Explanation-and-history-of-horsepower General Reference Explanation-and-history-of-horsepower The term 'horse power' is largely credited to James Watt, in the late 1700s. Watt was a Scottish engineer who invented a number of improvements to steam engines, which he then (in partnership) began to manufacture and sell (the first units going into service in 1776). Most of Watt's potential clients were using horses, so he soon found that in order to market his engines, he needed to express the power of his engines in terms of how many horses a given engine would replace. For this purpose, he first calculated the average power of a horse, which he termed 'horsepower'. He then specified for each of his engines how much 'horsepower' it had (i.e. of how many horses it had the equivalent power of). Due to the success of his steam engine business, the term 'horsepower' came to be recognized. His competitors and other machine manufacturers copied his approach, also expressing the power of their engines in 'horsepower', which resulted in it becoming a standard measure of power.

To calculate the force of a horse, Watt first observed that a common use of horses was to walk in a circle, pushing a beam attached to a mill wheel (see following illustration). He then noted that the circle that the horse would walk was typically about 12 feet in radius, so the distance around the circle (circumference) would be about 75 feet (2.4 × 2π × 12). He also measured that a horse would go around the circle an average of 144 times per hour and he judged that as the horse walked it pulled with a force of about 180 pounds. Multiplying this out and then rounding off, he ended up with a figure of 33,000 foot-pounds per minute. Although Watt was the first to widely publicize a measure of horse power, he was not the first to come up with the idea. In 1702 (almost a century earlier), Thomas Savery wrote in The Miner's Friend about the idea of expressing the power of engines in terms of horse equivalents. However, it was Watt who first took the idea and introduced it into widespread use.

Other people have measured the power of horses and ended up with somewhat different figures; John Smeaton estimated it at 22,916 foot-pounds/minute and John Desaguliers produced a figure of 27,500 foot-pounds/minute. However, the figure produced by Watt was accepted as the standard definition of horsepower. Alternative Histories Some historians have disputed the details of how Watt calculated the power of a horse. For example, some say that he actually calculated the power of a pit pony (a type of pony commonly used in UK mining) and then added 50% to determine the power of a horse. Consequently, the exact method which Watt used to calculate the value of a 'horse power' is open to dispute, but the remaining historical details are well documented and accepted. Horse Equivalents The actual power which a horse can exert depends largely on the duration over which the horse must work. Watt's calculation was based on a 4-hour working shift, where the horse would then rest before working again. If a horse works for very short periods, it can exert higher levels of force.

For example, a horse can exert the equivalent of up to 15 horsepower, if the effort is just a few seconds. Alternatively, if a horse has long working shifts, the amount of force it exerts over this longer period will be less. On the other hand, a machine works continuously, producing the same level of power at all times. So, a 1-horsepower machine working 24 hours a day will do 3 times as much work as a horse working two 4-hour shifts. Consequently, taking into account the working hours of a horse per day, a machine which is in continuous use would be equal to about three times as many horses as its specified horsepower would indicate. For example, in this case a machine of 2 horsepower would in fact replace about 6 horses (each of which work an average of 8 hours per day). Note also that the term horsepower is an approximate calculation for a working horse. Depending on various factors (race, health, size, condition, age, application), the actual power and working capability of the individual horse could be higher or lower than 1 horsepower.

horsepower | unit of measurement | Britannica.com unit of measurement power Horsepower, the common unit of power; i.e., the rate at which work is done. In the British Imperial System , one horsepower equals 33,000 foot-pounds of work per minute—that is, the power necessary to lift a total mass of 33,000 pounds one foot in one minute . This value was adopted by the Scottish engineer James Watt in the late 18th century, after experiments with strong dray horses, and is actually about 50 percent more than the rate that an average horse can sustain for a working day . The electrical equivalent of one horsepower is 746 watts in the International System of Units (SI), and the heat equivalent is 2,545 BTU ( British Thermal Units ) per hour . Another unit of power is the metric horsepower, which equals 4,500 kilogram-metres per minute (32,549 foot-pounds per minute), or 0.9863 horsepower.

Horsepower at the output shaft of an engine, turbine , or motor is termed brake horsepower or shaft horsepower, depending on what kind of instrument is used to measure it. Horsepower of reciprocating engines , particularly in the larger sizes, is often expressed as indicated horsepower , which is determined from the pressure in the cylinders. Brake or shaft horsepower is less than indicated horsepower by the amount of power lost to friction within the engine itself, which may amount to 10 percent or more of the indicated horsepower. Electric motor horsepower can be determined from the electrical input in watts, allowing for heat and friction losses in the motor itself. Thrust horsepower of jet engines and rockets is equal to the thrust in pounds force times the speed of the vehicle in miles per hour divided by 375 (which is equal to one horsepower measured in mile-pounds per hour). Learn More in these related articles: How Horsepower Works | HowStuffWorks How Horsepower Works Alexandra Wyman/WireImage Two high-horsepower Dodge Challengers line up at the drag strip. See more sports car pictures . Chances are you've heard about horsepower.

