Flat engine

A flat engine is an internal combustion engine with horizontally-opposed cylinders. Typically, the layout has cylinders arranged in two banks on either side of a single crankshaft and is otherwise known as the boxer, or horizontally-opposed engine. The concept was patented in 1896 by engineer Karl Benz, who called it the "contra engine."[1][2]

A boxer engine should not be confused with the opposed-piston engine, in which each cylinder has two pistons but no cylinder head. Also, if a straight engine is canted 90 degrees into the horizontal plane, it may be thought of as a "flat engine". Horizontal inline engines are quite common in industrial applications such as underfloor mounting for buses.

True boxers have each crankpin controlling only one piston/cylinder while the 180° engines, which superficially appear very similar, share crankpins. The 180° engine, which may be thought of as a type of V engine, is quite uncommon as it has all of the disadvantages of a flat engine, and few of the advantages.

The boxer engine was first patented by German engineer Karl Benz in 1896.
Moteurs à Plat - V à 180° vs. Boxer
Difference between two flat 6 cylinder engines: 180° V on the left, boxer on the right

Boxer engine

1954 BMW R68 engine. The two cylinders are offset.

In 1896, Karl Benz invented the first internal combustion engine with horizontally opposed pistons.[1] He called it the kontra engine, as the action of each side opposed the action of the other. This design has since been called the "boxer" engine because each pair of pistons moves in and out together, rather like the gloves of a boxer.[3] The boxer engine has pairs of pistons reaching TDC simultaneously.[3]

The boxer configuration is the only configuration in common use that does not have unbalanced forces with a four-stroke cycle regardless of the number of cylinders, as long as both banks have the same number of cylinders. These engines do not require a balance shaft[4] or counterweights on the crankshaft to balance the weight of the reciprocating parts, which are required in most other engine configurations. However, in the case of boxer engines with fewer than six cylinders, unbalanced moments (a reciprocating torque also known as a "rocking couple") are unavoidable due to the "opposite" cylinders being slightly out of line with each other.[3] Other engine configurations with natural dynamic balance include the straight-six, the straight-eight, the V12, and the V16.

Boxer engines (and flat engines in general) tend to be noisier than other common engines for both intrinsic and other reasons.[5] In cars, valve clatter from the engine compartment is not damped by air filters or other components.[6]

Aviation use

ULPower UL260i
UL260i flat-4 aircraft engine

In 1909 Santos Dumont used Dutheil-Chalmers and Darracq boxer engines in his Demoiselle airplane, the first airplane with significant production (over 40).

Multi-cylinder boxer layouts have proved to be well suited as light aircraft engines, as exemplified by Continental, Lycoming, Rotax, Jabiru and Verner.[7] An important factor in aircraft use is the flat engine's absence of vibration, which allows a lighter engine mount.

General aviation aircraft often use air-cooled flat-four and flat-six engines made by companies such as Lycoming and Continental. Ultralight and microlight aircraft often use engines such as the Rotax 912 and Jabiru 2200.

Riedel starter for German WWII jet engines, with pull-start handle and cable

During the Second World War, Boxer engines were used as a starter motor for the first German jet engines to power up the engine at cranking speed. The two-cylinder two-stroke flat engine was developed by Norbert Riedel ("Riedel starter"), had a cylinder capacity of 270 cc and a power of 8 kW (10.5 hp) at 7150 rpm and essentially functioned as a pioneering example of an APU for starting a jet engine. It was an extreme short stroke (bore / stroke: 70 mm / 35 mm = 2:1) design so it could fit in the hub of the turbine compressor and started electrically or with a pull starter. The engine was produced by the Victoria works in Nuremberg and served as a starter for the jet engines Junkers Jumo 004 and BMW 003.

Motorcycle use

Flat engines offer several advantages for motorcycles, namely: a low centre of gravity, smoothness, suitability for shaft drive, and (if air-cooled) excellent cooling of the cylinders.[1][8]

The first motorcycle with a boxer engine was the 1905 Fée flat-twin, which was developed into the 1907 Douglas. Douglas would continue making flat-twin motorcycles until 1957, ending with the Dragonfly. BMW have made motorcycles with flat-twin engines since the BMW R32 of 1923. Unlike contemporary Douglas motorcycles, which had their engines mounted with the cylinders in line with the frame, the R32 had its cylinders mounted across the frame and used a shaft to drive the rear wheel. The drivetrain layout of the R32 has been used, with improvements, in all subsequent BMW flat-twin motorcycles. The Russian Ural and Ukrainian Dnepr flat twins were copies of the pre-WWII military plunger-suspension BMW R71.

