Compared to V-twins and flat-twins, straight-twins are more compact and usually cheaper to make, but may generate more vibration during operation. Straight-twin engines have been used in motorcycles, but are used in automobiles. Automobiles with straight-twin engines are very small and include city cars. Recent examples of cars with straight-twin engines include the Tata Nano, powersports applications include use in outboard motors, personal water craft, all-terrain vehicles and ultralight aircraft. Different crankshaft angles are used in four-stroke straight-twins to achieve different characteristics of firing intervals and engine balance, affecting vibrations, the traditional British parallel twin had 360° crankshafts, while some larger Japanese twins of the 1960s adopted the 180° crankshaft. In the 1990s, new engines appeared with a 270° crankshaft, straight-twins have the advantage of being more compact, relatively simple, and cheaper to make in comparison to V- or flat-twins. They may be prone to vibration, either because of the irregular firing interval present in 180° crank engines or the large uncountered reciprocating mass in 360° crank engines, inline-twins suffer further from torsional torque reactions and vibration.
Unlike V-twins, straight-twin engines do not use a crank pin for both connecting rods, each cylinder has its own crank pin. Honda straight-twin engines, which began appearing in the late 1950s, had four main bearings, subsequent engines had four or occasionally three main bearings, ball bearings being better than shell bearings for this engine configuration. In motorcycles, as cars and other vehicles, the terms parallel-twin, vertical-twin and inline-twin are used. The term parallel twin has used to refer specifically to a four-stroke straight-two engine with 360° crankshaft causing the pistons to travel parallel to each other. Other times, parallel-twin, inline-twin and the variants have been used interchangeably. The first production motorcycle using a motor was the Hildebrand & Wolfmuller of 1894. Its cylinders lay flat and forward-facing, its pistons connected directly to the wheel with a locomotive-style connecting rod. Approximately 2000 were produced through 1897, the second production motorcycle to use a straight twin design, this time a parallel twin with vertical cylinders akin to the British type, was the Werner of 1903.
It used cast-iron cylinders with integral heads, and side valves, the most famous example of the straight-twin engine was produced by Triumph from 1937 onwards, the 5T Speed Twin. Experiments with this type began as designer Edward Turner and his supervisor. From the experiments, it was shown that a 360° crank angle was better suited to the use of a single carburettor than a 180° crank angle
Weber is an Italian company which produced carburetors, it is owned by Magneti Marelli Powertrain S. p. A. which is in turn part of the Fiat Group. Carburetor production in Italy ended in 1992, although Weber carburetor production was shifted to Madrid, edoardo Weber began his automotive career working for Fiat, first at their Turin plant and at a dealership in Bologna. After the war, with prices high, he reached a certain success in selling conversion kits for running trucks on kerosene instead. The company was established as Fabbrica Italiana Carburatori Weber in 1923 when Weber produced carburetors as part of a kit for Fiats. Weber pioneered the use of two-stage twin barrel carburetors, with two venturis of different sizes, the one for low speed running and the larger one optimised for high speed use. In the 1930s Weber began producing twin-barrel carburetors for motor racing where two barrels of the size were used. These were arranged so that each cylinder of the engine has its own carburetor barrel and these carburetors found use in Maserati and Alfa Romeo racing cars.
Twin updraught Webers fed superchargers on the 1938 Alfa Romeo 8C competition vehicles, after Webers death in 1945, Fiat finally assumed control of the company in 1952. In 1986, Fiat took control of Webers competitor Solex and this was reorganized as Magneti Marelli Powertrain S. p. A. in 2001. Genuine Weber carburetors were produced in Bologna, Italy up until 1992, when production was transferred to Madrid, Weber Carburetors are sold for both street and off-road use, with the twin choke sidedraught DCOE being the most common one. They are sold in what is referred to as a Weber Conversion kit, in modern times, fuel injection has replaced carburetors in both production cars and most modern motor racing, although Weber carburetors are still used extensively in classic and historic racing. They are supplied as high quality replacements for problematic OEM carburetors, Weber fuel system components are distributed by Magneti Marelli, Webcon UK Ltd. and, in North America, by several organizations, including Worldpac, marketing under the Redline name.
