Motorcycle testing and measurement
Motorcycle testing and measurement includes a range of more than two dozen statistics giving the specifications of the motorcycle, the actual performance, expressed by such things as the output of the engine, the top speed or acceleration of the motorcycle. Most parameters are uncontroversial and claims made by manufacturers are accepted without verification; these might include simple measurements like rake, trail, or wheelbase, or basic features, such as the type of brakes or ignition system. Other measurements are doubted or subject to misunderstandings, the motorcycling press serves as an independent check on sometimes unrealistic sales and marketing claims. Many of these numbers are subject to variable methods of measurements, or disagreement as to the definition of the statistic; the parameters most in contention for motorcycles are the weight, the engine output, the overall performance acceleration, top speed, fuel economy. With electric motorcycles and scooters, the range between charges is a pivotal measurement.
Motorcycle speed tests at high speeds, are prone to variation due to human error, limitations in equipment, atmospheric factors like wind and altitude. The published results of two otherwise identical tests could vary depending on whether the result is reported with or without industry standard correction factors calculated to compensate for test conditions. Rounding errors are possible as well when converting to/from kilometers per hour. With power being the product of force and speed, a motorcycle's power and torque ratings will be indicative of its performance. Reported numbers for power and torque may however vary from one source to another due to inconsistencies in how testing equipment is calibrated, the method of using that equipment, the conditions during the test, the location that force and speed are being measured at; the power of the engine alone called crankshaft power, or power at the crankshaft, will be greater than the power measured at the rear wheel. The amount of power lost due to friction in the transmission depends on the details of the design and construction.
Generalizing, a chain drive motorcycle may have some 5-20% less power at the rear wheel than at the crankshaft, while a shaft drive model may lose a little more than that due to greater friction. While the crankshaft power excludes these transmission losses, still the measurement is made elsewhere in the drive-train at the rear wheel. A correction for the transmission losses is applied to the measured values to obtain the crankshaft values. For motorcycles, the reported power and torque numbers pertain to the crankshaft. In directive 92/61/EEC of 30 June 1992 relating to the type-approval of two or three-wheel motor vehicles, it is referred to as "maximum engine power", manufacturers use similar terms; this convention may have come from the pre-unit construction, wherein the crankshaft was directly accessible for measurements, the gearbox might have come from a different manufacturer. However, when the engineering details of the transmission are known, the losses therein can be quantified & corrected for.
Explicit guidance on the homologation measurements and transmission corrections is given in directive 95/1/EC. A main source of ambiguity and differences comes from the conditions; these conditions include details like atmospheric conditions, tire pressure, but most importantly: the conditions of the motorcycle itself. Examples thereof are: was the alternator fitted?. One would hope that manufacturers would test their motorcycles in normal running order, so the condition that they are sold in, for which they obtained type-approval, but this is not always the case. Ducati, for instance, has chosen to publish more positive values, stating that "Technical data referring to power and torque was measured on an engine test stand at Ducati", their published values are 5% higher than the homologation values, in normal running order. Motorcycle weight is expressed in three ways: gross vehicle weight rating, dry weight and wet weight. GVWR is the maximum total weight of the motorcycle including all consumables, the rider, any passenger, any cargo.
It is well-understood and standardized, being defined by law and overseen by agencies such as the US Department of Transportation. In contrast and dry weight are unstandardized measurements that refer to the weight of the motorcycle without rider, passengers or cargo, either with or without a varying set of fluids such as fuel or lubricants, the battery. Wet and dry weight are used to make comparisons between different motorcycles, because all else being equal, a lighter motorcycle will perform and handle better than a heavier one; the difference between GVWR and wet weight is how much the motorcycle can safely carry, including the rider and other load. As its weight changes during riding, the dry weight of a motorcycle excludes the gasoline. Dry weight, in this sense, can directly be used for comparison with weight limits, which pertain to the motorcycle in operating condition, it is part of the homologation tests, it is found on the EC Certificate of Conformity as unladen mass. This dry weight could be useful in comparing different models, with different fuel tank capacities.