In 1923, Max Friz designed the first BMW motorcycles, choosing a 500 cc boxer engine and unit transmission with shaft drive. This engine type is still in production today.[1] The BMW 247 engine, known as an airhead due to its air cooling, was produced until 1995. BMW replaced it with the oilhead engine with partial oil cooling and four valves per cylinder, but still retained the same flat-twin configuration. In 2013, BMW introduced partial ("precision") water-cooled version, first on their BMW GS and planned to replace all oilheads.[9]

Flat-four engines have been used in the 1938–1939 Zündapp K800, the French BFG motorcycle with the Citroën GS engine, and the Honda Gold Wing from 1975 to 1986. Gold Wings since 1987 have used flat-six engines, as have Honda Valkyries.

Automotive use

Diesel Engine Type DS140 2C Hino
1969 Hino Motors DS140 12-cylinder boxer diesel engine

The low centre of gravity allowed by a flat engine can reduce body roll in automobiles and enhance handling precision.[4] Historically they could be found in cars manufactured by companies such as Porsche, Lancia, Benz, Ford, Tatra, Citroen, Alfa Romeo, Jowett, Rover, Volkswagen, Chevrolet, and Ferrari. The most prominent manufacturers currently using a boxer engine as their primary engine configuration are Porsche and Subaru.

Automobile layouts used with flat engines

Blackjack Avion-engine
Citroën 2CV drivetrain, including overhanging front-mounted flat-twin engine and shafts to front wheels, in a Blackjack Avion three-wheeler

When mounted longitudinally in a vehicle, flat engines with up to six cylinders are short, low, and wide. As a result, they have often been used in compact drivetrains where the engine is mounted outside the wheelbase and drives the nearer pair of wheels through the transmission without a drive shaft.[10] The short length of a longitudinally mounted flat engine with six cylinders or fewer makes it ideally suitable for air cooling.[11]

Examples with rear-engine, rear-wheel-drive layouts include the two-cylinder BMW 600 and 700, four-cylinder Tatra 97, Volkswagen Beetle and Porsche 356, and the six-cylinder Chevrolet Corvair, Porsche 911, and Tucker 48. All of these examples except the Tucker and later versions of the Porsche 911 are air-cooled.

Examples with front-engine, front-wheel-drive layouts / four-wheel drive layouts include two-cylinder Citroëns and Panhards and the four-cylinder Citroën GS, Lancias from the Flavia to the Gamma, Alfa Romeo Alfasud and Subarus DL and GL. The Citroëns and Panhards are air cooled while the Lancias, Alfa Romeos and Subarus are water cooled.

Tatra 11 backbone chassis with front-mounted flat-twin engine and rear final drive

Flat engines have also been used in cars with front-engine, rear-wheel-drive layouts, including Bradford trucks and vans, the Glas Isar, Jowett cars and trucks, early Tatras, the Scion FR-S and the Subaru BRZ.

Flat engines, including non-boxer flat-12s, have been mid-mounted in Porsche and Ferrari racing cars. Porsche has made the 914 for road use with four or six cylinder air cooled boxer engines, while Ferrari road cars with mid-mounted water cooled non-boxer flat-12s include the 365 GT4 BB, BB 512, BB 512i, Testarossa, 512 TR, and F512 M.

Subaru use a four-cylinder flat engine at the front of the car that drives all four wheels. The front half-shafts come out of a front differential that is part of the gearbox. A rear driveshaft connects the gearbox to the rear half-shafts.