Other suppliers include Overseas Distributing and Pierce Manifolds, Weber carburetors are marked with a model code on the mounting flange, the body, or on the cover of the float-chamber. This begins with a number which originally indicated the diameter of the throttle bore, after the letters there will be a further number, which may be followed by a letter, e. g. 4B, 13A, these indicate the series. The full designation might be 40 DCOE29,45 DCOE9, etc
By using split crankpins or ignoring minor vibrations, any V angle is possible. The 180° configuration is referred to as a flat-twelve engine or a boxer although it is in reality a 180° V since the pistons can. This is not important in a car if all-out performance is the only goal. Since cost and fuel economy are usually important even in luxury and racing cars and it is often used in marine engines where great power is required, and the hull width is limited, but a longer vessel allows faster hull speed. In twin-propeller boats, two V12 engines can be enough to sit side-by-side, while three V12 engines are sometimes used in high-speed three-propeller configurations. Large, fast cruise ships can have six or more V12 engines, after World War II, the compact, more powerful, and vibration-free turboprop and turbojet engines replaced the V12 in aircraft applications. The first V-type engine was built in 1889 by Daimler, to a design by Wilhelm Maybach, by 1903 V8 engines were being produced for motor boat racing by the Société Antoinette to designs by Léon Levavasseur, building on experience gained with in-line four-cylinder engines.
In 1904, the Putney Motor Works completed a new V12 marine racing engine—the first V12 engine produced for any purpose, a single camshaft mounted in the central V operated the valves directly. As in many engines, the camshaft could be slid longitudinally to engage a second set of cams. Starting is by pumping a charge into each cylinder and switching on the trembler coils, a sliding camshaft gave direct reversing. The camshaft has fluted webs and main bearings in graduated thickness from the largest at the flywheel end, displacing 1,120 cu in, the engine weighed 950 pounds and developed 150 bhp. Little is known of the achievements in the 40-foot hull for which it was intended. One V12 Dörwald marine engine was still running in a Hong Kong junk in the late-1960s. Two more V12s appeared in the 1909-1910 motor boat racing season, the Lamb Boat & Engine Company of Clinton, Iowa built a 1,559 cu in engine for the companys 32-foot Lamb IV. It weighed in at 2,114 pounds, no weight is known for the massive 3,464 cu in F-head engine built by the Orleans Motor Company.
Output is quoted as nearly 400 bhp, by 1914, when Panhard built two 2,356 cu in engines with four-valve cylinder heads the V12 was well established in motor boat racing. In October 1913, Louis Coatalen, chief engineer of the Sunbeam Motor Car Company entered a V12 powered car in the Brooklands short, the engine displaced 9 L, 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
In automotive engineering a multi-valve or multivalve engine is one where each cylinder has more than two valves. A multi-valve engine has better breathing and may be able to operate at higher revolutions per minute than a two-valve engine, a multi-valve engine design typically has three, four, or five valves per cylinder to achieve improved performance. Any four-stroke internal combustion engine needs at least two valves per cylinder, one for intake of air and fuel, and another for exhaust of combustion gases. Adding more valves increases valve area and improves the flow of intake and exhaust gases, thereby enhancing combustion, volumetric efficiency, multi-valve geometry allows the spark plug to be ideally located within the combustion chamber for optimal flame propagation. Multi-valve engines tend to have smaller valves that have lower reciprocating mass, which can wear on each cam lobe. Some engines are designed to each intake valve at a slightly different time. More valves provide additional cooling to the cylinder head, the disadvantages of multi-valve engines are an increase in manufacturing cost and a potential increase in oil consumption due to the greater number of valve stem seals.
Some SOHC multi-valve engines use a single fork-shaped rocker arm to drive two valves so that fewer cam lobes will be needed in order to reduce manufacturing costs, three-valve cylinder head This has a single large exhaust valve and two smaller intake valves. A three-valve layout allows better breathing than a head. The manufacturing cost for this design can be lower than for a four-valve design, the three-valve design was common in the late 1980s and early 1990s, and from 2004 the main valve arrangement used in Ford F-Series trucks, and Ford SUVs. Four-valve cylinder head This is the most common type of multi-valve head and this design allows similar breathing as compared to a three-valve head, and as the small exhaust valves allow high RPM, this design is very suitable for high power outputs. Five-valve cylinder head Less common is the head, with two exhaust valves and three inlet valves. All five valves are similar in size and this design allows excellent breathing, and, as every valve is small, high RPM and very high power outputs are theoretically available.