Just about every car ad on TV mentions it, people talking about their cars bandy the word about and even most lawn mowers have a big sticker on them to tell you the horsepower rating. But what is horsepower, and what does the horsepower rating mean in terms of performance? In this article, you'll learn exactly what horsepower is and how you can apply it to your everyday life. The term horsepower was invented by the engineer James Watt. Watt lived from 1736 to 1819 and is most famous for his work on improving the performance of steam engines . We are also reminded of him every day when we talk about 60-watt light bulbs . Next Up TreeHugger.com: Top 5 Engine Technologies The story goes that Watt was working with ponies lifting coal at a coal mine, and he wanted a way to talk about the power available from one of these animals. He found that, on average, a mine pony could do 22,000 foot-pounds of work in a minute. He then increased that number by 50 percent and pegged the measurement of horsepower at 33,000 foot-pounds of work in one minute.

It is that arbitrary unit of measure that has made its way down through the centuries and now appears on your car, your lawn mower, your chain saw and even in some cases your vacuum cleaner . What horsepower means is this: In Watt's judgement, one horse can do 33,000 foot-pounds of work every minute. So, imagine a horse raising coal out of a coal mine as shown above. A horse exerting 1 horsepower can raise 330 pounds of coal 100 feet in a minute, or 33 pounds of coal 1,000 feet in one minute, or 1,000 pounds 33 feet in one minute. You can make up whatever combination of feet and pounds you like. As long as the product is 33,000 foot-pounds in one minute, you have a horsepower. ­Y­ou can probably imagine that you would not want to load 33,000 pounds of coal in the bucket and ask the horse to move it 1 foot in a minute because the horse couldn't budge that big a load.

You can probably also imagine that you would not want to put 1 pound of coal in the bucket and ask the horse to run 33,000 feet in one minute, since that translates into 375 miles per hour and horses can't run that fast. However, if you have read How a Block and Tackle Works , you know that with a block and tackle you can easily trade perceived weight for distance using an arrangement of pulleys. So you could create a block and tackle system that puts a comfortable amount of weight on the horse at a comfortable speed no matter how much weight is actually in the bucket. Horsepower can be converted into other units as well. For example: 1 horsepower is equivalent to 746 watts. So if you took a 1-horsepower horse and put it on a treadmill, it could operate a generator producing a continuous 746 watts. 1 horsepower (over the course of an hour) is equivalent to 2,545 BTU (British thermal units).

If you took that 746 watts and ran it through an electric heater for an hour, it would produce 2,545 BTU (where a BTU is the amount of energy needed to raise the temperature of 1 pound of water 1 degree F). One BTU is equal to 1,055 joules, or 252 gram-calories or 0.252 food Calories . Presumably, a horse producing 1 horsepower would burn 641 Calories in one hour if it were 100-percent efficient. In this article, you'll learn all about horsepower and what it means in reference to machines. Horsepower - Example Problems Horsepower Jump to: navigation , search This article is about the unit of measurement. For the machine which used horses to generate power, see horse power (machine) . The horsepower (hp) is the name of several non-metric units of power . In scientific discourse the term "horsepower" is rarely used due to the various definitions and the existence of an SI unit for power, the watt (W).

However, the idea of horsepower persists as a legacy term in many languages, particularly in the automotive industry for listing the maximum power of internal-combustion engines . The various types of horsepower (metric) are: Contents According to the most common definition of horsepower, one horsepower is defined as exactly: 1 hp = 745.69987158227022 W A common memory aid is based on the fact that Christopher Columbus first sailed to the Americas in 1492 . The memory aid states that 1 hp = 1/2 Columbus or 746 W. In fourteen hundred and ninety-two Columbus sailed the ocean blue. Divide that son-of-a-gun by two And that's how many watts there are in a horsepower. The horsepower was first used by James Watt during a business venture where his steam engines replaced horses . It was defined that a horse can lift 33,000 pounds force with a speed of 1 foot per minute : 33,000 ft · lbf · min −1. This is sometimes called a mechanical horsepower to distinguish it from the other definitions of horsepower below.

Engine horsepower The power of an engine may be measured or estimated at several points in the transmission of the power from its generation to its application. A number of names are used for the power developed at various stages in this process: Indicated horsepower (ihp) Indicated horsepower is the theoretical power of a reciprocating engine assuming that it is completely efficient in converting the energy contained in the expanding gases in the cylinders. It is calculated from the pressures developed in the cylinders, measured by a device called an engine indicator - hence indicated horsepower. It was the figure normally used for steam engines in the 19th century but is misleading because the mechanical efficiency of an engine means that the actual power output may be only 70% to 90% of the indicated horsepower. Brake horsepower (bhp) Brake horsepower was a term commonly used before the 1970s in the United States , and is still common in the United Kingdom . It refers to the brake dynamometer , the device for measuring the true power of the engine. Stating power in 'bhp' gives some indication that this is a true reading, rather than a calculated or predicted one.