In 1901, the Wilson-Pilcher car was launched with the choice of a flat-four or flat-six engine mounted at the front of the car with the crankshaft in-line. The water-cooled engines had 95 mm bore and stroke, and the crankshaft was supported with intermediate bearings between each pair of cylinders.[12] The cars were made in London until 1904 when Armstrong Whitworth took over the manufacture, which continued until c. 1907. These cars "created quite a sensation in automobile circles at the time on account of its remarkably silent and smooth running, and of the almost total absence of vibration."[12]

In 1902 the Buffum automobile was equipped with opposed four cylinder engines that were rated at 16 horsepower. Herbert H. Buffum produced an American Automobile called the Buffum in Abington, Massachusetts from 1903 to 1907.[13]

Early Fords, including the original Model A, the Model C, and the Model F were powered by flat-twin engines.

In the 1920s and 1930s Tatra made a series of automobiles with front-mounted air-cooled flat engines, including the flat-twin 11 and 12 and the flat-four 30, 54 and 75. In the late 1930s Tatra built the rear-engined 97 with a rear-engined flat-four.

Ferdinand Porsche developed the KdF-Wagen partly based on the Tatra 97. Like the 97, the KdF-Wagen had an air-cooled flat-four engine The KdF-Wagen was renamed the Volkswagen and a limited number were made before World War II. The factory was reopened after the war, and the Volkswagen became a commercial success in its own right, and also became the base for other designs, including the Type 2 (bus) transporters, the Karmann Ghia, Volkswagen Type 3 cars and the SP2 sports car. The last versions of the Volkswagen boxer were watercooled and thus dubbed the Wasserboxer (waterboxer) by enthusiasts. This engine included many developments of the earlier engines. It was offered in capacities of 1.9 and 2.1 litres to power Type 2 (T3) buses and transporters.

In 1948 Preston Tucker modified a helicopter flat-six to be rear-mounted in his Tucker 48.[1]

The Citroën 2CV, development of which began before the Second World War, was introduced in 1948 and ended production in 1990. Later developments of the 2CV, which also used derivatives of its air-cooled flat-twin engine, included small commercial vehicles, the Ami, and the Dyane. The Visa and Axel, which replaced the Ami and the Dyane, also offered derivatives of the 2CV's flat-twin as their base engines. The Citroën GS, introduced in 1970, had a flat-four engine, which was also used in the Ami Super and in Romania's Oltcit Club.[14] A flat-six was proposed for the Citroën DS but rejected.[15]

Panhard began making front-drive cars with air-cooled flat-twin engines in 1948 with the Dyna X. They continued with this formula through the Dyna X, the PL 17, and the 24. Panhard, which had been absorbed into Citroën by 1965, stopped making passenger cars in 1967 and made only military vehicles thereafter. During the 1950s, one of Panhard's military vehicles, the EBR, used a flat-12 engine.

In 1959, for the 1960 model year, Chevrolet introduced the Corvair, a compact car with a rear-mounted air-cooled flat-six. The car's overhead valve Chevrolet Turbo-Air 6 engine displaced 2.3 litres at introduction and was increased to 2.7 litres in 1964. A turbocharged version raised output to up to 134 kilowatts (180 hp). The Corvair flat six used from one (turbocharged) to four carburetors in the 104 kilowatts (140 hp) version.

In 1961, Lancia introduced its flat-four water-cooled engine in the front-wheel drive Flavia. The Flavia engine started at 1500 cc and 90 PS (66 kW) but was eventually enlarged to 2000 cc with 142 bhp (106 kW) in 1970, the year in which it was given the first Bosch electronic injection in a flat four engine. Lancia built a 2484 cc flat-four engine in 1976 for the larger Gamma model. Production of the Gamma, along with Lancia's last flat-four engine, ended in 1984.

The Toyota U engine was a flat-twin introduced in the Toyota Publica in 1961. The 697 cc Publica had what was then the conventional layout of front engine and rear drive. The engine size was increased to 790 cc for the 2U and 2U-B engines used in Publicas and MiniAces from 1955 to 1976. The 790 cc 2U-C engine was used in the Sports 800, Toyota's first production sports car, from 1965 to 1969. Production of U-series flat-twin engine ended in 1976.

Front-mounted air-cooled flat-twin engines were used in DAF 600, 750, Daffodil, 33 and the 44/46.