However, manufacturers may exclude some or all of the following: engine oil, coolant, or brake fluid, this makes such a comparison difficult. When any of these is exclu
Connecting rod
A connecting rod is a rigid member which connects a piston to a crank or crankshaft in a reciprocating engine. Together with the crank, it forms a simple mechanism that converts reciprocating motion into rotating motion. A connecting rod may convert rotating motion into reciprocating motion, its original use. Earlier mechanisms, such as the chain, could only impart pulling motion. Being rigid, a connecting rod may transmit either push or pull, allowing the rod to rotate the crank through both halves of a revolution. In a few two-stroke engines the connecting rod is only required to push. Today, the connecting rod is best known through its use in internal combustion piston engines, such as automobile engines; these are of a distinctly different design from earlier forms of connecting rod used in steam engines and steam locomotives. Evidence for the connecting rod appears in the late 3rd century Hierapolis sawmill in Roman Asia, it appears in two 6th century Byzantine-era saw mills excavated at Ephesus, Asia Minor and Gerasa, Roman Syria.
The crank and connecting rod mechanism of these Roman-era watermills converted the rotary motion of the waterwheel into the linear movement of the saw blades. Sometime between 1174 and 1206 in the Artuqid State, the Arab inventor and engineer Al-Jazari described a machine which incorporated the connecting rod with a crankshaft to pump water as part of a water-raising machine, though the device was complex. In Renaissance Italy, the earliest evidence of a − albeit mechanically misunderstood − compound crank and connecting-rod is found in the sketch books of Taccola. A sound understanding of the motion involved is displayed by the painter Pisanello who showed a piston-pump driven by a water-wheel and operated by two simple cranks and two connecting-rods. By the 16th century, evidence of cranks and connecting rods in the technological treatises and artwork of Renaissance Europe becomes abundant; the first steam engine, Newcomen's atmospheric engine, was single-acting: its piston only did work in one direction and so these used a chain rather than a connecting rod.
Their output rocked forth, rather than rotating continuously. Steam engines after this are double-acting: their internal pressure works on each side of the piston in turn; this requires a seal around the piston rod and so the hinge between the piston and connecting rod is placed outside the cylinder, in a large sliding bearing block called a crosshead. In a steam locomotive, the crank pins are mounted directly on one or more pairs of driving wheels, the axle of these wheels serves as the crankshaft; the connecting rods, run between the crank pins and crossheads, where they connect to the piston rods. Crossheads or trunk guides are used on large diesel engines manufactured for marine service; the connecting rods of smaller steam locomotives are of rectangular cross-section but, on small locomotives, marine-type rods of circular cross-section have been used. Stephen Lewin, who built both locomotive and marine engines, was a frequent user of round rods. Gresley's A4 Pacifics, such as Mallard, had an alloy steel connecting rod in the form of an I-beam with a web, only 0.375 in thick.
On Western Rivers steamboats, the connecting rods are properly called pitmans, are sometimes incorrectly referred to as pitman arms. In modern automotive internal combustion engines, the connecting rods are most made of steel for production engines, but can be made of T6-2024 and T651-7075 aluminum alloys or titanium for high-performance engines, or of cast iron for applications such as motor scooters, they are not rigidly fixed at either end, so that the angle between the connecting rod and the piston can change as the rod moves up and down and rotates around the crankshaft. Connecting rods in racing engines, may be called "billet" rods, if they are machined out of a solid billet of metal, rather than being cast or forged; the small end attaches to the piston pin, gudgeon pin or wrist pin, most press fit into the connecting rod but can swivel in the piston, a "floating wrist pin" design. The big end connects to the crankpin on the crank throw, in most engines running on replaceable bearing shells accessible via the connecting rod bolts which hold the bearing "cap" onto the big end.
