Talk:Horsepower/Archive 2

Hydraulic Horse Power?
Only the formula is present and the explanation is absent. Unfortunately I've no idea of the explanation and I request someone to post it. (Krishvanth 17:14, 11 October 2007 (UTC))


 * I've explained it some; it doesn't belong as a different unit. It is merely a trivial, particular method for calculating normal mechanical English-units horsepower, using flow rate in U.S. gallons per minute and pressure in pounds force per square inch (lbf/in²).  The 1714 figure actually comes out to be 17142&frasl;7, or 12000/7.  All you need to know to figure that out is that there are 33,000 lbf·ft/s in a horsepower, 12 inches in a foot, and 231 cubic inches in a United States gallon.  Cancel out units as appropriate (it might help you to write out as fractions with a vertical bar):


 * (1 gal/min)(1 lbf/in²)(231 in³/gal)(1 ft/12 in)(1 hp·min/(33,000 ft·lbf)) = 7/12000 hp


 * For SI units, all you need to do is multiply flow rate in m³/s times pressure in Pa to get power in watts. Gene Nygaard 02:45, 14 October 2007 (UTC)

SAE Gross Horsepower - too much information?
What's currently listed as section 2.2.1, "SAE Gross Horsepower", seems to contain quite a bit of information not at all related to any definition of horsepower. Not that I don't find it interesting (I do), but IMO the information about exaggeration of ratings by manufacturers, allowed engine modifications, etc. doesn't belong in this article. --140.179.169.70 (talk) 18:56, 23 January 2008 (UTC)

Redirect
Shouldn't this page redirect to the Hewlett-Packard article? Marshall T. Williams (talk) 17:34, 2 August 2008 (UTC)


 * If you mean hp, then no, a standard abbreviation should redirect to its spell-out. —C.Fred (talk) 17:56, 2 August 2008 (UTC)

ESHP - Equivalent or Effective?
I am currently becaming more and more confuse with definitions of ESHP: does this stand for Equivalent Shaft Horse Power or Effective Shaft Horse Power? Please note that "Horsepower" entry at wiki simply do not mention the first one (equivalent), and defines that "E" as Effective, only. In other hand, Pratt & Whitney manufacturer and FAA certification data sheet for its engines mention the term "Equivalent" for ESHP (see PDF doc at reference #26 on "Pratt & Whitney Canada PT6" entry). Equivalent to what, after all?

I would like to see a light on this subject, and - at the same time - some coherence between both entries. Can somebody explain that tiny letters? (PS - I placed the same discussion topic on "Pratt & Whitney Canada PT6" entry) —Preceding unsigned comment added by RobertoRMola (talk • contribs) 18:51, 9 October 2008 (UTC)

Sears or marketing horsepower
I'd like to find a good reference that talks about the way certain consumer power tools are sold with rather arbitrary horsepower ratings - it's not uncommon to find a "5 HP" compressor that plugs into a standard 15 Amp 120 V wall outlet. The same is true of, say, consumer woodworking tools. These must be rated on the same basis as those " 50 watts/channel PMPO" speaker sets for computers that run off a USB port, or the "500 watt" home theater system whose nameplate says "1.5 amps 120 volts". But this article should be more about the units themselves, and less about applications of the units (which belong in the automobile articles, or possibly under Consumer fraud, etc. There'd be less confusion about units in general if our advertisers were more honest.  --Wtshymanski (talk) 03:56, 6 February 2009 (UTC) "- Where units of horsepower are used for marketing consumer products, often measurement methods are designed by advertisers to maximize the size of the number produced for any product, even if this may not reflect realistic capacity of the product to do work when used in normal conditions." We need a referenced way to get this into the article.  It would be useful for consumers to understand when they are being lied to. --Wtshymanski (talk) 18:54, 10 November 2009 (UTC)

Introduction and tag
So the introduction was a bit terse. I've tried to ease the transition. However, it looked good compared to the introduction for Metre, which starts off well and then by the end of the opening paragraph is raving about something called a "quantum vacuum". Asking the Wikipedia to explain anything is as risky as asking the local cat lady to explain anything... they start off sensibly and then watch out! --Wtshymanski (talk) 18:52, 6 February 2009 (UTC)

Wary of conversions
7 psi is not 50 kPa. It's pointless rephrasing the historical definitions of horsepower in SI units because the definitions didn't use SI. --Wtshymanski (talk) 17:55, 11 September 2009 (UTC)
 * I didn't rephrase the historical definitions. 7 psi conversion corrected. SkyBonTalk/Contributions 05:06, 12 September 2009 (UTC)