The flat-four engines in Alfa Romeo's Alfasud, Sprint, 33 and early versions of the 145/146. The last of the line was a 1,712 cc flat-four, 16-valves, producing up to 137 PS (101 kW).

Ferrari made use of a flat-twelve design in several models, including the Berlinetta Boxer, the Testarossa and their derivatives, although this engine design is technically a V12 that has been flattened down to a 180° configuration, and therefore cannot be regarded as a true boxer engine.[16]

Current users


All early Porsches up to the 914 used air-cooled boxer engines. The 356 and its derivatives had flat-four engines, as did the 912 and the mid-engined 914. The original 911 had an air-cooled flat-six, as did a six-cylinder version of the 914; the later 964 and 993 versions of the 911 used air/oil cooled flat-six engines.

Some Porsche sports racing models, including the 908, used flat-eight engines. The flat-twelve in the 917 model is a 180° V 12 engine; Ferrari's Berlinetta Boxer (BB 512) later used a 180-degree flat 12 for Le Mans to compete with Porsche, but Ferrari also used the BB 512 on road-going cars, unlike Porsche.

Porsche began to use water-cooled flat-six engines in the Boxster in 1996. This type is also used in the Cayman and in 911 models starting with the 996. The 718 Boxster and Cayman have moved from naturally aspirated flat sixes, to turbocharged flat fours, while the 911 uses a smaller turbocharged flat six.


Subaru Boxer Diesel engine for 2008 Legacy in Eco-Products 2008
Subaru boxer turbodiesel engine cutaway display

Since the Subaru 1000 of 1966[17] the water-cooled front-mounted flat-four and flat-six engines have been used by Subaru in all of its mid-sized cars, including the Impreza, Legacy, Outback, and SVX. The Forester and Tribeca SUVs, BRAT and Baja pickup trucks, and BRZ sports car also use boxer engines. Subaru refers to these as boxer engines in publicity commentary, and include a variety of naturally aspirated and turbo driven engines from 1966, when the Subaru 1000 was introduced to current; both closed and semi-closed short blocks have been used. A print ad for the 1973 Subaru GL coupe referred to the engine as "quadrozontal"[18] The EJ series of four-cylinder engines released first in 1990 has been the focus for the development of the boxer engine in the late 20th century. Ranging from 1.5 to 2.5 litres, this engine in its 2-litre turbo arrangement has been the power behind World Rally Championship winning cars. Subaru also offers a common rail boxer turbodiesel,[19][20][21] called the Subaru EE series, the world's first to be fitted into a passenger car.[4]


In a joint venture between Subaru and Toyota, a 1,998 cc flat-four engine with 200 PS (147 kW) having GDI was developed as the Subaru FA20 and Toyota 4U-GSE. This was used in the two-door coupe Toyota 86 and Subaru BRZ.[3]

W Motors

The Lykan HyperSport, the third most expensive car in the world as of 2015, uses a Porsche-derived flat-six engine.