There is a pinhole bored through the bearing on the big end of the connecting rod so that pressurized lubricating motor oil squirts out onto the thrust side of the cylinder wall to lubricate the travel of the pistons and piston rings. Most small two-stroke engines and some single cylinder four-stroke engines avoid the need for a pumped lubrication system by using a rolling-element bearing instead, however this requires the crankshaft to be pressed apart and back together in order to replace a connecting rod. A major source of engine wear is the sideways force exerted on the piston through the connecting rod by the crankshaft, which wears the cylinder into an oval cross-section rather than circular, making it impossible for piston rings to seal against the cylinder walls. Geometrically, it can be seen that longer connecting rods will reduce the amount of this sideways force, therefore lead to longer engine life
Multi-valve
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, delivering more power. A multi-valve engine design 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, 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, power output. 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 reduce wear on each cam lobe, allow more power from higher RPM without the danger of valve bounce; some engines are designed to open each intake valve at a different time, which increases turbulence, improving the mixing of air and fuel at low engine speeds.
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 headThis has two smaller intake valves. A three-valve layout allows better breathing than a two-valve head, but the large exhaust valve results in an RPM limit no higher than a two-valve head; the manufacturing cost for this design can be lower than for a four-valve design. The three-valve design was common in early 1990s; the Ducati ST3 V-twin had 3-valve heads. Four-valve cylinder headThis is the most common type of multi-valve head, with two exhaust valves and two similar inlet valves; this design allows similar breathing as compared to a three-valve head, as the small exhaust valves allow high RPM, this design is suitable for high power outputs.
Five-valve cylinder headLess common is the five-valve head, with two exhaust valves and three inlet valves. All five valves are similar in size; this design allows excellent breathing, and, as every valve is small, high RPM and high power outputs are theoretically available. Although, compared to a four-valve engine, a five-valve design should have a higher maximum RPM, the three inlet ports should give efficient cylinder-filling and high gas turbulence, it has been questioned whether a five-valve configuration gives a cost-effective benefit over four-valve designs. After making five-valve Genesis engines for several years, Yamaha has reverted to the cheaper four-valve design, examples of the five-valve engines is the various 1.8l 20vT engines manufactured by AUDI AG and the rare 1.6l 4A-GE engine of Toyota. Beyond five valvesFor 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 effective areas of differing valve quantities as proportion of cylinder bore.
These percentages are based on simple geometry and do not take into account orifices for spark plugs or injectors, but these voids will be sited in the "dead space" unavailable for valves. In practice, intake valves are larger than exhaust valves in heads with an number of valves-per-cylinder. 2 = 50% 3 = 64% 4 = 68% 5 = 68% 6 = 66% 7 = 64% 8 = 61% Turbocharging and supercharging are technologies that improve engine breathing, can be used instead of, or in conjunction with, multi-valve engines. 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 successful. Cylinder head porting, as part of engine tuning, is used to improve engine performance; the first motorcar in the world to have an engine with two overhead camshafts and four valves per cylinder was the 1912 Peugeot L76 Grand Prix race car designed by Ernest Henry. Its 7.6-litre monobloc straight-4 with modern hemispherical combustion chambers produced 148 bhp.
