. In fact, balancing is achieved by reciprocating movements of the pistons. This does not require any complex solutions. In-line ICEs have smooth revs and don’t cause strong vibrations.

But not everything is as perfect as it may seem at first glance after studying the advantages. In fact, the work and design of the inline engine has a number of reasons, due to which the popularity of such an engine declined sharply with the emergence of more modern V6.

• One of the main problems is considered placement. The large number of cylinders does not allow them to be placed in a single row in the underhood of many cars.
• With the transverse placement of the inline engine there is no space for drives and transmission, without which it is impossible to do in cars with front-wheel drive.
• Such engines can’t boast of versatility, which is why car manufacturers refuse to use them. It is much more advantageous to make a V6, which can be placed under the hood of several models.
• The weak side is the stiffness of the long inline engine. The crankshafts and camshafts are long, which can cause them to sag when turning.
• The stiffness of the cylinder block in inline engines is inferior to the V6.
• In-line sixes have a bad effect on the vehicle’s center of gravity because of their higher location.

But it is still impossible to unequivocally state which engine is better in the end, comparing the inline and V-shaped powertrain with each other.

Pros and cons of V-engines

Today’s revving six-cylinder engines are mostly represented by the V pattern. They have a larger diameter, piston stroke and displacement.

The displacement is one of the main design features of an engine. It is expressed in cubic centimeters, or in liters, which is much more familiar to domestic motorists. This volume is determined by the sum of the working volumes of all the cylinders used on the engine. As for the cylinder, its working volume is defined as the product of the cross-sectional area by the length of the piston stroke. Here we are talking about the distance from the lower to the upper dead center.

Each modern engine has its own cylinder displacement. But there is a general classification, according to which all internal combustion engines are divided into micro-liter, small-liter, medium-liter and large-liter.

If we talk about V-shaped power units, then most often it is the medium and large-capacity versions, since it is more advantageous and practical to use an inline configuration in compact cars.

The V-motors’ camber is mainly 60 or 90 degrees. Although there are some exceptions, but they do not affect the overall picture significantly. The main advantages are compactness, minimum space requirement with sufficiently solid power. This same feature allows you to put the same engine in different models, including large cars and compact city cars with a small size of the hood space.

By getting more space under the hood, the automaker has an excellent opportunity to install the same turbochargers or other additional equipment.

In fact, the emergence of the V6 was a great opportunity to offer the same model with a standard 4-cylinder low-power engine, as well as charged and sports versions of the same vehicle, without conducting any serious modifications, changes and upgrades.

But behind such obvious advantages there are obvious disadvantages.

• Balance problems. With the same number of cylinders as an inline motor, V-sixes are inferior in terms of balance.
• In fact, they are two in-line engines with 3 cylinders combined into one design.
• A special balancer shaft is required on all V-twin engines. It serves to balance the engine during operation.
• The absence of balancers leads to strong vibrations occurring during reciprocating movements of the pistons.
• As the engine displacement increases, the balancing becomes worse as the piston stroke and cylinder size increase.
• Counterweights complicate the design of the powertrain.
• The V6 is more difficult to produce, as are all other V-shaped units.

Now that inline sixes are a thing of the past, V6s are firmly in this segment. Whether the situation can change anytime soon is unknown. Although some automakers are already declaring their intentions to bring back inline engines, imposing the fight on the V-twin. Now it will be interesting to see if they succeed or not.

Who to give their preference to

It is only true to compare inline and V-engines with regard to the 6-cylinder engines, since the manufacturers offer the corresponding layouts for both cases.

If among the inline variants, 4-cylinder designs are the norm and are among the most common, then in the case of the V-twin, counting begins only with 6 cylinders, ending with 12 units of working elements of the internal combustion engine.

Which of these to choose, everyone decides for himself. Here, the car buyer should pay attention to what he expects from the motor, and what operating conditions he is counting on.