Flat engine designs

See also


  1. ^ a b c d e English, Bob (2010-04-29). "The engine that Benz built still survives". The Globe and Mail. Canada. Retrieved 2013-12-19.
  2. ^ Hodzic, Muamer (2008-03-27). "Mercedes Heritage: Four-cylinder engines from Mercedes-Benz". Blog. BenzInsider. Retrieved 2013-12-20.
  3. ^ a b c d Bonk, Aaron (2013-02-07). "How Boxer Engines Work". Super Street Magazine. Source Interlink Media. Retrieved 2013-12-21.
  4. ^ a b c Hanlon, Mike (2001-02-07). "The world's first horizontally-opposed turbo diesel engine". Gizmag. Retrieved 2013-12-20.
  5. ^ Brown, Stuart F. (2009-07-02). "Handlebars - BMW's Boxer - A Classic Design Is Updated and Refined". New York Times. Retrieved 2013-12-20.
  6. ^ Brown, Warren (2013-12-13). "Subaru Impreza is fun, reliable but has darned noisy engine". The Record. Retrieved 2013-12-20.
  7. ^ "Range of our Engines ‹ Low cost, High value". Verner Motor. 2014. Archived from the original on 2014-10-06. Retrieved 2015-12-28.
  8. ^ Szymezak, Pascal. "Début de la légende". La saga GoldWing (in French). Fédération des GoldWing Club de France. Archived from the original on 2013-12-19. Retrieved 2013-12-20.
  9. ^ Cameron, Kevin (2012-12-21). "BMW's All-New Water-Cooled Boxer – Tech Preview". Cycle World. Bonnier Corp. Retrieved 2013-12-20.
  10. ^ Nunney, M. J. (1988). Light and Heavy Vehicle Technology. Oxford, UK: Heinemann Professional Publishing. p. 12. ISBN 0 434 91473 8. Retrieved 2015-05-08.
  11. ^ Nunney 1988, pp. 12–13.
  12. ^ a b "The Wilson-Pilcher Petrol Cars". The Automotor Journal. 1904-04-16.
  13. ^ "The Buffum Automobile". Farber and Associates.
  14. ^ "Citroën GS + GSA boxer engine". Citroënët. Retrieved 2013-12-20.
  15. ^ "Citroën DS the birth of the goddess". Citroënët. Retrieved 2013-12-20.
  16. ^ "Flat-12 engine". Ferrari.com. Ferrari S.p.A. Archived from the original on 2013-12-25. Retrieved 2013-12-21.
  17. ^ "Distinct Engineering Mounted into the Subaru 1000". SUBARU Philosophy. Fuji Heavy Industries Ltd. 2012-08-10. Retrieved 2013-12-20. Source: 'Subaru' magazine – Subaru 1000 extra edition (issued 1966-05-20)
  18. ^ "» Vintage Subaru Ad (1973 The Subaru GL Coupe)". Scoobyblog.com. Retrieved 2010-09-18.
  19. ^ "Greencarcongress". Legacy Diesel Announcement. Retrieved 2008-01-23.
  20. ^ Harwood, Allyson (January 2008). "2008 Subaru Turbodiesel Boxer - First Drive". MotorTrend Magazine. Source Interlink Media. Retrieved 2013-12-20.
  21. ^ "A True Engineering Revolution". SUBARU BOXER DIESEL. Fuji Heavy Industries Ltd. Retrieved 2013-12-20.

The BMW M2B15 was BMW's first flat-twin engine. Manufactured from 1920 to 1923, the M2B15 was intended to be a portable industrial engine, but it was used by several German motorcycle manufacturers to power their motorcycles.In 1920, BMW engineer Max Friz reverse-engineered the engine of foreman Martin Stolle's 1914 Douglas motorcycle and developed a similar 500 cc side-valve flat engine from it. This was referred to internally as the Type M2B15 and offered for sale officially as the "Bayern Motor". The engine was tried out by various motorcycle manufacturers. Starting in 1920, Victoria of Nuremberg used the engine in their KR 1 motorcycle, and other manufacturers such as SMW and Bison also fitted it.Bayerische Flugzeugwerke used the M2B15 engine in their Helios motorcycle. BMW inherited the Helios when it was merged with BFW in 1922.

Controlled combustion engine

Controlled combustion engine (CCE) is a term used by TechViki, an engine design company, to identify a type of experimental internal combustion engine (ICE) designed by Brad Howell-Smith. It uses two counter-rotating cams instead of a crankshaft. Pairs of cylinders oppose each other in a boxer flat engine or X engine arrangement.

Engine configuration

Engine configuration is an engineering term for the layout of the major components of a reciprocating piston internal combustion engine. These components are the cylinders and crankshafts in particular but also, sometimes, the camshaft(s).

Many apparently 'standard' names for configurations are historic, arbitrary, or overlapping. For example, the 180° V engine is so named because the crankshaft is related to a V engine more closely than it is related to other opposed-piston engines such as the boxer. Others would consider it a flat engine because of its shape.

The names W engine and rotary engine have each been used for several unconnected designs. The H-4 and H-6 engines produced by Subaru are not H engines at all, but boxer engines. The Subaru H-4 and H-6 designs are so named because they are horizontally opposed pistons.

Flat-four engine

A flat-four or horizontally opposed-four is a flat engine with four cylinders arranged in two horizontal banks of two, each bank lying opposite the other, a crankcase between them.