However, it does not tell where the power reading was taken — at the flywheel, transmission or drive wheels. hp (SAE) In the United States the term "bhp" fell into disuse after the American Society of Automotive Engineers (SAE) recommended manufacturers use "hp (SAE)" to indicate the power of the engine, given that particular car's complete engine installation. It measures engine power at the flywheel , not counting drivetrain losses. Prior to 1972 most American automakers rated their engines in terms of SAE gross horsepower (defined under SAE standards J245 and J1995). Gross hp was measured using a blueprinted test engine running on a stand without accessories, mufflers, or emissions control devices. It therefore reflected a maximum, theoretical value, not the power of an installed engine in a street car. Gross horsepower figures were also subject to considerable adjustment by carmakers: the power ratings of mass-market engines were often exaggerated, while those for the highest-performance muscle car engines were frequently underrated. Starting in 1971 automakers began to quote power in terms of SAE net horsepower (as defined by standard J1349).

This reflected the rated power of the engine in as-installed trim, with all accessories and standard intake and exhaust systems. By 1972 U.S. carmakers quoted power exclusively in SAE net hp. The change was meant to 'deflate' power ratings to assuage the auto insurance industry and environmental and safety lobbies, as well as to obfuscate the power losses caused by emissions -control equipment. SAE net ratings, while more accurate than gross ratings, still represent the engine's power at the flywheel. Contrary to some reports, it does not measure power at the drive wheels. Because SAE gross ratings were applied liberally, at best, there is no precise conversion from gross to net. Comparison of gross and net ratings for unchanged engines show a variance of anywhere from 40 to 150 horsepower. The Chrysler 426 Hemi , for example, in 1971 carried a 425 hp gross rating (often considered to be underrated) and a net rating of 375 hp. hp (DIN) This is the power measured according to the German standard DIN 70020.

It is measured at the flywheel, and is in practical terms equivalent to the SAE net figure. However, be aware that DIN "horsepower" may in fact be expressed in PS (Pferdestärke) - see "Metric horsepower" below. SAE-certified horsepower In 2005 , the Society of Automotive Engineers introduced a new test procedure ( J2723 ) for engine horsepower and torque . The procedure eliminates some of the areas of flexibility in power measurement, and requires an independent observer present when engines are measured. The test is voluntary, but engines completing it can be advertised as "SAE-certified". Many manufacturers began switching to the new rating immediately, often with surprising results. The rated output of Cadillac 's Northstar V8 jumped from 440 hp (328 kW) to 469 hp (350 kW) under the new tests, while the rating for Toyota 's Camry 3.0 L 1MZ-FE V6 fell from 210 hp (157 kW) to 190 hp (142 kW).

The first engine certified under the new program was the 7.0 L LS7 used in the 2006 Chevrolet Corvette Z06. Certified power rose slightly from 500 hp (373 kW) to 505 hp (377 kW). Drawbar horsepower (dbhp) Drawbar horsepower is the power a railroad locomotive has available to haul a train or an agricultural tractor to pull an implement. This is a measured figure rather than a calculated one. A special railroad car called a dynamometer car coupled behind the locomotive keeps a continuous record of the drawbar pull exerted, and the speed. From these, the power generated can be calculated. To determine the maximum power available, a controllable load is required; this is normally a second locomotive with its brakes applied, in addition to a static load. Shaft horsepower (shp) Shaft horsepower is the power delivered to the propellor shaft of a ship or turboprop airplane. This may be measured, or estimated from the indicated horsepower given a standard figure for the losses in the transmission (typical figures are around 10%). Effective horsepower (ehp) Effective horsepower is the power converted to useful work.

In the case of a vehicle this is the power actually turned into forward motion. Summary for a ship Indicated horsepower (theoretical capability of the engine) minus frictional losses within the engine (bearings, rods, etc), equals Brake horsepower (power delivered directly by the engine) minus frictional losses in the transmission (bearings, gears, etc.), equals Shaft horsepower (power delivered to the shaft) minus shaft losses (slip, cavitation , etc), equals Effective horsepower RAC horsepower (taxable horsepower) This measure was instituted by the Royal Automobile Club in Britain and used to denote the power of early 20th century British cars . Many cars took their names from this figure (hence the Austin Seven and Riley Nine), while others had names such as "40/50hp", which indicated the RAC figure followed by the true measured power. Taxable horsepower does not reflect developed horsepower; rather, it is a calculated figure based on the engine's bore size, number of cylinders, and a (now archaic) presumption of engine efficiency. As new engines were designed with ever-increasing efficiency, it was no longer a useful measure, but was kept in use by UK regulations which used the rating for tax purposes .