In April 1913, on the Brooklands racetrack in England, a specially built L76 called "la Torpille" beat the world speed record of 170 km/h. Robert Peugeot commissioned the young Ettore Bugatti to develop a GP racing car for the 1912 Grand Prix; this chain-driven Bugatti Type 18 had three valves per cylinder. It produced appr. 100 bhp at 2800 could reach 99 mph. The three-valve head would be used for some of Bugatti's most famous cars, including the 1922 Type 29 Grand Prix racer and the legendary Type 35 of 1924. Both Type 29 and Type 35 had a 100 bhp 2-liter SOHC 24-valve NA straight-8 that produced 0.82 bhp per cubic inch. A. L. F. A. 40/60 GP was a working early racing car prototype made by the company now called Alfa Romeo. Only one example was built in 1914, modified in 1921; this design of Giuseppe Merosi was the first Alfa Romeo DOHC engine. It had four valves per 90-degree valve angle and twin-spark ignition; the GP engine had a displacement of 4.5-liter and produced 88 bhp at 2950 rpm, after modifi
Joey Dunlop
William Joseph Dunlop, was a Northern Irish motorcyclist from Ballymoney. In 2016 he was voted through Motorcycle News as the 5th greatest motorcycling icon behind Valentino Rossi, his achievements include three hat-tricks at the Isle of Man TT meeting, where he won a record 26 races in total. Dunlop's name is amongst the most revered by fans of motorcycle racing; this iconic stature, coupled to Dunlop's somewhat shy and unassuming persona, has led to him being seen as a true working class hero. Such attributes endeared him to fans of motorcycling across the world. During his career he won the Ulster Grand Prix 24 times. In 1986, he won a fifth consecutive TT Formula One world title, he was awarded the MBE in 1986 for his services to the sport, in 1996 he was awarded the OBE for his humanitarian work for children in Romanian orphanages, to which he had delivered clothing and food. Joey - The Man Who Conquered the TT, a documentary focussed on Dunlop's racing career, was released in 2013. Another documentary, based on the life of Dunlop and his brothers, was released in the UK and Ireland on 11 June 2014.
Dunlop helped orphans in Balkans, driving a van loaded with supplies to orphanages in Romania and Bosnia-Hercegovina before the annual racing season began. In 1996, he received an OBE for his humanitarian work. After Dunlop's death, the Joey Dunlop Foundation was initiated, a charity that provides appropriate accommodation for disabled visitors to the Isle of Man. On 30 January 2015, Dunlop was voted Northern Ireland's greatest sports star by readers of the Belfast Telegraph newspaper. On the night of 23 May 1985, Dunlop was travelling from Northern Ireland to the Isle of Man for the annual TT races by sea, aboard the Tornamona, a former fishing boat; the vessel had departed from Strangford, County Down with Dunlop, other riders and equipment aboard. Strong currents into Strangford Lough pushed the Tornamona onto St Patrick’s Rock where her rudder broke off in a crevice; the boat sank and all 13 passengers and crew were rescued by the Portaferry Lifeboat. The bikes were recovered by divers. Dunlop died in Tallinn, Estonia, in 2000 while leading a 125cc race on Pirita-Kose-Kloostrimetsa Circuit.
He appeared to lose control of his bike in the wet conditions and was killed on impact with trees. As a mark of respect, the Estonian government's official website was replaced with a tribute to Dunlop within hours of his death. Northern Ireland television carried live coverage of his funeral. Fifty thousand mourners, including bikers from all parts of Britain and Ireland and people from all backgrounds in Northern Ireland, attended the funeral procession to Garryduff Presbyterian church and his burial in the adjoining graveyard; the most successful overall rider at the annual TT races is awarded the "Joey Dunlop Cup". A memorial statue was erected in his home town of Ballymoney. On the Isle of Man, a statue of Dunlop astride a Honda overlooks the Bungalow Bend at Snaefell and the 26th Milestone area of the TT course was named "Joey's". Irish publishers The O'Brien Press produced a full-colour pictorial tribute to Dunlop following his death. Northern Ireland band Therapy? recorded a song in memory of Dunlop, called Joey.