No evidence the term was coined by Watt
The earliest recorded use of the term in the OED is 1807, after Watt retired. http://www.sizes.com/units/horsepower_british.htm says Boulton and Watt would refer to a 10-horse engine, not 10-horsepower engine. His contribution was determining the approximate physical power of one horse to use as a comparative unit that would be understood by his contemporaries. William Avery (talk) 21:53, 7 January 2010 (UTC)

Factory Pro commercial web site is not an independent, reliable source.
The citations to Factory Pro's web site are not reliable. See discussion at Talk:Yamaha YZF-R1. It boils down to competing claims between Factory Pro and their competitor Dynojet. No independent sources support Factory Pro's claims that their product is superior. The citations should be deleted as spam, unless anyone can cite evidence that the company's site or their claims are reliable. Their claims are probably fringe theories and WP is being used to right great wrongs. That is not OK. --Dbratland (talk) 19:41, 5 May 2010 (UTC)

They are reliable, but not up to Wikipedia standards per COI. Your continued claims that some product or another is better is a fantasy. There is one scale that is "hp" as delivered and there is another scale that is consistently higher than the measured hp by a "magazine reported" 5% to 10% to whatever some journalist "expert" decided to write in a story that contained information about inflated horsepower numbers. Here are print references that are available in the published referencing why "dynojet scale" horsepower is not "hp" as defined by any reputable engineering source, including Wikipedia and virtually any encyclopedia.

I guess that the only defense that one could come up with is with some print article providing dynojet's proprietary algorithm - something better than what you quoted before - something like our dynos are correct and dynojet's sold more dynos than Factory Pro, from a magazine who's race team is sponsored by dynojet. That fact that their team is sponsored by dynojet is an inexcusable oversight for wikipedia.

Articles citing dynojet's hp inflation have been posted on several talk pages and still there is a problem.

These print articles provide Wikipedia valid proof. They are all copied to my website, but all reprints of your requested "acceptable" proof.

http://www.factorypro.com/magazine/Motorcycle_Consumer_News,%20may%202009,%20Measures,%20djhp/Motorcycle_Consumer_News,Searle,Measures,Dynojet,Oct,2009.pdf

http://www.factorypro.com/magazine/Cycle_Canada,dynojet%20Inaccuraccies/mag_cyclecanada_Dynojet_dyno.html

http://www.factorypro.com/magazine/Sports%20car%20International%20magazine/dynojet_dyno_inflated_hp_reason,SportscarInternationalHartman.html

http://www.factorypro.com/magazine/Sportrider,%20Ramair%20part%202/mag_sportrider,RamAir,part2.html

Every reprint is a reputable periodical, as you requested. I've provided the necessary proof. You fix the hp, djhp and bhp errors in the articles.

This is a ridiculous argument - almost every experienced and informed person in the motorcycle industry and without exception every person in the dyno industry (except most dynojet employees) knows that dynojet horsepower is inflated over true or effective horsepower. Geez - this is as bad as the R1 Forum...... :-)

Best regards - Marc Salvisberg (talk) 05:48, 11 May 2010 (UTC)


 * So we agree that what you are attempting to do -- publicize your company's opinions with sources that fail the standards for reliable sources -- violates Wikipedia's policies. I'm not going to keep feeding the discussion with you about what these magazine articles say.  As discussed elsewhere, your characterization of these articles is consistently inaccurate.  Some sources have pointed out flaws in Dynojet's system.  No sources have expressed any agreement with Factory Pro's claims.  Nobody but Factory Pro says "true horsepower."The bottom line, as always, is whether the edits meed Wikipedia's policies of verifiability.  And we have consensus that this marketing material from Factory Pro does not meet that standard and so should be deleted. --Dbratland (talk) 16:59, 11 May 2010 (UTC)