where D is the diameter (or bore) of the cylinder in inches n is the number of cylinders This is equal to the displacement in cubic inches divided by 10π then divided again by the stroke in inches. [1] Since taxable horsepower was computed based on bore and number of cylinders, not based on actual displacement, it gave rise to engines with 'undersquare' dimensions, i.e., relatively narrow bore, but long stroke; this tended to impose an artificially low limit on rotational speed ( rpm ), hampering the true power output and efficiency of the engine. The situation persisted for several generations of four- and six-cylinder British engines: for example, Jaguar's 3.8-litre XK engine had six cylinders with a bore of 87 mm (3.43 in) and a stroke of 106 mm (4.17 in), where most American automakers had long since moved to oversquare (wide bore, short stroke) V-8s. Metric horsepower PS This unit (German: Pferdestärke = horse strength) is no longer a lawful unit, but is still commonly used in Europe, South America and Japan, especially by the automotive and motorcycle industry.

It was adopted throughout continental Europe with designations equivalent to the English "horse power", but mathematically different from the British unit. It is defined by the Physikalisch-Technische Bundesanstalt (PTB) [2] in Braunschweig as exactly: 1 PS = 75 kp ·m/s = 735.49875 W = 0.9863201652997627 hp (SAE) The PS was adopted by the Deutsches Institut für Normung (DIN) , and subsequently, by the automotive industry throughout most of Europe. (In the nineteenth century, however, the French did not use this German unit, but had one of their own, the Poncelet .) In 1992, the PS was rendered obsolete by EEC directives, where it was replaced by the kilo watt as the official power measuring unit, but in situations where horsepower was used for commercial and advertising purposes, it continued to be used, as customers are not familiar with the usage of kilowatts for combustion engines.

The European and Japanese automotive industries may use "horsepower" or "hp" (rather than "PS" or "CV", etc.) when referring to metric horsepower in their press-releases or in the media. pk A Dutch paardekracht equals the German Pferdestärke hence 1 pk = 735.49875 W CV Often the French name for the Pferdestärke. Also a French unit for tax horsepower , short for chevaux vapeur ("steam horses") or cheval-vapeur, hence Citroën 2CV . In Italy, Spain, Portugal and Brazil, 'CV' is the equivalent to the German 'PS'. ch This is a French unit for automobile power. The symbol ch is short for chevaux ("horses"). Some sources give it as 735.5 W, but it is generally used interchangeably with the German 'PS'. Boiler horsepower A boiler horsepower is used for boilers in power plants . It is equal to 33,475 Btu /h (9.8095 kW). Electrical horsepower The electrical horsepower is used by the electrical industry for electric motors and is defined to be exactly 746 watts.

History of the term "horsepower" The term "horsepower" was invented by James Watt to help market his improved steam engine . He had previously agreed to take royalties of one third of the savings in coal from the older Newcomen steam engines [3] . This royalty scheme did not work with customers who did not have existing steam engines but used horses instead. Watt determined that a horse could turn a mill wheel 144 times in an hour (or 2.4 times a minute). The wheel was 12 feet in radius, thus in a minute the horse travelled 2.4 × 2π × 12 feet. Watt judged that the horse could pull with a force of 180 pounds (just assuming that the measurements of mass were equivalent to measurements of force in pounds-force, which were not well-defined units at the time). So: This was rounded to an even 33,000 ft·lbf/min [4] . Others recount that Watt determined that a pony could lift an average 220 pounds 100 feet (30 m) per minute over a four-hour working shift.

Watt then judged a horse was 50% more powerful than a pony and thus arrived at the 33,000 ft·lbf/min figure [5] . Engineering in History recounts that John Smeaton initially estimated that a horse could produce 22,916 foot-pounds per minute. John Desaguliers increased that to 27,500 foot-pounds per minute. "Watt found by experiment in 1782 that a 'brewery horse' was able to produce 32,400 foot-pounds per minute". James Watt and Matthew Boulton standardized that figure at 33,000 the next year [6] . Put into perspective, a healthy human can sustain about 0.1 horsepower. Most observers familiar with horses and their capabilities estimate that Watt was either a bit optimistic or intended to underpromise and overdeliver; few horses can maintain that effort for long. Regardless, comparison to a horse proved to be an enduring marketing tool.

Conversion of historical definition to watts The historical value of 33,000 ft·lbf/min may be converted to the SI unit of watts by using the following conversion of units factors: 1 ft = 0.3048 m 1 lbf = g n × 1 lb = 9.80665 m/s2 × 1 lb × 0.45359237 kg/lb = 4.44822 kg·m/s2 = 4.44822 N 60 seconds = 1 minute And the watt is defined as so the historical figure of 33,000 ft·lbf/min converts exactly to the modern definition. References H.W.Dickenson, James Watt - Craftsman and Engineer, Cambridge University Press, 1936, p 145.