After making five-valve Genesis engines for several years, Yamaha has reverted to the cheaper four-valve design, beyond five valves For a cylindrical bore and equal-area sized valves, increasing the number of valves beyond five decreases the total valve area. The following table shows the areas of differing valve quantities as proportion of cylinder bore. These percentages are based on geometry and do not take into account orifices for spark plugs or injectors. Also, in practice, exhaust valves are larger than intake in heads with an even number of valves-per-cylinder. The same applies to variable valve timing and variable intake manifolds, rotary valves offer improved engine breathing and high rev performance but these were never very successful
Compared to OHV pushrod systems with the same number of valves, the reciprocating components of the OHC system are fewer and have a lower overall mass. Though the system drives the camshafts may be more complex, most engine manufacturers accept that added complexity as a trade-off for better engine performance. The fundamental reason for the OHC valvetrain is that it offers an increase in the ability to exchange induction. Another performance advantage is gained as a result of the better optimised port configurations made possible with overhead camshaft designs, with no intrusive pushrods, the overhead camshaft cylinder head design can use straighter ports of more advantageous cross-section and length. The OHC design allows for higher speeds than comparable cam-in-block designs. The higher engine speeds thus allowed increases power output for a given torque output, in earlier OHC systems, including inter-war Morrises and Wolseleys, oil leaks in the lubrication systems were an issue. Single overhead camshaft is a design in which one camshaft is placed within the cylinder head, in the SOHC design, the camshaft operates the valves directly, traditionally via a bucket tappet, or via an intermediary rocker arm. SOHC cylinder heads are less expensive to manufacture than double overhead camshaft cylinder heads.
Timing belt replacement can be easier since there are fewer camshaft drive sprockets that need to be aligned during the replacement procedure, SOHC designs offer reduced complexity compared to overhead valve designs — when used for multivalve cylinder heads, in which each cylinder has more than two valves. Exhaust and inlet manifolds were both on the side of the engine block. This did, offer excellent access to the spark plugs, in the early 1980s, Toyota and Volkswagen Group used a directly actuated, SOHC parallel valve configuration with two valves for each cylinder. The Toyota system used hydraulic tappets, the Volkswagen system used bucket tappets with shims for valve clearance adjustment. Honda used a similar system in their motorcycles, using the term Unicam for the concept. This system uses one camshaft for each bank of cylinder heads, with the cams operating directly onto the valve and indirectly, through a short rocker arm. This allows a compact, light valvetrain to operate valves in a combustion chamber.
The Unicam valve train was first used in single cylinder dirt bikes, a dual overhead camshaft valvetrain layout is characterised by two camshafts located within the cylinder head, one operating the intake valves and the other one operating the exhaust valves. This design reduces valvetrain inertia more than is the case with a SOHC engine, a DOHC design permits a wider angle between intake and exhaust valves than do SOHC engines. This can allow for a less restricted airflow at higher engine speeds, DOHC with a multivalve design allows for the optimum placement of the spark plug which, in turn, improves combustion efficiency
Ferrari Tipo 500
The Ferrari 500 was a Formula 2 racing car designed by Aurelio Lampredi and used by Ferrari in 1952 and 1953, when the World Championship was run to F2 regulations. Ferrari were the team to have a car specifically designed for the new formula. The car was powered by an inline engine which was mounted behind the front axle. Alberto Ascari used the car to win his first world championship, winning all, the race he missed was because he was driving the 4. 5-litre Ferrari at the Indianapolis 500, however Ferrari won the race he was absent from as well. Ascari won seven consecutive World Championship races in the 500, a record which stood until Sebastian Vettel broke it in 2013, if the 1953 Indianapolis 500 is discounted, the run is extended to nine. Despite two new models appearing during this period the 625 was not completely replaced until 1956 when Ferrari began using the D50 chassis Ferrari purchased along with the Lancia Formula One team,1 – The Constructors World Championship did not exist before 1958
1955 Le Mans disaster
The 1955 Le Mans disaster occurred during the 24 Hours of Le Mans motor race in Le Mans, France on 11 June 1955, when a major crash caused large fragments of debris to fly into the crowd. To reach his pit-stop, Mike Hawthorn had to cut in front of Lance Macklin, the collision propelled Levegh’s car upwards and into an earthen embankment and throwing the driver out, killing him. The momentum of the components of the car carried them into the packed grandstand with terrible effect. There was much debate over the apportioning of blame, the official inquiry held none of the drivers specifically responsible, and criticised the layout of the 30-year old track, which had not been designed for cars of this speed. There was great anticipation for the race for a showdown between Ferrari and Mercedes-Benz, all of whom had won the race recently and who all arrived with new improved cars. The Ferraris, current champions, were very fast but fragile, Jaguar concentrated their racing almost exclusively on Le Mans and had a very experienced driver line-up including erstwhile F1 Ferrari driver Mike Hawthorn.