The V-shaped ICE will be an excellent choice for those who want to take the car with a powerful and tractive engine, maybe even with a turbocharger. In-line engines are considered to be the destiny of small-capacity cars. Four working cylinders, set in a row, do not require a lot of space, easily placed under the hood of many compact cars, give good performance and productivity.

Currently, the most widespread internal combustion engines are in-line 4-cylinder units. But this does not mean that they are the best. In their favor speaks the simplicity of design. Such engines are technically and economically simple. Four cylinders allow arranging them in a row across or along the underhood space, to be completed with different transmissions.

At the same time, in-line four-cylinder engines have one disadvantage associated with the limited working volume. Such engines are available with a capacity of 1 to 2.5 liters. For production cars this is often enough. But if it is necessary to raise the power and increase productivity, it is necessary to add the number of cylinders. This is where the V-shaped power unit comes to the fore.

Types of engines: V-shaped, opposed, in-line: differences and subtleties

Growth of power, rpm and a fierce fight for cost reduction have settled everything in its place. The simplest single-cylinder engine is a thing of the past for automobile manufacturers. The average cylinder engine capacity of an ordinary car now – from 300 to 600 cubic centimeters (plus or minus a hundred “cubic meters” in exceptional cases, such as a three-cylinder sidecar Smart or in-line 4.5-liter “six” off-road Nissan Patrol). The liter output ranges from 35 hp/L for the naturally aspirated diesel to 100 hp/L for the boosted gasoline engine. For serial engines this is an optimum, to go beyond which it is simply unprofitable. Today the 100 hp engine will have four cylinders, the 200 hp engine will have four, five or six cylinders, the 300 hp engine will have eight… But how to arrange these cylinders? In other words, what is the layout of a multi-cylinder engine?

Simplicity is worse than compactness What is the designer’s headache? First, about how to simplify the engine design, so that it would be cheaper to produce and easier to maintain. The simplest engine – in-line (we will call such engines with the indices R2, R3, R4, etc.). If you arrange in a row the required number of cylinders, you get the required displacement. Two- and three-cylinder engines are not met in automobiles very often, including in-line engines. But the inline four is in the most mass range of passenger car displacement – from 1.0 to 2.3 liters.

In-line three-cylinder horizontal motor in Subaru E-series vans (displacement – 1.0 or 1.2 liters) is equipped with a balancer shaft

Five-cylinder in-line engines appeared on production cars recently, in the mid-1970s. The first has been Mercedes-Benz with its diesel five – they appeared in 1974 (on the model 300D with body W123). Two years later saw Audi’s five-cylinder two-liter gasoline engine. And in the late ’80s such engines were made by Volvo and FIAT. In-line sixes, so popular in Europe until recently, became extinct in a moment. And nothing to speak about in-line “eight” – it became extinct already in 30th. Why? The answer is simple. With the increasing number of cylinders the engine becomes longer, and it creates a lot of inconveniences. For example, to squeeze in through the engine bay of the front-wheel drive car in-line six managed in a few cases – you can recall only British Austin Maxi 2200 of the mid-60s (then the designers had to hide the gearbox under the engine) and the newest Volvo S80 with a super-compact gearbox. How to shorten an inline motor? It can be “sawed” in half, put the two halves next to each other and make it run on one crankshaft. Such engines, which cylinders are located in the form of the Latin letter V, are half as short as in-line ones – the most widespread are engines with the block angle of 60o and 90o. A V-shaped motor with the block angle of 180 o, where the cylinders are located against each other, is called an oppositional (or “boxer” – designations B2, B4, B6, etc. derive precisely from the word boxer).

These engines are more complicated than in-line engines – for example, they have two cylinder heads (each with its own gasket and manifolds), more camshafts, more complex scheme of their drive. Opposite engines also take up a lot of space in width. Therefore, for layout reasons, they are used quite rarely – the manufacturers of “boxers” can be counted on the fingers. And how to make a V-engine even more compact? One of the simple, at first glance, solutions is to make the block angle less than 60 o. Indeed, such engines were, but rarely – you can remember, for example, the cars Lancia Fulvia of the 70-ies with engines V4, which had the angle of camber of 23 °. Why this was not used by all? The fact is that the engine designer is always faced with another problem – vibration.