Richard Shelton Kirby, et al, Engineering in History, Courier Dover Publications, 1990, p 171, ISBN 0486264122 External links Horsepower-types General Reference Horsepower-types The concept of ' horse power ' was originally developed for machines (initially for steam engines) and was estimated at 33,000 foot-pounds per minute, which is exactly 550 foot-pounds per second. However, with the development of other types of engines (e.g. electrical engines), slightly different figures were used. This has resulted in varioius different 'horse power' measures, as follows: HP Measure 735.49875 Some notes on the above: In addition to defining the measure horsepower, due to his many contributions to practical science, the term 'watt' was named after the scientist and inventor James Watt. With the development of electrical motors, their input is in terms of electrical watts so it is reasonable to define their output in terms of watts. For simplicity, the watt equivalent of mechanical HP was rounded off to 746 watts.

As the Imperial/British/USA system uses measures (foot, pound) which are not available in the metric system, users of the metric system created a measure (metric HP) which uses metric measures (kilogram, meter) and is approximately the same value. In Europe and some other countries, the term PS is often used instead of metric HP, as the Germans were the first to widely use metric HP and consequently popularized the German term (In German, Pferde = horse and Stärke=power). Equivalent abbreviations in other languages include pk (Dutch), ch (French), hk (Finnish), hv (Norwegian/Danish), LE (Hungarian), k/ks (Czech and Slovak), KS (Croatian and Servian), KM (Slovenian), CP (Romanian), KC (Macedonian). There are a number of other variations of HP, which are not in common use. These include: Boiler HP. For steam engines and steam turbines, the term boiler HP was created. It is related to the amount of water which can be evaporated per unit time.

However, as the efficiency of steam engines varies, the actual power output is not closely related to the amount of steam produced, so this measure has largely fallen out of use. Drawbar HP. This is typically used as a measure of the drawing power of railway locomotives and agricultural tractors. Point of Measurement The power of an engine can be measured at various points. For example, with a car, one could measure HP at the engine or at the drive shaft or at the wheels. The highest figure would be at the engine itself, somewhat lower at the drive shaft and lowest of all at the wheels (due to frictional and mechanical losses associated with intermediate mechanical components). Consequently, a car manufacturer measuring HP at the engine output will get higher figures than a car manufacturer measuring HP at the wheels. To prevent such discrepancies, the term 'horse power' can be preceded by a qualifier to indicate where it is measured. These include: Crankshaft or Brake or Net. Crankshaft horsepower is the power delivered to the crankshaft and measured at this point.

It is commonly referred to at brake horsepower (named after the device called a 'brake', which is used to measure the torque and rotational speed of the crankshaft and thus calculate the HP) and is often abbreviated to BHP (see below section 'BHP abbreviation'). As the measurement is made at the crankshaft, it measures power before losses to elements such as the gearbox, differential, alternator, muffler, cooling system and so on. Shaft. Shaft horsepower is the power measured at the output shaft of the transmission. It is commonly used for ships and airplanes but seldom for cars. Effective or True. Effective horsepower or true horsepower (abbreviated to THP) is the actual power at the wheels. It is less than the brake or shaft horsepower, as it is measured after the various mechanical losses between the engine and the wheels. However, it is a more meaningful measure of the power available for the primary function of the car, given rise to the qualifier 'true'. This measurement is also referred to as 'wheel horsepower' or simply WHP. Two other qualifiers, originally developed for steam engines as an approximate indication of power, but which have fallen out of use due to their inaccuracy are: Nominal.

The term 'nominal HP' or 'nominal horsepower' is a theoretical calculation of the horsepower based on the engine size and piston speed. As such it is a calculated value rather than a measured value, with the result that it is imprecise and consequently has fallen out of use. Indicated or Gross. Like nominal horse power, indicated horsepower or gross horsepower is an estimate based on engine calculations. The actual power may be only 70% to 90% of the estimated power. Standardization As the above discussion on 'point of measurement' shows, the engine rating in HP varies depending on where the measurement is done. The values can also be affected by other variables such as temperature or atmospheric pressure, which affect the combustion efficiency of the engine. Furthermore, in the case of 'true horse power', the figures will be affected depending on how many optional accessories are being used. Consequently, depending on the test conditions, the resulting figures can vary. To ensure consistent measures, especially between different manufacturers, a number of organisations have developed a set of standards which define exactly how horsepower should be measured and under what conditions.