After conquering Formula 1, Mercedes-Benz had debuted its new 300 SLR in that year’s World Championship, the 300 SLR featured a body made of an ultralightweight magnesium alloy called Elektron. It had been Leveghs epic solo drive in the 1952 race which failed in the last hour, safety measures commonly in place today were relatively unknown in 1955. By 1955 top speeds for the cars were in excess of 270 kph. That said, the circuit had been resurfaced and widened post-war, similarly the pits and grandstands had been reconstructed, although there were no barriers between the pit lane and the racing line, and only a 4’ earthen bank between the track and the spectators. The cars had no seatbelts, the reasoning that it was preferable to be thrown clear in a collision rather than be crushed or trapped in a burning car. The other team cars were being kept on leashes to conserve the cars. It was 6. 26pm, at the end of lap 35 when the leading cars’ first pit stops were starting, on lap 35 Hawthorn and Fangio were racing as hard as ever.
In his biography, Hawthorn said he was mesmerized by the legend of the Mercedes superiority. Then I came to my senses and thought ‘Damn it, why should a German car beat a British car. ’” The lap before Hawthorn’s pit crew had signaled for him to come in the next lap. He had just lapped ”Levegh” after Arnage and was determined to keep Fangio at bay as long as possible, coming out of Maison Blanche he rapidly caught Lance Macklin in his Austin Healey 100S, who had seen him and pulled over to the right to let him pass. Putting another lap on Macklin coming up to the main straight Hawthorn raised his hand to indicate he was pitting and pulled across to the right. What caught Macklin out though was that Hawthorn, using his advanced disc brakes, who himself braked hard, ran off the right-hand edge of the track, throwing up dust
Ferrari Dino engine
The Ferrari Dino engine is a line of mechanically similar V6 and V8 engines produced by Ferrari for the past 40 years Alfredo Dino Ferrari, was the son of Enzo Ferrari. Dino suggested to Enzo Ferrari the development of a V6 engine for F2 at the end of 1955, soon afterwards, Alfredo fell ill, suffering from muscular dystrophy. While in hospital, he discussed technical details with the engineer Vittorio Jano, Dino would never see the engine, he died on June 30,1956 at the age of 24. The Dino V6 was Ferraris first V6 engine, the Dino V8 engine was introduced later. The V8 engines all used a crankshaft configuration. The production Dino V6 began as a discussion between Vittorio Jano and Enzo and Dino Ferrari about the ideal 1.5 L engine for use in the 1958 Formula Two auto racing series. Jano, formerly of Alfa Romeo and Lancia, pressed for a conventional 60° V6 but the Ferraris were open-minded. Janos 60° design incorporated some of his ideas from the Lancia Aurelia, and were used in a number of Formula One, Formula Two, appearing in 1958, it used a 77x71 mm bore and stroke for 1984 cc and produced 200 hp in the 196 S.
Two larger versions were produced, the 245 hp 2497 cc 246 S and 296 hp 2962 cc 296 S. These engines continued in the 1962196 SP and 286 SP, the latter had a 90 mm bore and 75 mm stroke for 2863 cc and 260 hp. This engine was so small that very little room was available for smooth intake tracts, the Ferraris were convinced that a freer-flowing intake could result in more power, so a new design was called for. Ferrari designers began work on the first Dino V6 engine in 1956 and this engine was installed in the Ferrari 156 F2 car and was first raced in the Grand Prix of Naples in April 1957, where it finished in third place behind two Lancia-Ferrari V8 Formula One cars. The result of the creativity was the worlds only 65° V6 engine. The extra 5° between cylinder banks gave Ferrari the straight intakes he wanted, as this engine was not a true V6 but had a separate crank pin for every connecting rod, the crank pins were offset by 55 degrees within every pair of cylinders. This ensured an even firing order for the engine as well as an even distance between firing pulses per cylinder bank.