Flat-six engine

A flat-six or horizontally opposed-six is a flat engine with six cylinders arranged horizontally in two banks of three cylinders on each side of a central crankcase. This should not be confused with the Opposed-piston engine. The pistons are mounted to the crankshaft such that opposing pistons move back and forth in opposite directions at the same time, somewhat like a boxing competitor punching their gloves together before a fight, which has led to it being referred to as a boxer engine.

The configuration results in inherently good balance of the reciprocating parts, a low center of gravity, and a very short engine length. The layout also lends itself to effective air cooling. The shape of the engine suits it better for rear engine and mid-engine designs, where the low center of gravity is an advantage; in front engine designs the width interferes with the ability of the front wheels to steer. However, it is an intrinsically expensive design to manufacture, and somewhat too wide for compact automobile engine compartments, which makes it more suitable for luxury sports cars, cruising motorcycles, and aircraft.Only a few auto makers, including Porsche and Subaru, currently use horizontally opposed engines. Porsche continues to be the most prominent manufacturer of flat-6 engine luxury sports cars, while Subaru uses it in its all-wheel drive cars, where the difficulties of fitting the engine between the front wheels are offset by the efficiency of adding four-wheel drive to the layout. In the past a number of other manufacturers have used them, notably Preston Tucker in the 1948 Tucker Sedan and Chevrolet in the 1960s Corvair with the flat-6 air-cooled Chevrolet Turbo-Air 6 engine. The Citroën DS was originally intended to be fitted with an air-cooled flat-6, but this never materialised.

Flat twin engine

A flat-twin is a two-cylinder internal combustion engine with the cylinders on opposite sides of the crankshaft. It is a flat engine with two cylinders. Used in motorcycles for more than a century, flat-twins have also been used in automobiles, light aircraft, stationary powerplants, and household appliances.

Early flat-twin motorcycles' engines were mounted with the cylinders in line with the frame. This caused uneven cooling of the cylinders and required the motorcycle to have a long wheelbase. Later flat-twin motorcycles' engines were mounted with their cylinders across the frame for better air cooling and a shorter wheelbase. Disadvantages of this layout include torque reaction in the motorcycle in turns and the potential to damage cylinder heads.


Haacke is a surname. Notable people with the surname include:

Hans Haacke (born 1936), German artist

Julia Haacke (born 1971), German actress

Julian von Haacke (born 1994), German footballer

Wilhelm Haacke (1855–1912), German zoologistSee also

Haacke HFM-2, was a German two cylinder flat engine built in the early 1920s

Haacke's rock gecko, or Haacke's flat gecko (Afroedura haackei), is a species of African gecko found in South Africa


Haacke HFM-2

The Haacke HFM-2 was a German two cylinder flat engine built in the early 1920s.

Lycoming O-1230

The Lycoming O-1230 was a flat-twelve engine for aircraft designed and developed by Lycoming Engines in the 1930s. Although the engine was flown in an aircraft, it was not fitted to any aircraft selected for production. It later served as the basis for the Lycoming H-2470 engine.

Multi-cylinder engine

For multiple-cylinder steam engines, see Compound steam engine and Triple-expansion steam engine

A multi-cylinder engine is a reciprocating internal combustion engine with multiple cylinders. It can be either a 2-stroke or 4-stroke engine, and can be either Diesel or spark-ignition. The cylinders and the crankshaft which is driven by and co-ordinates the motion of the pistons can be configured in a wide variety of ways. Multi-cylinder engines offer a number of advantages over single-cylinder engines, chiefly with their ability to neutralize imbalances by having corresponding mechanisms moving in opposing directions during the operation of the engine.A multiple-cylinder engine is also capable of delivering higher revolutions per minute (RPM) than a single-cylinder engine of equal displacement. This is true for two reasons. First of all, the stroke of the pistons is reduced. This decreases the distance necessary for a piston to travel back and forth per each rotation of the crankshaft, and thus limiting the piston speed for a given RPM. Secondly, in an engine with multiple cylinders, the piston mass is reduced. This reduces stress on internal components at higher RPM's. Typically, the more cylinders an engine has, the higher the RPM's it can attain for a given displacement and technology level, at a cost of increased friction losses and complexity. Peak torque is also reduced, but the total horsepower is increased due to the higher RPM's attained.