These include the Society of Automotive Engineers (SAE), the German Deutsches Institut für Normung (DIN), the Economic Commission for Europe R24 (ECE R24), 80/1269/EEC, the International Standards Organisation (ISO), and the Japanese Industrial Standard D 1001 (JIS D 101). Measurement values based on these standards may include the standard abbreviation to indicate the basis of the measurement. For example, 'SAE Net Horsepower' is a calculation of 'Net Horsepower' (see above section 'point of measurement'), corresponding to the SAE measurement standard. Inventor James Watt Biography Inventor: James Watt Criteria; First practical. Entrepreneur. Birth: January 19, 1736, in Greenock, Scotland Death: August 19, 1819 in Heathfield, England Nationality: Scottish Invention: steam engine improvements in 1769 Function: noun / steam engine Definition: An engine that converts the heat energy of pressurized steam into mechanical energy, especially one in which steam drives a piston in a closed cylinder.

Patent: Milestones: 1754: Learned the trade of mathematical-instrument making in London before returning to Glasgow 1763: Repaired a Newcomen steam engine, started him thinking about ways to improve the engine. 1767 Iinvented an attachment that adapted telescopes for use in measurement of distances 1769: Patented separate condensing chamber for steam engine. 1774: Started a business with Matthew Boulton to manufacture his improved Watt steam engine. 1781: Converted reciprocal engine motion to rotary motion. 1782: Invented double-acting engine. 1784: Patented a steam locomotive. 1788: Adapted centrifugal governor for use on the steam engine. CAP: Watt, James Watt, Thomas Savery, Thomas Newcome, Matthew Boulton, John Roebuck, ARY, steam engine, Newcomen's engine, watt, horsepower, industrial revolution, SIP, history, biography, inventor, invention. The Story: James Watt, Scottish inventor and mechanical engineer, renowned for his improvements of the steam engine.

Watt was born on January 19, 1736, in Greenock, Scotland. He worked as a mathematical-instrument maker from the age of 19 and soon became interested in improving the steam engines, invented by the English engineers Thomas Savery and Thomas Newcomen, which were used at the time to pump water from mines. Watt determined the properties of steam, especially the relation of its density to its temperature and pressure, and designed a separate condensing chamber for the steam engine that prevented enormous losses of steam in the cylinder and enhanced the vacuum conditions. Watt's first patent, in 1769, covered this device and other improvements on Newcomen's engine, such as steam-jacketing, oil lubrication, and insulation of the cylinder in order to maintain the high temperatures necessary for maximum efficiency. At this time, Watt was the partner of the British inventor John Roebuck, who had financed his researches. In 1775, however, Roebuck's interest was taken over by British manufacturer Matthew Boulton, owner of the Soho Engineering Works at Birmingham, and he and Watt began the manufacture of steam engines.

Watt continued his research and patented several other important inventions, including the rotary engine for driving various types of machinery; the double-action engine, in which steam is admitted alternately into both ends of the cylinder; and the steam indicator, which records the steam pressure in the engine. He retired from the firm in 1800 and thereafter devoted himself entirely to research work. The misconception that Watt was the actual inventor of the steam engine arose from the fundamental nature of his contributions to its development. The centrifugal or flyball governor, which he invented in 1788, and which automatically regulated the speed of an engine, is of particular interest today. It embodies the feedback principle of a servomechanism, linking output to input, which is the basic concept of automation. The electrical unit, the watt, was named in his honor. Watt was also a renowned civil engineer, making several surveys of canal routes. He invented, in 1767, an attachment that adapted telescopes for use in measurement of distances. Watt coined the term horsepower. Watt died in Heathfield, England, on August 19, 1819.

By the time he died, he'd changed history and was the most honored engineer who had ever lived. TO LEARN MORE Explaining the Fundamental Measures of Engine Performance in Plain English By Joe Pettit This is the first installment of a new series in Sport Truck devoted to bringing new enthusiasts up to speed on technical issues that tend to get distorted in the translation from engineers to our enthusiast readership. The present installment is a good case in point. We all use horsepower and torque, and for the most part we believe we know what these terms mean. But how accurate is that belief? What is the difference between a foot-pound and a pound-foot? And what does a foot-pound have to do with horsepower? We'll examine and explain this and other technical concepts in this series in easy to understand terms. In addition, we'll include real world, useful applications of this information. For example, as we explain in our current offering, there are specific areas of an engine you can alter to increase the power and force output of an internal combustion engine. Once you're aware of those, then you can make educated changes to your engine combination that will actually give you the desired result. We hope you find the information entertaining, informative, and useful.

to understand horsepower and torque, we need first to understand a few concepts used in developing the units of horsepower and torque. These are the concepts of mass, force, work, power, and, yes, torque. Mass: Mass is essentially the measure of how much matter is in an object. To find the mass of an object, you can divide its weight by the force of gravity or multiply its mass by the force of gravity to get its weight. Now that we've introduced the concept of force in order to explain mass, it's time to explore the concept of force. Force: Just as we used force to help define mass, we'll use mass to help define force. We already discussed the relationship of weight to mass as the application of the force of gravity to a mass. There are two points of interest about the force of gravity that will help us understand both mass and force. First, the force of gravity pulls you toward the center of the Earth, and second, that force is proportional to your mass. The more matter you contain, the greater the force of Earth's gravity on you. In other words, the more massive you are, the more you weigh, at least when you're near a monstrously larger mass such as a planet or a moon.