About forces and moments In general, an internal combustion piston engine cannot work without vibrations – that’s how it is designed. But it is necessary to struggle against them, and not only to increase passengers’ comfort. Strong unbalanced vibrations can cause destructions of engine parts – with all consequences flying out and falling out… What causes vibrations? Firstly, in some engine schemes, cylinder bursts occur unevenly. Designers avoid such schemes if possible, or try to make the flywheel more massive – this helps smooth out torque pulsations. Secondly, as the pistons move up and down, they either accelerate or decelerate, which creates forces of inertia – they are akin to those forces that make the car’s passengers bow during braking or push them into the backs of seats during acceleration. Thirdly, the connecting rod in the engine does not move up and down at all, but performs a complex motion. And the reciprocating movement of the piston from the top dead center to the bottom also cannot be described by a simple sine wave. Therefore, among the forces of inertia, there appear components with doubled, tripled, quadrupled crankshaft rotation frequency… These so-called forces of inertia of higher orders are usually neglected – they are very small compared to the main force of inertia (which was assigned the first order). The exception is the forces of inertia of the second order, which have to be reckoned with. Plus, pairs of forces applied at a certain distance form moments – this is what happens when the forces of inertia in neighboring cylinders point in different directions. What can be done to balance the forces and moments? First, you can choose an engine diagram in which the cylinders and crankshaft crankshaft crankshaft are arranged in such a way that the forces and moments will mutually balance each other – they will always be equal and directed in opposite directions. And if none of the balanced schemes is suitable – for example, for layout reasons? Then you can try to position the crankshaft journals differently and use all sorts of counterweights that create forces and moments equal in magnitude but opposite in direction to the main balancing forces. Sometimes this can be done by placing counterweights on the crankshaft of the motor. Or sometimes on additional shafts called counter-rotating balancer shafts. They are so called because they rotate in a different direction than the crankshaft. But this makes the engine more complicated and expensive. To make it easier to describe the degree of equilibrium of different engines, we have prepared a summary table. The self-balanced forces and moments are highlighted in green, and the free ones (those that are not balanced and break free – through the power unit supports go to the car body) are highlighted in red. What do we get? Only two from widespread types of engines are absolutely balanced – these are in-line and opposed “sixes”. Now do you understand, why BMW and Porsche so firmly hold on such engines? Well, we have already mentioned the reasons why others refuse them. Now let’s consider other schemes in detail.

An example of in-line four with balancer shafts is Saab’s 2.3-liter engine. Shafts are on either side of the crankshaft and revolve at double speed in opposite directions

The Fiat TD 125 five-cylinder turbodiesel with 2,387 cc is formed by adding one cylinder to the 1.9-liter

Of two-cylinder engines, only one is currently used on cars – a two-cylinder in-line motor with a crankshaft with cranks pointing in one direction (for example, such an engine is on the domestic Oka). As you can see, this engine is similar to a single-cylinder engine in terms of balance, since both pistons move up and down simultaneously, in phase. In order to balance the free forces of inertia of the first order, there are two shafts with counterweights on the left and right of the crankshaft in the Oka engine. But what about the forces of the second order? In order to cope with them, it would be necessary to add two more balancer shafts, which on a two-cylinder motor, originally designed for small and cheap cars, would be quite inappropriate. However, this is nothing – many two-cylinder engines were produced without balancer shafts. So it was, for example, on little Fiat 500 of 1957. Yes, there were vibrations and they tried to dampen them with a power unit suspension… But the engine was simple and cheap! Two-cylinder engine, with cranks directed in different directions (180 o), could be found only on motorcycles. Since the pistons in it always move in antiphase, it is better balanced. However, even alternation of flashes in the cylinders can only be achieved on two-stroke engines – such engines could be found on pre-war DKWs and their direct successors, the plastic Gaedar Trabantes. Because of simplicity and cheapness, there were no balancer shafts, and the vibrations were tolerated. Only one car with a twin-cylinder V-engine comes to mind – the domestic NAMI-1.