Reprint from Karting magazine: true horsepower http://www.land-and-sea.com/dyno-dynamometer-article.htm

true horsepower http://www.experiencefestival.com/a/Horsepower_-_RAC_horsepower_taxable_horsepower/id/1482114

effective horsepower http://www.ytmag.com/articles/artint142.htm

effective horsepower http://youtractor.com/blog/uncategorized/everything-you-need-to-know-about-horsepower/

effective horsepower http://www.acronymgeek.com/EHP/Effective_horsepower_in_physics/12314

effective horsepower This section is from the book "Wrinkles And Recipes, Compiled From The Scientific American", by Park Benjamin. Also available from Amazon: Wrinkles and Recipes, Compiled From The Scientific American. "2. The net or effective horse-power of an engine is computed from the useful resistance overcome. If, in the preceding example, the pressure on the piston, after deducting that required to overcome the friction of the engine, is 3200 lbs., the effective horse-power is 2200 times 400, divided by 33, 000, or 26.7." http://chestofbooks.com/crafts/scientific-american/Recipes/Different-Kinds-Of-Horsepower.html

effective horsepower reprint from the 1920's http://books.google.com/books?id=RWgrAAAAMAAJ&pg=PA1122&lpg=PA1122&dq=effective+horsepower&source=bl&ots=xEOjT3i6ct&sig=HQYqYug4QAsKccjxfk1BiLJOobA&hl=en&ei=AUPqS4TCC4uosgOT6Iz5Bw&sa=X&oi=book_result&ct=result&resnum=10&ved=0CDsQ6AEwCTge#v=onepage&q=effective%20horsepower&f=false

effective horsepower and /prony brakes http://www.buckleyoldengineshow.org/Spotlight/Horsepower-Testing-Pony-Brake

effective horsepower on a sled http://www.mcbperformance.com/xlr8.html

Nascar effective horsepower http://autoracingsport.com/toyota-has-horsepower-advantage-at-daytona/

true horsepower as related to RAC http://www.2carpros.com/how_does_it_work/horsepower.htm

and finally, a 1974 US issued patent relating to "true horsepower" and drive wheels and chassis dynamometers. http://www.freepatentsonline.com/3930409.html "Description:

This invention relates to dynamometers and more particularly relates to vehicle chassis dynamometers for accurately determining the true horsepower available at the drive wheels of a vehicle. A chassis dynamometer may be generally classified as a shop vehicle testing apparatus for measuring the power available at the drive wheels of a vehicle. The horsepower is determined by measuring the speed of the wheel, generally through a contacting roll, and the torque thereof. Then if electrical signals are derived proportional to each, the horsepower may be calculated by a well known equation and implementing circuitry.

True vehicle wheel or road horsepower is influenced to an appreciable degree by vehicle rolling resistance, drive line efficiency and vehicle weight. All of these factors produce a horsepower loss that must be considered in determining the true engine flywheel net horsepower available. An evaluation of vehicle performance is accomplished by comparison of the horsepower developed by the engine, and the delivered horsepower to the drive wheels."

Marc Salvisberg (talk) 06:52, 12 May 2010 (UTC)


 * Awesome. I have no complaints except when you start touting Factory Pro and taking digs at your competitors, or when you cite sources that don't verify what you wrote in the article. If you can find some way to talk about this subject without marketing your company's wares, go ahead.  You should consider, however, as WP:COI explains, it is terribly difficult for any mere mortal with a personal stake to write objectively.  You might be happier editing articles not in a field where you have merchandise to sell, so that you can be neutral. --Dbratland (talk) 23:33, 12 May 2010 (UTC)

Thanks -

But it seems that you deleted the entire "Effective Hp, true hp (chassis dyno)" section which is "true hp" as the patent citation indicates and was originally here, even before me.

I'm assuming that a "dynojet hp (chassis dyno)" header would be ok if it had no explanation and just citations, (none of which written by me)? Let someone else fill in the description. You can even write the text, by now. The dynojet "hp factor" is usually described as a "fudge" factor or "inflated" by the valid magazine references - you can see that even just quoting publications makes it appear that I'm taking so called "digs" at a competitor. "Fudge factors" and "inflation" are usually taken as negatives when performing measurements. Much to everybody's chagrin, it's an "inconvenient truth" that what's loosely written as "hp", may or may not be the same "hp".

Hp used to be James Watt's hp, now, in wiki and magazines, it's not. (or it might be, you never know unless it's qualified).

Best regards, off to he AMA races to see who M4 work is....... Rooting for local racer Lenny Hale and Cory West and Steve Rapp in the 600 race. Marc Marc Salvisberg (talk) 20:37, 15 May 2010 (UTC)

Horsepower ratings
I know that the horsepower ratings for vintage cars is very different from the modern BHP rating. For example the 9hp 2CV engine was not a tenth of the power of a modern small car, but probably about a third.

Does anyone know how these horespowers relate to BHP?

