A V6 engine is a six-cylinder piston engine where the cylinders share a common crankshaft and are arranged in a V configuration. The first V6 prototype engine was produced in 1906, however it took until 1950 for the first automotive V6 engine to reach production. In the past 20 to 30 years, the V6 layout has become the most common layout for six-cylinder automotive engines. Due to their short length, V6 engines are used as the larger engine option for vehicles which are otherwise produced with inline-four engines in transverse engine vehicles. A downside for luxury cars is; some sports cars use flat-six engines instead of V6 engines, due to their lower centre of gravity. The displacement of modern V6 engines is between 2.5 to 3.5 L, though larger and smaller examples have been produced, such as the 1.8 L V6 engines used in the 1991-1998 Mazda MX3, the 1999-2005 Rover 45. All V6 engines— regardless of the V-angle between the cylinder banks— are subject to a primary imbalance caused by each bank consisting of an inline-three engine, due to the odd number of cylinders in each bank.
Straight-six engines and flat-six engines do not experience this imbalance. To reduce the vibrations caused by this imbalance, some V6 engines use counterweights on the crankshaft and/or a counter-rotating balance shaft. Six-cylinder designs have less pulsation in the power delivery than four-cylinder engines, due to the overlap in the power strokes of the six-cylinder engine. In a four-cylinder engine, only one piston is on a power stroke at any given time; each piston comes to a complete stop and reverses direction before the next one starts its power stroke, which results in a gap between power strokes and annoying harshness at lower engine speeds. In a six-cylinder engine with an firing interval, the next piston starts its power stroke 60° before the previous one finishes, which results in smoother delivery of power to the flywheel. Comparing engines on a dynamometer, a V6 engine shows instantaneous torque peaks of 150% above mean torque and valleys of 125% below mean torque, with a small amount of negative torque between power strokes.
In the case of a four-cylinder engine, the peaks are nearly 300% above mean torque and valleys of 200% below mean torque, with 100% negative torque being delivered between strokes. However, a V6 with an uneven firing interval shows large torque variations of 200% above and 175% below mean torque. From 1991-present, Volkswagen has produced narrow angle VR6 engines with V-angles of 10.5 and 15 degrees. These engines use a single cylinder head shared by both banks of cylinders, in a design similar to the 1922-1976 Lancia V4 engine; the VR6 engines were used in transverse engine front-wheel drive cars which were designed for inline-four engines. Due to the minimal extra length and width of the VR6 engine, it could be fitted to the engine compartments easily, in order to provide a displacement increase of 50 percent. Since there is no room in the V between the cylinder banks for an intake system, all the intakes are on one side of the engine, all the exhausts are on the other side, it uses a firing order of 1-5-3-6-2-4, rather than the common V6 firing order of 1-2-3-4-5-6 or 1-6-5-4-3-2.
A V-angle of 60 degrees is the optimal configuration for V6 engines regarding engine balance. When individual crank pins are used for each cylinder, an firing interval of 120 degrees can be used; this firing interval is a multiple of the 60 degree V-angle, therefore the combustion forces can be balanced through use of the appropriate firing order. The inline-three engine that forms each cylinder bank, produces unbalanced rotating and reciprocal forces; these forces remain unbalanced in all V6 engines leading to the use of a balance shaft to reduce the vibration. The 1950 Lancia V6 engine was pioneering in its use of a six-throw crankshaft in order to reduce vibration. More recent designs use a three-throw crankshaft with'flying arms' between the crankpins; the flying arms allow an firing interval of 120 degrees to be achieved, used as balancing masses for the crankshaft. Combined with a pair of heavy counterweights on the crankshaft ends, flying arms can eliminate the primary imbalance and reduce the vibration from the secondary imbalance to acceptable levels.