And till our days, this type of engine has survived only on motorcycles – just remember the American Harley Davidson and its Japanese followers with their V-shaped twins in all their chrome glory. Such an engine can be balanced almost completely with the help of counterweights on the crankshaft, but it is impossible to achieve a uniform alternation of flashes. It’s good that bikers don’t pay much attention to vibrations… The cars with an opposition engine, the most balanced of all two-cylinder engines, were few – for economic and layout reasons. One can mention, for example, French Citroen 2CV.

The three-cylinder engine is less balanced than the inline four, and that’s why manufacturers of three-cylinder engines – such as Subaru and Daihatsu – try to equip them with balancer shafts. However, Opel engine builders, who recently equipped the Opel Corsa with a new three-cylinder motor Ecotec family, and the designers of the engine “city coupe” Smart for cheapening and reducing mechanical losses refused from the balancer shaft. True, the three-cylinder Corsa has already been criticized by German car journalists: “It’s absolutely impossible to drive around town in alternating modes.” In the most popular among the motorists inline four there is still the free force of inertia of the second order. It can be balanced only by balancer shaft, rotating with double speed (haven’t you forgotten – the force of inertia of the second order acts with double frequency?). And to compensate for the torque from the balancer shaft, you would have to put another one rotating in the opposite direction. Expensive? Undoubtedly. However, you can find engines with balancer shafts on Mitsubishi, Saab, Ford, Fiat, VW. The most recent example is the 2.2-liter four from the Opel Ecotec family.

By the way, the opposition “four” is balanced better than in-line – here there is only a moment from forces of inertia of the second order, which tends to turn the engine around the vertical axis. However, both the air-cooled “opposition” of the legendary Beetle and the famous “boxers” of Subaru did and do without balancer shafts.

As for inline 5’s, things are not so good with equilibrium. The forces of inertia are compensated, but the moments from these forces… When the engine works, the bending moment wave constantly “runs” along the block, therefore the block must be rather rigid. However, Mercedes-Benz, Audi and Volvo also struggle with vibrations by refining the power unit suspension. Only the Fiat motorists use a balancer shaft, which completely balances all the moments. By the way, practically all A’s are formed by adding one more cylinder to the four-cylinder engine – like cubes in a construction set. They do it in order to get more powerful engines with minimum production and design costs. Thus all the stuffing, including pistons, rods, valves, etc., can be taken from the “four”. It will need other cylinder block and head, and of course the crankshaft, which crankshafts should be located at an angle of 72 °. We’ve already mentioned the six-cylinder engines – a dream in terms of equilibrium. But in V6 engines, which are replacing in-line ones, the situation with balance is the same as in “three-cylinder”, that is not good. Therefore, the balancer shafts can be seen on the Citroen/Peugeot three-liter V6 engine or on the new 3.2-liter Mercedes-Benz M112 engine. On other engines, they try not to complicate the design and try to reduce the vibration level to a minimum due to improved suspension of the power unit and cleverly shifted crankshaft crank journals (as, for example, on Audi V6). Let’s add one more note here – V6 engines with a 90-o camber do not ensure uniform alternation of flashes in the cylinders. The resulting unevenness can be compensated by a weighted flywheel, but only partially. Here is another source of vibrations… V-eights with the angle of cylinder camber in 90o and the crankshaft, which cranks are located in two mutually perpendicular planes, are quite well balanced. In such a motor, it is possible to ensure uniform alternation of flashes, which also works for smooth running. Two moments remain unbalanced, which can be completely pacified with two counterweights on the crankshaft – on the cheeks of the outermost cylinders. Do you understand why Americans felt the charm of V-engines earlier than others? They don’t like vibration and jolting in their cars… Finally, we can talk about unusual schemes. First, you can think of V4 engines. There were few of them – the European Ford of the 60’s (which was in the Ford Taunus, Capri and Saab 96) and a miracle engine of domestic Zaporozhets. Here the balancing shaft for the momentum from the forces of inertia of the first order couldn’t be avoided. However, the designers of the above mentioned cars chose this scheme for compactness and partly for economy, but not for a good equilibrium. And what about the V-shaped “tens”? As you can see, the degree of equilibrium of such motors is exactly the same as of the R5 motors. However, the designers of some motors of Formula 1 or monsters Chrysler Viper and Dodge RAM, where there are V10 engines, do not think about vibrations in the first place.