-- [[User:Chris Q|Chris Q]gfjhjhfgh] 12:32 Sep 17, 2002 (UTC)

See tax horsepower -- Egil 23:29 Apr 24, 2003 (UTC)


 * Would it be reasonable to try and add in a more comprehensive note about how these things have changed, to e.g. the French system subheading? Right now it has a note about the 2CV, and shows the modern method of calculating the tax band (which does at least explain why French cars appear to standardise on certain seemingly-abitrary power outputs regardless of their actual CC or CO2... 52, 59, 68, 80, 92, 106hp, etc... or just under 1.0, 1.2, 1.5, 2.0, 2.4, 3.0 tax-HP...), but that doesn't make any sense when putting one in the context of the other. A mid-late model 2CV-4, with the highest power/capacity to still qualify as an actual "2CV", would only count as having one-half tax HP (26 true HP = 19.4 kW = 0.48 tax hp), and an early 2CV-6, noted as "now technically counting as a 3CV", would be even lower (21 true hp = 15.6 kW = 0.39 tax hp). Obviously the system has changed so much as to be worthy of mention to avoid confusion owing to this? As far as I can tell, it was originally based on cylinder dimensions much like the RAC system (though not -exactly- so... otherwise the "2CV" with a 62mm bore (2.44") and 66mm stroke would actually have been a 4 or even 5 CV: (2.44 x 2) / 2.5 = 4.77 RAC HP, and supposedly rounding errors made about a 1.7% difference in one direction or the other (4.69 ~ 4.85 RAC HP)), and later was tweaked to take account of stroke (i.e. overall CC instead of just piston-head area) and peak RPM (thus being a closer account of engine output, though still not paying attention to improvements in efficiency from the overall design or from use of higher CR and high-octane fuel).


 * However it worked, we have a pre-war and early post-war design with two 62x66mm combustion chambers (375cc), then a twin 66x66 (425cc) and twin 68.5x59 (435cc) all being "2CV", and then 74x70 (602cc) and 74x76 (652cc) designs being "3CV"... maybe it ended up being roughly 220cc per CV, with the evolved design's 5750rpm peak power? (Quite how that fits with the final 425's 6750rpm, I don't know... basing it off peak torque wouldn't work either, as one was 2400 and the other 4000...) 87.115.98.16 (talk) 09:46, 1 September 2012 (UTC)

Why use watt instead of horsepower?
The other day, I added some words, but they have been removed again.

I think it helps to clarify two things right from the beginning:
 * horsepower is a unit of power which is energy per unit of time. IMHO the italicised text is an essential part of the definition.
 * Why abandon the familiar horsepower in favour of watts? Two reasons:
 * watts are part of a system of units which is a benefit for physics calculations
 * horsepower slightly differs by geographical latitute because it is based on an incorrect understanding of physics, confusing weight and mass.

I think WikiPedia lemma's should state the essentials right at the beginning. History is relevant, but not part of the essence, in my opinion. Rbakels (talk) 14:50, 23 August 2010 (UTC)

Directive implementation
I guess the (very) late implementation of EU Directive 80/181/EEC is UK only? Ireland? When was it implemented in continental Europe? Rbakels (talk) 14:57, 23 August 2010 (UTC)

Horsepower from a horse
The section "Horsepower from a horse" is very incomplete: the most pressing issues here are: "What type of horse was a brewery horse? In England at the time a work horse most likely would have been one of the three British "heavy breeds" – the Suffolk punch, the shire horse, and the Clydesdale. The Clydesdale is said to have originated in the latter 1700s, perhaps too late to be a common work horse at the time Watt was doing his horsepower calculations. So it seems likely the horse in question was either a Suffolk punch or a shire horse." --> so it would appear that it's either a Suffolk punch or a shire horse; however at
 * What kind of draft horse are we talking about here ? Searching a little on the net we find:

http://boards.straightdope.com/sdmb/showthread.php?t=546109 we find: "I've gotta say that I think James Watt was a bit off on his calculations, or perhaps he was using a mini-pony. My team of Belgian draft horses (that's two horses) is roughly capable of doing half the work of my old Ferguson 30hp tractor, which would mean that each horse can crank out about 7hp on a sustained basis. Assuming a relatively constant ratio of work potential to weight, Mr. Watt's horse would weigh less than 300lbs. But since he was in the business of replacing horses, it was to his advantage to minimize their stated capabilities."

and at http://www.theoildrum.com/node/6287 we find:

"David, I think Watt used an average horse, not a draught horse, and it was a rate of work that could be sustained all day by said horse. I think you will find the horsepower of an old steam tractor to be more accurate. A 5hp steam tractor would probably come pretty close to five of your horses. The old Fergies are great little tractors, but I doubt you woud be getting your 30hp out of it today. Also, by the time you get to drawbar power, after gearbox etc, and wheel slip, you only get about 80% of what engine puts out. The horse was measured by what it put, but it's lungs ("engine") can probably operate at 1.5 hp."

so, either it's a shire horse of suffolk punch (none of them are even the strongest horses I believe), or it's even an average horse. Also, it seems that some estimate regular draft horses to have 1.5 HP of power for "sustained" work. That leaves allot of room of suggestion, ...