Thus the engine was as smoothly running as a conventional 60 degree V6, although the Dino V6 was discontinued with the introduction of the V8, the 65° design continues to this day, It reappeared on Ferraris 1992456 V12. The 85x71 mm 2417 cc engine used in the 246 S/I produced 280 hp with dual overhead camshafts pushing two valves per cylinder, the mid-engined 1961246 SP used this same engine, as did the 156 F1. The 65° Dino V6 quickly replaced the 60° unit in racing, Ferrari needed to have the engine in 500 production vehicles to homologate it for racing use
Aurelio Lampredi was an Italian automobile and aircraft engine designer. Born in Livorno, he began his career at Piaggio, makers of the Vespa scooter and he worked at Isotta Fraschini before World War II, and joined Reggiane to design aircraft engines. Lampredis fame brought him to Ferrari in 1946 where he designed large 3.3,4.1 and 4.5 L versions of its V12 which first saw use in the 1950s 275S,340 F1 and 375 F1 race cars. Lampredi returned to Isotta Fraschini in March 1947 but returned to Ferrari at the beginning of 1948, Lampredis engines were used as large naturally aspirated alternatives to the diminutive Gioacchino Colombo-designed V12s used in most Ferrari cars until that time. Especially after the failure of Colombos supercharged engine in Formula One, Lampredi oversaw Ferraris racing effort during its early success in 1952 and 1953. Lampredis work at Ferrari ended permanently in 1955 when Ferrari bought Lancias racing team and famed engine designer Vittorio Jano, though Lampredis engine designs lived on in Ferrari road cars, Janos V6 and V8 engines quickly replaced Lampredis large V12s for racing use.
After Ferrari, Lampredi went to Fiat, where he oversaw that companys engine design efforts until 1977 and it was at Fiat where he designed the Fiat Twin-Cam and SOHC engines, which provided motive-force for most Fiat automobiles for over 32 years. He was manager of Fiats Abarth factory racing group from 1973 through 1982. He was responsible for designing the engine that allowed Fiat to allocate in the Brazilian market in 1976 and that engine equipped the Fiat 147, direct derivation of the European Fiat 127 but exclusively Brazilian. That was a big impact for the Brazilian automotive industry, because the Fiat 147 was the first national vehicle to have transverse mounted engine with belt driven overhead camshaft and it was the first engine made on a large scale to be powered by Ethanol. Then, in 1979 the Fiat 147 is known to be the worlds first car sold on a scale to be moved by Ethanol. Lampredi died in Livorno in 1989
The Mulsanne Straight is the name used in English for a formerly 6 km long straight of the Circuit des 24 Heures around which the 24 Hours of Le Mans auto race takes place. Since 1990, the straight is interrupted by two chicanes, with the last section, that includes a kink and a hump, leading to the corner near the village of Mulsanne. When race meetings are not taking place the Mulsanne Straight is part of the road system of France. It is called Ligne Droite des Hunaudières, a part of the route départementale D338, the Hunaudières leads to the village of Mulsanne which is the reason for its English name. After exiting the Tertre Rouge corner, cars would spend almost half of the lap at full throttle, the Porsche 917 long tail, used from 1969 to 1971, had reached 362 km/h. After engine size was limited, the top speed dropped until powerful turbo engines were allowed, speeds on the straight by the Group C prototypes reached over 400 km/h during the late 1980s. One driver had a lucky escape in 1986.
British driver Win Percy had a tyre on his V12 powered Jaguar XJR-6 explode at some 386 km/h, tearing off the rear bodywork, the wreckage finally came to a halt 600 m down the road. However, despite almost obliterating the vehicle, Percy somehow walked away from the crash with nothing more than a badly battered helmet, the chicanes were added because the FIA decreed it would no longer sanction a circuit which had a straight longer than 2 kilometres. Which is roughly the length of the Döttinger Höhe straight at the Nürburgring Nordschleife, however, in 1990 the viewing experience obtained at both restaurants was diminished with the introduction of the chicanes. The Bentley Mulsanne and Bentley Arnage are named after the corners, ACO, The legendary spots on the circuit, The Mulsanne Straight,24 Hours of Le Mans, retrieved 25 July 2015 Fuller, Michael J
World Sportscar Championship
The World Sportscar Championship was the world series run for sports car racing by the FIA from 1953 to 1992. The official name of the series changed throughout the years, however it has generally been known as the World Sportscar Championship from its inception in 1953. The World Sportscar Championship was, with the Formula One World Championship, in 2012 the World Sportscar Championship was revived and renamed as the World Endurance Championship. Cars were split into Sports Car and GT categories and were divided into engine displacement classes. The Ferrari and Maserati works teams were fierce competitors throughout much of the decade, notably absent from the overall results were the Jaguar works team, who did not enter any events other than Le Mans, despite the potential of the C- and D-Types. In 1962, the calendar was expanded to include smaller races, the World Sportscar Championship title was discontinued, being replaced by the International Championship for GT Manufacturers. They group cars into three categories with specific sizes, less than one litre, less than two litres, and over two litres.