Although there are 1, 3 and 5-cylinder engines, almost all other inline engines are built with even numbers of cylinders, as it is easier to balance out the mechanical vibrations. Another form of multiple-cylinder internal combustion engine is the radial engine, with cylinders arranged in a star pattern around a central crankshaft. Radial engines are most commonly used as aircraft engines, and in basic single-row configuration are built with odd numbers of cylinders (from 3 to 9). An odd number of cylinders is necessary in a four stroke radial, since the firing order is such that every other cylinder fires as the crankshaft rotates. Only with an odd number of cylinders will all cylinders evenly fire in this manner in two crankshaft revolutions (first the odd cylinders, followed by the even cylinders). "Twin-row" or "multi-row" radials are also built, which is basically two or more single-row radials connected front-to-back and driving a common crankshaft. In this "twin row", or "multi-row" configuration, the total number of cylinders will be an even number, although each row still has an odd number. For example, a typical single row radial such as the Wright Cyclone has 9 cylinders. The twin row Wright Twin Cyclone is based on this engine and thus has two banks of 9 cylinders, for a total of 18, an even number.

PZL-104 Wilga

PZL-104 Wilga (golden oriole) is a Polish short-takeoff-and-landing (STOL) civil aviation utility aircraft designed and originally manufactured by PZL Warszawa-Okęcie, and later by European Aeronautic Defence and Space Company (EADS), who had acquired the original manufacturer during 2001.

First flown on 24 April 1962 and entering service during the following year, the Wilga has evolved through many ever-improving versions during its continuous production from 1962 to 2006. The type was largely used by civil operators; those military air services that did fly the type typically used it as a trainer and liaison aircraft. In excess of 1,000 aircraft were produced prior to European Aeronautic Defence and Space Company (EADS) announced on their website that production of the Wilga would cease in 2006.

PZL-105 Flaming

The PZL-105 Flaming (flamingo) is a Polish short-takeoff-and-landing (STOL) utility aircraft designed by PZL "Warszawa-Okęcie". It remained a prototype.


PZL M-2 was a Polish trainer aircraft prototype of 1958, a low-wing monoplane with a fixed gear, designed at WSK-Mielec, that did not enter production.

Porsche in motorsport

Porsche has been successful in many branches of motorsport of which most have been in long distance races.

Despite their early involvement in motorsports being limited to supplying relatively small engines to racing underdogs up until the late 1960s, by the mid-1950s Porsche had already tasted moderate success in the realm of sports car racing, most notably in the Carrera Panamericana and Targa Florio, classic races which were later used in the naming of street cars. The Porsche 917 of 1969 turned them into a power house, winning in 1970 the first of over a dozen 24 Hours of Le Mans, more than any other company. With the 911 Carrera RS and the Porsche 935 Turbo, Porsche dominated the 1970s, and even has beaten sports prototypes, a category in which Porsche entered the successful 936, 956 and 962 models.

Porsche is currently the world's largest race car manufacturer. In 2006, Porsche built 195 race cars for various international motor sports events, and in 2007 Porsche is expected to construct no less than 275 dedicated race cars (7 RS Spyder LMP2 prototypes, 37 GT2 spec 911 GT3-RSRs, and 231 911 GT3 Cup vehicles).Porsche regards racing as an essential part of ongoing engineering development—it was traditionally very rare for factory-entered Porsche racing cars to appear at consecutive races in the same specification. Some aspect of the car almost invariably, was being developed, whether for the future race programs or as proof of concept for future road cars.

Puch 500

Puch 500 was a city car produced by the Austrian manufacturer Puch, a subsidiary of Steyr-Daimler-Puch in Graz. It was built under licence from Fiat and was based on the Fiat 500.

Rear-engine, front-wheel-drive layout

A rear-engine, front-wheel-drive layout is one in which the engine is between or behind the rear wheels, and drives the front wheels via a driveshaft, the complete reverse of a conventional front-engine, rear-wheel-drive vehicle layout.