Dunlop was anti-sectarian. Both Catholics and Protestants supported him. Superstitious, he always wore a red T-shirt and a yellow crash helmet. Robert Dunlop, Joey Dunlop's younger brother who died after a practice crash at the 2008 North West 200. William Dunlop, Joey Dunlop's nephew and Robert's son, who died after a practice crash at the 2018 Skerries 100. Michael Dunlop, Joey Dunlop's nephew, Robert's son and William's brother. List of people on stamps of Ireland The official Joey Dunlop website Joey Dunlop Foundation Tribute page on the TT website University of Ulster news release Billd's Joey stamps on Flickr North West 200 Official Website MFV Tornamona at Irish Wrecks Online
Bicycle and motorcycle geometry
Bicycle and motorcycle geometry is the collection of key measurements that define a particular bike configuration. Primary among these are wheelbase, steering axis angle, fork offset, trail; these parameters have a major influence on. Wheelbase is the horizontal distance between the centers of rear wheels. Wheelbase is a function of rear frame length, steering axis angle, fork offset, it is similar to the term wheelbase used for trains. Wheelbase has a major influence on the longitudinal stability of a bike, along with the height of the center of mass of the combined bike and rider. Short bikes are much more suitable for performing stoppies; the steering axis angle called caster angle or head angle, is the angle that the steering axis makes with the horizontal or vertical, depending on convention. The steering axis is the axis; the steering axis angle matches the angle of the head tube. In bicycles, the steering axis angle is measured from the horizontal. For example, Lemond offers: a 2007 Filmore, designed for the track, with a head angle that varies from 72.5° to 74° depending on frame size a 2006 Tete de Course, designed for road racing, with a head angle that varies from 71.25° to 74°, depending on frame size.
Due to front fork suspension, modern mountain bikes - as opposed to road bikes - tend to have slacker head tube angles around 70° although they can be as low as 62°. At least one manufacturer, Cane Creek, offers an after-market threadless headset that enables changing the head angle. In motorcycles, the steering axis angle is called the rake angle or just rake and is measured from the vertical. For example, Moto Guzzi offers: a 2007 Breva V 1100 with a rake of 25°30’ a 2007 Nevada Classic 750 with a rake of 27.5° The fork offset is the perpendicular distance from the steering axis to the center of the front wheel. In bicycles, fork offset is called fork rake. Road racing bicycle forks have an offset of 40–50 mm; the offset may be implemented by curving the forks, adding a perpendicular tab at their lower ends, offseting the fork blade sockets of the fork crown ahead of the steerer, or by mounting the forks into the crown at an angle to the steer tube. The development of forks with curves is attributed to George Singer.
In motorcycles with telescopic fork tubes, fork offset can be implemented by either an offset in the triple tree, adding a triple tree rake to the fork tubes as they mount into the triple tree, or a combination of the two. Other, less-common motorcycle forks, such as trailing link or leading link forks, can implement offset by the length of link arms; the length of a fork is measured parallel to the steer tube from the lower fork crown bearing to the axle center. Trail, or caster, is the horizontal distance from where the front wheel touches the ground to where the steering axis intersects the ground; the measurement is considered positive if the front wheel ground contact point is behind the steering axis intersection with the ground. Most bikes have positive trail, though a few, such as the two-mass-skate bicycle and the Python Lowracer have negative trail. Trail is cited as an important determinant of bicycle handling characteristics, is sometimes listed in bicycle manufacturers' geometry data, although Wilson and Papodopoulos argue that mechanical trail may be a more important and informative variable, although they both describe nearly the same thing.
Trail is a function of steering axis angle, fork offset, wheel size. Their relationship can be described by this formula: Trail bicycle = R w cos − O f sin and Trail motorcycle = R w sin − O f cos where R w is wheel radius, A h is the bicycle head angle measured from the horizontal, A r is the motorcycle rake angle measured from the vertical, O f is the fork offset. Trail can be increased by increasing the wheel size, decreasing or slackening the head angle, or decreasing the fork offset. Trail decreases as head angle increases, as wheel diameter decreases. Motorcyclists tend to speak of trail in relation to rake angle; the larger the rake angle the larger the trail. Note that, on a bicycle, as rake angle increases, head angle decreases. Trail can vary as the bike steers. In the case of traditional geometry, trail decreases as the bike leans and steers in the direction of
Honda RVF750 RC45
The Honda RVF750R RC45 was a faired racing motorcycle created for homologation purposes for the Superbike World Championship by Honda Racing Corporation. The RVF750R was the successor to the VFR750R RC30. Like its predecessor, the RVF750R featured a DOHC liquid cooled V4 4-stroke engine and a single-sided swingarm with gear driven cams, but unlike the RC30 it utilized electronic fuel injection, in a setup similar to the production 1992 NR750; the US spec engine was rated at 101 horsepower. A simple rewire modification to the PGM-FI box increased power in the US engine up to the 118 hp, it was manufactured from 1994 until 1995 and sold in limited numbers, followed by the VTR1000R SP-1 RC51 in 2000. Unlike the VFR750R RC30 and VFR750F from which the engine was derived the gear drive for the cams was moved from the centre of the engine in between the cylinders to the one side allowing a narrower engine; the RC45 has its roots from the original 1982 Honda V-45 V-four 750 engines introduced on the 1982 Honda Magna and Sabre models.