Hillclimbs, sprint races and smaller races expanded the championship, which now had about 15 races per season, for 1963 the three engine capacity classes remained but a prototype category was added. For 1965 the engine classes became for cars under 1300 cc, under 2000 cc, in 1972 the Group 6 Prototype and Group 5 Sports Car classes were both replaced by a new Group 5 Sports Car class. These cars were limited to 3.0 L engines by the FIA, the new Group 5 Sports Cars, together with Group 4 Grand Touring Cars, would contest the FIAs newly renamed World Championship for Makes from 1972 to 1975. Prototypes returned in 1976 as Group 6 cars with their own series, the World Championship for Sports Cars, in 1981, the FIA instituted a drivers championship. While this change was unwelcome amongst some of the private teams, several of the old guard manufacturers returned to the WSC within the next two years, with each marque adding to the diversity of the series. Under the new rules, it was possible for normally aspirated engines to compete with the forced induction engines that had dominated the series in the 70s.
In addition, most races ran for either 500 or 1000 km, Group B cars, which was a GT class, were allowed to race, but entries in this class were sparse, and Group B cars disappeared from the series, with sports-prototypes dominating the championship. Porsche was the first constructor to join the series, with the 956, as costs increased, a C2 class was created for privateer teams and small manufacturers, with greater limits to fuel consumption. In this lower class, most cars used either the BMW M1 engine or the new Cosworth DFL, like in the main class, Tiga and Ecurie Ecosse were among the most competitive in this class. While the Group C formula had brought back to the sport. For 1986, the World Endurance Championship became the World Sports-Prototype Championship, the new classification, known as Group C Category 1, was designed to mandate Formula One engines
The straight-six engine or inline-six engine is an internal combustion engine with the cylinders mounted in a straight line along the crankcase with all the pistons driving a common crankshaft. The bank of cylinders may be oriented at any angle, and where the bank is inclined to the vertical, the straight-six layout is the simplest engine layout that possesses both primary and secondary mechanical engine balance, resulting in much less vibration than engines with fewer cylinders. In automobiles, the design is used for engine displacements ranging from approximately 2 to 5 litres. It is used for smaller engines but these, although very smooth running. Since the length of an engine is proportional to the number of cylinders in one bank. Pre-World War II engines could be large by modern standards — such as the Rolls Royce Silver Ghosts 7.4 L engine and the 824 cu in of the 1910s Peerless, Pierce. They were used in a variety of including the de Havilland Dragon Rapide. The largest are used to ships, and use fuel oil.
The straight-six can be viewed as a modular component of larger motors which stack several straight-sixes together, e. g. flat- or V-12s, W-18s. Straight-six engines were introduced earlier than V6 engines. While the first straight-six was manufactured in 1903 by Spyker, it was not until 1950 that a production V6 was introduced, V6s had intrinsic vibration problems not present in the straight-six. The poor secondary harmonic balance of four-cylinder engines is largely addressed with the use of balance shafts although it can never match the in-line six, TVR used a straight-six configuration exclusively in their final cars before their demise. In a reversal of trends, Mercedes-Benz announced a return to inline-6 engines in October 2016. This was a part of a trend toward higher efficiency engines with fewer cylinders, manufacturers began to replace V8 engines with straight-6 engines and V6 engines with straight-4 engines, while V8 engines became smaller. Straight-sixes continue to be used in medium to large trucks, Ford is one notable exception using a V8 in medium duty trucks.
GM pickup trucks abandoned the straight-six in 1984 for the 4.3 V6, in 2002, General Motors introduced the Vortec 4200 as part of the modular straight-four, straight-five and straight-six GM Atlas engine line. It was used in their sport utility vehicles. Jeep abandoned the straight-six in 2006 with the 2006 Jeep Wrangler being the last vehicle, Ram Trucks continues to offer straight-six engines in its heavy duty pickup truck and chassis cab models, although only V6 and V8 engines are available in the smaller versions