The engine mounts can be designed to absorb these remaining vibrations. A 60 degree V-angle results in a narrower engine overall than V6 engines with larger V-angles; this angle results in the overall engine size being a cube shape, making the engine easier to fit either longitudinally or transversely in the engine compartment. Many manufacturers American ones, built V6 engines with a V-angle of 90 degrees based on their existing 90-degree V8 engines; such configurations were easy to design by removing two cylinders and replacing the V8 engine's four-throw crankshaft with a three-throw crankshaft. This reduced design costs, allowed the new V6 to share components with the V8 engine, sometimes allowed manufacturers to build the V6 and V8 engines on the same production line; the downsides of a 90 degree design are a wider engine, more vibration-prone than a 60 degree V6. The initial 90 degree V6 engines had three shared crankpins arranged at 120 degrees from each other, due to their origins from the V8 engines.
This resulted in an uneven firing order, with half of the cylinders using a firing interval of 90 degrees and other half using an interval of 150 degrees. The uneven firing intervals resulted in rough-
Brood XIX is the largest brood of 13-year periodical cicadas, last seen in 2011 across a wide stretch of the southeastern United States. Periodical cicadas are referred to as "17-year locusts" because most of the known distinct broods have a 17-year life cycle. Brood XIX is one of only three surviving broods with a 13-year cycle, it is notable because it includes four different 13-year species, one of, discovered in Brood XIX in 1998 by scientists listening to cicada songs. Every 13 years, Brood XIX tunnels en masse to the surface of the ground, lays eggs, dies off in several weeks. In 1907, entomologist C. L. Marlatt postulated the existence of 30 different broods of periodical cicadas: 17 distinct broods with a 17-year life cycle, to which he assigned Roman numerals I through XVII. Many of these hypothetical broods, have not been observed. Today only 15 are recognized. Brood XIX is one of three extant broods of 13-year cicadas; the other two are Broods XXIII, expected to re-emerge in 2027 and 2028 respectively.
A fourth 13-year brood, Brood XXI was last recorded in 1870 in the Florida panhandle, but is believed to be now extinct. Brood XIX includes all four different species of 13-year cicadas: Magicicada tredecim, Magicicada tredecassini, Magicicada tredecula, the discovered Magicicada neotredecim. 2011 is the first appearance of Brood XIX since the discovery of the new species, first observed in this brood in 1998 when scientists observed an unexpected peak of acoustical frequencies in the brood's song. The two species M. tredecim and M. neotredecim have an unusual geographical relationship in Brood XIX, with only a slight overlap between them, in a narrow band from northern Arkansas to southern Indiana. The other 13-year species occur together throughout the brood range, so in most parts of the range only three of the four species are present. All four 13-year species have distinct male calling songs, but the songs of M. tredecim and M. neotredecim in their narrow range of overlap show reproductive character displacement that makes them more distinct.
RCD is noticeable in Brood XIX. For Brood XIX in Alabama, adults of M. tredecula are less common than those of M. tredecim and M. tredecassini. Most maps of cicada distribution originate from 19th-century compilations that may show ranges much wider than those of current broods; the National Geographic Society is gathering reports from the public about the geographical distribution of Brood XIX as part of a larger project to remap the distribution of Magicicada. Older maps show occurrences of Brood XIX cicadas in Missouri, Louisiana, Tennessee, Indiana, North Carolina, South Carolina, GeorgiaAcross most of the range of Brood XIX, one observes M. tredecim in the southern regions and M. neotredecim in more northern ones, with some overlap in the westernmost region. In early May 2011, cicadas began emerging throughout an area enclosed by Georgia, Alabama, North Carolina and Tennessee; the next three appearances will be in 2024, 2037 and 2050. Clarinetist David Rothenberg performed with these cicadas, has performed with Brood II.