In 1986, the 2nd generation V-four arrived in the form of the VFR750F, fixing the camshaft problem that plagued the original V-four and moving to gear driven cams. In 1988, the RC30 was born, loosely based on the RVF endurance racer, this was used to contest the newly formed Superbike World Championship. Only 300 were imported into the US for only one year, 1990. In 1994, with the RC30 showing its age and being handily beaten by the Ducatis, Honda redesigned the RC30 using more of the technology from the RVF endurance racer and released the RC45 to much fanfare. Only 200 were manufactured worldwide and per AMA homologation rules 50 were imported into the US, with 20 of them going to private race teams, it is one of the rarest motorcycles produced by Honda. In its peak race form, in 1999, the RC45 made over 190 hp, with some calling it the best Superbike machine ever. In its career HRC modified the bike to keep it competitive including new exhaust systems and switching back to a standard two-sided swingarm for increased strength on non-endurance bikes.
The RC51 was released in 2000 to make use of the 250cc displacement advantage for V-twin motorcycles that allowed the Ducatis to be so competitive. The RC45 was shadowed with problems; this did not bode well with Honda, who entered the World Superbike championship with full factory support, not just privateer support that they gave to teams with the RC30. Castrol was the major sponsor of the RC45, Honda came to win; the RC45 only won one World Superbike championship with American John Kocinski when he won the 1997 FIM Superbike World Championship. Jim Moodie from a standing start, on an RC45 Honda lapped in 18:11.4 seconds, 124.45 mph in the 1999 Isle of Man TT. Miguel Duhamel won the 1995 US AMA Superbike and the 1996 Daytona 200 on an RC45. Miguel came in 2nd in 1996 and 2nd again 1997 on the RC45 a season ending crash in 1998 injured his leg. However, Ben Bostrom won the 1998 AMA Superbike Championship on an RC45; the bike was used to win the Endurance FIM World Championship six times between 1984 and 1998.
Michael Rutter won the 1998 Macau Grand Prix. The RVF400R resembles the RVF750R with the exception of the headlights, which are large and round on the 750. If there was a bike that had a reputation to live up to it was Honda’s RC45. Part of the success story of the RC30 was that it was a hand-built race bike, available at a cost that many club racers could afford, so though the number of victories in World Super Bike were only a few, The bike excelled at a level where up until now only expensive works bikes could have any chance of competing towards the front end of a race field. With the RC45, Honda drew on its extensive knowledge of racing the factory RVF racers. Many engineering ideas were brought across to the RC45. Honda wanted to produce another no-expenses-spared race machine. Just a short time earlier the complex NR750 had been released for road use, a bike which to this day is still considered an engineering masterpiece; some of the technology of the NR750 was carried across to the RC45, These included its fuel-injection system, sprag clutch and the 16-inch front wheel size.
Some of the RC45's specifications: V4 close firing order motor Lightweight low friction pistons Titanium conrods Ceramic and graphite impregnated cylinder liners Close ratio gearbox with undercut shift dogs Separate air cooled oil heat exchanger Many of the engine components were cast from magnesium to save weight Cast upper and forged lower triple clamps SHOWA front and rear suspension 6.00 inch rear rim carrying a 190/50/17 tire Major development changes were made to the RC45’s engine, one of the first differences seen is the bore and stroke, which are much different from the RC30. The RC45 had a reduced stroke compared to the RC30, the RC30 having used a bore and stroke of 70 mm x 48.6 mm, whereas the RC45 was changed to a more over-square stroke ratio of 72 mm bore and 46 mm stroke. This allowed higher maximum engine revolutions than the RC30. Where the RC30 had used roller bearings on the camshafts, the RC45 used more conventional plain bearings; the RC30 had used a piston with oil control ring to reduce friction.