Weight is a measure of the force of gravity. Another way of looking at it is that force causes acceleration. When you put an object on a scale, it applies a force to the springs in the scale compressing them. The amount of compression is an indication of the force exerted on the mass. These observations are so obvious that their importance were overlooked for millennia until Isaac Newton formulated these relationships into his Second Law of gravity, from where the concepts of horsepower and torque come from, as well as much of the mechanics that govern the performance of your machine. Newton's Second Law states that the acceleration (A) of an object is directly proportional to the force (F) applied, and inversely proportional to the object's mass (M). In other words, the more force applied to an object, the greater the rate of acceleration. Also, the more massive an object the lower the rate of acceleration. Newton's Second Law is best known as an equation: F = MA, or force equals mass times acceleration. Work: The definition of work is the application of a force over a distance. In order to make the concept of work a measurable and useful term, the distance only counts if it is in the direction of the force you apply.

For example, lifting a 10-pound weight and putting it on a rack is an example of work. The force is the weight (10 pounds) and the distance is the height of the rack from the floor. If you lift the weight, carry it across the room, and put it on a rack, technically you haven't done any more work because the force of gravity is vertical and the transit across the room was horizontal. The foot-pound, or ft-lb (distance times force), is the unit of work (it's also the unit of energy because work and energy are very similar) in the English gravitational system of measurement that we use. It is the work done by a force of 1 pound applied through a distance of 1 foot. So if you lift a 1-pound weight 1 foot, you've done 1 foot-pound worth of work. If you lift 2 pounds 2 feet, you've done 4 ft-lb of work. The term foot-pound also designates units of torque. As a convenience, engineers typically reverse the order of the torque unit to pound-foot in order to distinguish it from the work unit.

The order, foot-pounds or pounds-foot, doesn't matter because the terms are multiplied (2x1=1x2) and therefore equivalent. Torque: Torque is a force that causes objects to rotate, spin, or turn. Any time you tighten a nut with a wrench you generate torque. As we just discussed above, the unit of torque is pound-feet. Just as with units of work, torque units contain quantities of distance and force. You can calculate torque by multiplying the force by the distance to fulcrum. Using the example of a wrench, if it is 1-foot long and you put 100 pounds of force on it, you are generating 100 lb-ft of torque. A 2-foot wrench requires only 50 pounds of force at the end to generate 100 lb-ft of torque. Power: Power measures how fast work is done. Generating 100 lb-ft of torque using a 2-foot-long wrench is relatively easy, but could you keep that force applied spinning the wrench at 4,000 rpm? That's what your truck's engine does. So power has a work unit (force times distance) divided by a time unit.

For example, 1 hp is 33,000 foot-pound of work each minute. Horsepower: What is it? Horsepower is a term invented by the engineer James Watt. In his capacity as an engineer in England, he needed a way to calculate the power available from horses for work. His measurements determined that, on average, one horse exerted a 180-pound force on a 12-foot lever attached to a capstan that it walked around. The distance around the circle (circumference) was a little more than 75 feet, and the horse made 2.4 revolutions per minute for a speed of about 181 feet per minute. Multiplying the 180-pound force exerted by the horse by the distance traveled in one minute gave him 32,580 ft-lb per minute, which he then rounded up to 33,000 foot-pounds of work in one minute to be his measure of 1 hp. To help you get your head around this, think of it this way: According to Jimmy Watt, one horse can do 33,000 foot-pounds of work every minute.

That means a horse generating 1 hp can raise 330 pounds 100 feet in one minute, 33 pounds 1,000 feet in one minute, or 1,000 pounds 33 feet in one minute. It doesn't matter what combination of feet and pounds; as long as the product equals 33,000 foot-pounds in one minute you have 1 hp. You can even express horsepower in ft-lb/second by dividing each term by the 60 seconds in the minute. When you do that you find that 1 hp equals 550 ft-lb/second. It's in this form that horsepower is most conveniently calculated from engine torque. Here is the equation that calculates engine torque: HP=RPM x Torque/5252 Horsepower: How To Get It As described in the equation above, engines generate horsepower by the pressure in the combustion chamber acting on the piston top to force it down the bore in order to make the crankshaft spin. This generates a torque force that allows work to be done at a rate dependent on the engine's speed and the magnitude of the torque.