Well, other schemes can be easily reduced to the previous ones. For example, an opposition “eight” (example of application – the Porsche 917 race cars) is two “fours”, working for one crankshaft. And the V-shaped and opposed twelve-cylinder engines can be reduced to two inline sixes.

VR6, VR5, W12… Remember, we mentioned V-shaped engines with small block angle, like on the Lancia? Earlier, these schemes were avoided – it is more difficult to balance them than engines with a 60 o or 90 o camber, and the benefit in compactness was not so appreciated then… But now the situation has changed. Firstly, hydraulic supports for the power unit have been created and are used, which can significantly attenuate vibrations. Secondly, nowadays the space under the hood is by weight of gold. In fact, who could imagine a modest hatchback with a 2,8-liter engine before? And now – here you are: VW Golf VR6 of the previous third generation! This famous Volkswagen VR6 engine, the “V-row” motor (the designation VR stands for it) was a further development of the V-engines with a low camber. The cylinders of this engine are bifurcated to an even smaller angle than on the Lancia – only 15 points. An ingenious solution – the 2.8-liter “six” is more compact than a conventional V6 engine, and even has one cylinder head! And last year the Volkswagen Golf IV was equipped with the VR5 engine, which is a VR6 engine from which one cylinder was “cut off”. After that, the motorists from VW concern got off the chain.

They came up with an extremely compact W-engine. The W12, which is equipped with concept car W12 Roadster, is two VR6 engines mounted at an angle of 72 o on one crankshaft. The W8 engine that will power the VW Passat Plus is two VR6 engines that have been “cut off” two cylinders each, and they are also combined into one block on the same crankshaft. And also in Wolfsburg, they’re thinking about an eighteen-cylinder engine – it’s scary to think what letter it will look like… Why haven’t there been such engines before? We have already mentioned the new hydraulic supports. There are reasons of purely technological nature. Look, for example, at the crankshaft of the W12 engine – the technologist wouldn’t dream of such a thing! And also the creators of new schemes are helped by… the computer. To calculate all variants of the angle of camber, location of crank journals, the order of flashes in the cylinders and to choose the most balanced one, it is very difficult to do without the computer.

Theory and practice As you can see, when selecting the scheme of the power unit, the designers do not put the degree of equilibrium at the forefront. The main thing is to successfully fit such an engine into the engine compartment, which will have the best ratio of weight, size and power. Then, engines nowadays are increasingly built according to the modular principle, and this has culminated in Volkswagen’s extravagances. Speaking simplistically, any engine can be built on one piston group – both three-cylinder and W12. And vibrations… Firstly, it is necessary to distinguish theoretical and real equilibrium of the engine. If the crankshaft assembly with flywheel is out of balance, and pistons and rods differ appreciably in mass, even the straight-six will shake. And then, the actual balance is always much worse than the theoretical one – for reasons of deviation of parts from nominal dimensions and because of deformation of parts under load. So vibrations “break through” from the engine to the outside in any scheme. That’s why automotive engineers pay so much attention to the powertrain suspension. In fact, the design and positioning of the engine supports is no less important than the degree of equilibrium of the motor itself…

The W-shaped super-engine, which so far stands on the VW W12 concept roadster and coupe, is two VR6 cylinder blocks (the photo clearly shows the staggered arrangement of the cylinders) united in one casting at an angle of 72 o. The 5.6-liter 420-horsepower engine is only 51 cm long and 70 cm wide.