This was effective for racing but resulted in increased oil consu
Compression ratio
The static compression ratio, of an internal combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity. It is a fundamental specification for many common combustion engines. In a piston engine, it is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, the volume of the combustion chamber when the piston is at the top of its stroke. For example, a cylinder and its combustion chamber with the piston at the bottom of its stroke may contain 1000 cc of air; when the piston has moved up to the top of its stroke inside the cylinder, the remaining volume inside the head or combustion chamber has been reduced to 100 cc the compression ratio would be proportionally described as 1000:100, or with fractional reduction, a 10:1 compression ratio. A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air–fuel mixture due to its higher thermal efficiency.
This occurs because internal combustion engines are heat engines, higher efficiency is created because higher compression ratios permit the same combustion temperature to be reached with less fuel, while giving a longer expansion cycle, creating more mechanical power output and lowering the exhaust temperature. It may be more helpful to think of it as an "expansion ratio", since more expansion reduces the temperature of the exhaust gases, therefore the energy wasted to the atmosphere. Diesel engines have a higher peak combustion temperature than petrol engines, but the greater expansion means they reject less heat in their cooler exhaust. Higher compression ratios will however make gasoline engines subject to engine knocking if lower octane-rated fuel is used; this can reduce efficiency or damage the engine if knock sensors are not present to modify the ignition timing. On the other hand, diesel engines operate on the principle of compression ignition, so that a fuel which resists autoignition will cause late ignition, which will lead to engine knock.
Static compression ratio is calculated by the formula C R = V d + V c V c Where: V d = displacement volume. This is the volume inside the cylinder displaced by the piston from the beginning of the compression stroke to the end of the stroke. V c = clearance volume; this is the volume of the space in the cylinder left at the end of the compression stroke. V d can be estimated by the cylinder volume formula V d = π 4 b 2 s Where: b = cylinder bore s = piston stroke lengthBecause of the complex shape of V c it is measured directly; this is done by filling the cylinder with liquid and measuring the volume of the used liquid. The compression ratio in a gasoline -powered engine will not be much higher than 10:1 due to potential engine knocking and not lower than 6:1; some production automotive engines built for high performance from 1955–1972, used high-octane leaded gasoline or'5 star' to allow compression ratios as high as 13.0:1. A technique used to prevent the onset of knock is the high "swirl" engine that forces the intake charge to adopt a fast circular rotation in the cylinder during compression that provides quicker and more complete combustion.
It is possible to manufacture gasoline engines with compression ratios of over 11:1 that can use 87 /2 fuel with the addition of variable valve timing and knock sensors to delay ignition timing. Such engines may not produce their full rated power using 87 octane gasoline under all circumstances, due to the delayed ignition timing. Direct fuel injection, which can inject fuel only at the time of fuel ignition, is another recent development which allows for higher compression ratios on gasoline engines; the compression ratio can be as high as 14:1 in engines with a'ping' or'knock' sensor and an electronic control unit. In 1981, Jaguar released a cylinder head; the cylinder head design was known as the "May Fireball" head. In 2012, Mazda released new petrol engines under the brand name SkyActiv with a 14:1 compression ratio, to be used in all Mazda vehicles by 2015; the SkyActiv engine achieves this compression ratio with ordinary unleaded gasoline through improved scavenging of exhaust gases, in addition to direct injection.
In a turbocharged or supercharged gasoline engine, the CR is customarily built at 10.5:1 or lower. This is due to the turbocharger/supercharger having compressed the air before it enters the cylinders. Port fuel injected engines run lower boost than direct fuel injected engines because port fuel inj