Looking deeper into the formula for horsepower, we find there are four variables that contribute to the power generation in an internal combustion engine. They are: · Mean effective pressure acting on the piston top. · The stroke length of the crankshaft. · The square area of the piston top. · The number of power strokes per minute. The following equation explains and shows the relationship of how these variables influence horsepower output of a four-stroke internal combustion engine: HP= MEP x CID x RPM/33,000 x 12 x 2 Here's a quick explanation of the relationship of the values of this formula. MEP is the theoretical mean effective pressure acting on the piston top through its stroke. Notice that cylinder pressure is divided by the work of 1 hp (33,000 ft-lb). These are the force units. Cubic inch displacement (CID) reflects piston top area and the crankshaft's stroke length, which is divided by 12 to convert the value to feet. And finally, the number of power strokes per minute for a four-stroke engine is the term RPM/2 because the cylinder fires every other revolution. This equation predicts theoretical horsepower, not brake horsepower.

It does not account for the frictional power losses of the engine. When you measure on an engine dyno, you measure the net power output of the engine after all losses. The reason it's good to know the math and physical reasoning behind power generation is that it shows you exactly where to make changes to improve the performance of your engine. If you work with the equation, you'll see that to increase power output you have to increase one of these variables. In other words, you have to increase the mean effective pressure in the cylinders, the stroke, the bore size, or the engine speed. The most common approach is to increase cylinder pressure in order to increases torque output. To do this you need to add more air and fuel to the combustion chamber and ignite it. That's why tuned intake manifolds, superchargers, turbochargers, and nitrous systems work and part of the reason free-flowing intakes and exhausts work as well. Another popular way to obtain more horsepower is to build a bigger engine. The same cylinder pressure acting on a larger piston surface or through a longer stroke will make more power.

And finally, you can choose components that will allow your engine to spin very quickly, producing more power strokes per minute in order to increase power. This approach requires tuning the intake and exhaust flow capability to be tuned so the cylinders have enough fuel and air to generate adequate torque at high engine speeds and tends to reduce torque and power at lower engine speeds. Going From Torque To Horsepower Torque is a force that we measure through the distance of a lever arm. But four-stroke internal combustion engines have to spin to make torque and, more importantly, they have to spin in order to do any work, moving your rig down the road for example. The equation that describes the relationship of force at the flywheel, engine speed, and work expressed as horsepower follows: Torque= (5252 x HP)/RPM What is of interest is the conversion factor 5252. We reach that number when we divide Watt's 33,000 ft-lb/minute of work by the distance that the end of a 1-foot lever arm travels in one revolution of the engine, which happens to be 6.2831 feet.

When we divide 33,000 ft-lb/minute of work by the distance of our lever arm for measuring a force (torque), we're beginning to convert force into power. To define power you need a time unit. The time unit is supplied when we factor in the engine speed in revolutions per minute (rpm). This is how the equations that describe horsepower and torque convert the constant force at the end of a 1-foot lever arm (lb-ft of torque) into a measure of how fast work is done (horsepower). They were generated in a PC Dyno using stock heads and camshaft.

355 4.030 x 3.480 393ftlbs@3000rpm 303hp@4800rpm 377 4.155 x 3.480 413ftlbs@3000rpm 305hp@4800rpm 383 4.030 x 3.750 425ftlbs@2000rpm 301hp@4200rpm 406 4.155 x 3.750 452ftlbs@2000rpm 301hp@4000rpm Higher performance cam and heads.

355 358ftlbs@4500 361hp@6000 (340@5000) 377 375ftlbs@4500 364hp@5500 383 376ftlbs@3500 361hp@5000 406 391ftlbs@4000 363hp@5500 What is really clear from looking at these number is more cubic inches make more power Here is the biggest small block I build 434 408ftlbs@4000 360hp@5000 You will see a bigger bore makes more horsepower and a longer stroke makes more torque. The differences are small but can be increased with further up grades.

Going from a 355 to 383 added 28cid 32ftlbs & 0hp on a stock motor and 18ftlbs & 0hp on a big cam/head combo The 377 added 22cid 20ftlbs & 2hp and 17ftlbs & 3hp In the real world we make a little more power than these numbers because the camshafts and heads are better than those in the computer simulation dyno. But you will see the increasing the bore size increased horsepower where as stroke increased torque. The reason 377s are used in sprint cars are a maximum cid rule, and higher RPM motors make more horsepower, and these cars operate at higher RPMs. Using a 383 would not be taking advantage of the stronger torque because the engine would be revving too fast, and as a result not making enough torque or horsepower.

To exaggerate the bore/stroker torque/horsepower relationship look at this motor 330cid 4.185 x 3.00 372ftlbs@3500 307@5000 stock 497ftlbs@6000 640@8500 everything thrown at it 377 with everything 540ftlbs@5500 630@8000 From this illustration you can see that short stroke motor likes RPM and the extra RPM makes more HP not Torque.

Question: Which engineer first used the term Horsepower?
Answer: (James) WATT