The earliest example of the form appeared in 1932, with the design and construction of the prototype Maroon Car by chief designer Harleigh Holmes at Coleman Motors, an established builder of Front- and All-Wheel-Drive vehicles based in Littleton, Colorado. The car had front-wheel drive and was powered by a rear-mounted V-8 engine. Only one was built and the vehicle was never placed in production.Since then, it has remained an extremely uncommon drive layout throughout automotive history, used only by a few prototypes and concept cars, such as the 1937 "Howie-Wiley Machine Gun Carrier" (nicknamed "Belly-Flopper"), Buckminster Fuller’s 1933 Dymaxion car, which was able to turn within its wheelbase thanks to rear-wheel steering, and the 1947 Gregory Sedan.The layout has occasionally seen renewed interest as a potential option for innovative car designs, such as in the 1999 patent application of inventor–engineer Michael Basnett at the former Rover Group, which proposed a front transaxle, rear quasi-flat engine (an inline-4, turned 90 degrees) architecture, with the fuel tank placed where the right-hand cylinder bank would have been in a "true" flat engine; overall somewhat mimicking the "pancake engine" design of the Volkswagen Type 3 but in water-cooled form and without rear drive.

According to the patent, the layout is designed to be advantageous in terms of crash performance by increasing the front crumple zone, in allowing greater styling freedom, in enhanced ride via reduced noise, vibration, and harshness, and in lowered center of gravity providing improved handling, braking and roll characteristics - as well as, much like the Type 3, increased cabin and cargo space within the same chassis footprint and body height. Its main disadvantage is the lack of weight over the drive wheels, particularly under hard acceleration as weight shifts to the rear.

However, as mentioned in a Jalopnik article listing all known RF-layout cars, it too appears to have been nothing more than a speculative exercise, without so much as a single physical prototype being built—and the point of whether Rover Group intended to develop it any further is moot, as the corporation was broken up and its assets sold off barely a year later, with the fate of that particular piece of IP being unclear.

The drivetrain design closest to RF in actual series production vehicles is the Mid-engine, four-wheel-drive layout, typically seen in high end sportscar designs, and which, with the use of power-split centre differentials or hybrid drive systems, can be set up to send a variable amount of the total drive to the front wheels, in some cases up to 100%. Electric front-wheel-drive vehicles can also be found with small range-extender motor-generators, which are typically mounted in the rear luggage compartment, but do not technically count as RF drivetrain as there is no direct mechanical link between engine and wheels, or even the generated engine power and drive motor output, as the generator tends to run at a constant speed and is used to maintain battery charge rather than power the motor directly.

Symmetrical All Wheel Drive

Symmetrical All Wheel Drive (also known as Symmetrical AWD or SAWD) is a full-time four wheel drive system developed by Japanese automobile manufacturer Subaru. The SAWD system consists of a longitudinally mounted boxer engine coupled to a symmetrical drivetrain with equal length half-axles. The combination of the symmetrical layout with a flat engine and transmission balanced over the front axle provides optimum weight distribution with a low center of gravity, improving car handling characteristics. Since 1996, most international market Subaru vehicles include SAWD as standard equipment, with the rear wheel drive BRZ and kei cars as the exceptions.

V engine

A V engine, or Vee engine is a common configuration for an internal combustion engine. The cylinders and pistons are aligned, in two separate planes or 'banks', so that they appear to be in a "V" when viewed along the axis of the crankshaft. The Vee configuration generally reduces the overall engine length, height and weight compared with an equivalent inline configuration.


Zündapp (a.k.a. Zuendapp) was a major German motorcycle manufacturer founded in 1917 in Nuremberg by Fritz Neumeyer, together with the Friedrich Krupp AG and the machine tool manufacturer Thiel under the name "Zünder- und Apparatebau G.m.b.H." as a producer of detonators (Zünder- und Apparatebau is German for Igniter and Apparatus). In 1919, as the demand for weapons parts declined after World War I, Neumeyer became the sole proprietor of the company, and two years later he diversified into the construction of motorcycles.

Following World War II, Zündapp expanded into the microcar, moped and scooter markets. The company collapsed in 1984.

Stroke cycles
& number of cylinders
Car design
Body styles
Specialized vehicles
Drive wheels
Engine position
Layout (engine / drive)
Engine configuration
(internal combustion)


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