News reports of the cicadas' emergence in Illinois included links to a video showing holes in the ground left by larval emergence, an adult cicada breaking out of its larval shell, massed adult cicadas marching up tree trunks. By June 8, 2011, a North Carolina newspaper reported that adult cicadas, which live for about a month, were dying en masse. Nymphs from eggs that have been laid by Brood XIX females will emerge from the earth again in 2024, to restart the cycle. Magicicada Central More, Singing Insects of North America, University of Florida map Post, Susan L; the Trill of a Life Time, photographs by Michael R. Jeffords, The Illinois Steward, Spring 2004. Stannard, Jr. Lewis; the Distribution of Periodical Cicadas in Illinois, 1975. "Brood XIX, Cicada Mania "Magicicada Broods", Thomas, Singing Insects of North America, University of Florida map Post, Susan L. The Trill of a Life Time, photographs by Michael R. Jeffords, The Illinois Steward, Spring 2004. Video of emerging Brood XIX cicadas in Illinois, 2011 Video of Brood XIX cicadas responding to the saxophone playing of David Rothenberg
The Ford Fiesta Mk2 was the second generation of the Ford Fiesta supermini built by Ford Europe. Introduced in 1983, it was a mild facelift of the original car, it was available in 3-door hatchback and panel van styles, it was replaced by the updated Fiesta Mk3 for 1989. The Ford Fiesta Mk2 appeared in late August 1983, with interior; the engine compartment was wider, so as to accommodate a five-speed transmission and new engines. The front track accordingly increased by 33 mm, while the brakes and steering were altered; the steering was a modified version of the Escort's setup, while the front brakes were updated with the Escorts' front discs. At launch, the Mk2 Fiesta was only available with the familiar 957cc and 1117cc Kent Crossflow-based "Valencia" engine options, although they now featured variable venturi carburettors for improved fuel consumption; the more bulbous bonnet line of the Mk2 was created due to the need to package the taller Ford CVH engine, a 1.3 L version of which followed in 1984, this model featured a five-speed manual transmission for the first time.
The 1.0 was only offered with the four-speed at first, while the five-speed was available as an option in the 1.1. Two other versions of the Mk2 Fiesta appeared in 1984, it featured a 96 bhp 1.6 L CVH engine as seen in the Ford Escort XR3, a five-speed manual gearbox. There was a new 1.6 L diesel engined version of the Fiesta, making full advantage of the now wider engine compartment. Diesel power units in this market segment were still unusual, commentators found that the impressive fuel economy of the diesel powered Fiesta came at the expense of a power unit, noisy and rough. In West Germany, a market traditionally receptive to diesel powered passenger cars, the petrol/gasoline powered Fiesta was still outselling the diesel version by more than four to one in 1988; this may have been because the larger engine, shared with the Escort/Orion, offered only marginal fuel savings over that of the smallest petrol options and at a higher purchase price. When installed in the lighter Fiesta, this engine provided spritelier performance than in the Escort Diesel.
The Diesel Fiesta had altered spring settings at the rear and received the Sierra's MacPherson struts up front to deal with the heavier engine. The XR2's engine was replaced by a lean-burn variant in November 1986 which featured a revised cylinder head and carburettor. At this point the manufacturer took the opportunity to offer the 5-speed manual transmission standard on the 1.3 L model, as an option with the upgraded 1.1 L car. The 1.3–L CVH was replaced by a 1.4–L lean burn version of the same power unit for 1986, whilst the other engines were modified in order to use unleaded petrol. In February 1986 all models received the 40 litre fuel tank reserved for the XR2 model, increasing fuel capacity and range by 17%. In May 1987, Ford added the new CTX, incorporating continuously variable transmission, to the range, although it was only offered with the 1.1 engine, few of these Fiesta CTXs were produced. The Mk2 Fiesta, facing competition from the Vauxhall Nova and Austin Metro, was one of the UK's top superminis.
In its best-ever year, 1987, over 150,000 Fiesta models were sold in the UK, though it finished second in the sales charts to the Ford Escort. In West Germany Europe's largest national car market, the Fiesta managed to outsell the Volkswagen Polo in 1984, 1985 and again in 1989, while the Polo narrowly outsold the Fiesta each year between 1986 and 1988. Throughout this period, West German sales of the Opel Corsa trailed those of both the Fiesta and the Polo. By April 1989, when a new generation of Fiesta was launched, combined production and sales of the first two generations of Fiesta, produced between 1976 and 1989, had exceeded 4.5 million units. Oswald, Werner. Deutsche Autos 1945-1990, Band 3. Motorbuch Verlag, Stuttgart. ISBN 978-3-613-02116-7