 * Another issue is the "sustained work"; what does this mean ? Is that 8 hours of work, more like 12, ... (750W x 8 = 6000W, 12 x 750 = 9000 W, quite the difference).


 * Finally, I don't really get how it's possible that 1 horse would pull but 6 tons, and 2 horses 36 tons (see http://wiki.answers.com/Q/How_much_can_one_horse_pull_vs_2_horses ) Howcome this isn't lineair (ie 6 tons for 1, 12 tons for 2 horses, or 18 tons for 1, 36 tons for 2, whatever the case)

Finally, perhaps that we can provide a small comparison between the strongest and weakest draft horse breeds, ie would say a Russian Draft Horse be able to pull much more than ie a Suffolk punch/Shire ? (ie 1,9 HP vs 1,5 HP ) ? Also, I wonder how much HP say an ox can pull (see Plough.

91.182.195.113 (talk) 12:31, 26 November 2010 (UTC)

British horsepower
''The abbreviation bhp may also be used for British horsepower[15] (though the usual use is brake horsepower), defined as 33,000 lb·ft/min. The description of the unit "British horsepower" is used when differentiation from "metric horsepower" is required.''

I am removing this section because it seems to me to be highly suspect. I don't think there is any such thing, and don't think this (which I have left in the article) can be regarded as a reliable source, at least not for this bit of nomenclature. BHP is usually brake and sometimes boiler but not British, surely? If anyone can provide better references I will be happy for the section to be reinstated. Globbet (talk) 09:04, 26 August 2011 (UTC)


 * AIUI, this was a genuine name for the unit, but it was horribly obscure and is long fallen from use - however the unit is still around and is in fact the source of the main hp definition. "Horsepower" in the sense of brake horsepower was first defined as sensible round-number units of either 550 foot-pounds/second (in the Imperial world) or 75 mkgf/s (in the metric world, usually the French CV or German PS). All of these are close enough to be considered equal, within the measuring accuracy of anything pre-electric.
 * For a while afterwards (WW2 era?) they were separate units of slightly different quantity and needed to be identified separately, as they were now within the precision that could be distinguished by measurement.
 * With the move to SI base units for British measurements ('70s?), the horsepower in Britain was redefined as an arbitrary integer number of SI units and so the hp was rounded up to the well-known 746W figure of today. "British horsepower" then created a new name for an existing legacy unit, with no purpose other than this legacy, and remained based on 550 foot-pounds, with an actual value slightly less than 746W. Its only real function was in updating textbooks - the "550 hp" and "746W hp" were (deliberately) both within the measuring precision of the time, for nearly all physical measurements. Andy Dingley (talk) 09:53, 26 August 2011 (UTC)
 * It would be nice to have a citation for the change in definition of the horsepower in Britain from 550 ft lb/s to exactly 746 watts. I'm not sure what "time" you're referring to; the first definition of the metre was valid to about 5 significant figures, in 1795. I'm sure metrologists of the time wouldn't whack off a trailing digit just for fun. Watt couldn't have defined his unit as exactly 746 watts because the SI system didn't exist yet; I'm not sure why "33000" was considered a preferred number, since the precision of mesaurements of actual horses evidently could have justfied, oh, say, 30000, an even "rounder" number. All the tables I've seen call a horsepower 745.699 watts except for the rating of electric motors when it is rounded out to 746 watts (good enough for slide-rule calculations), in such publications as NEMA standard MG-1. If you're converting to SI anyway, why make up a new unit based on a non-power-of-10 multiple of an SI unit and give it the name of an old unit?  It'd be like re-defining the inch as exactly 2.5 cm because you don't like dealing with 3 significant digits. Even British love of tradition must have limits? --Wtshymanski (talk) 14:20, 26 August 2011 (UTC)
 * Sorry, Wtshymanski, it is not clear to me exactly what you are saying. Globbet (talk) 19:59, 26 August 2011 (UTC)
 * I'm saying a British horsepower is a horsepower is 550 ft lb/s is 745 and change watts, and that the only reason the term gets used is to distinguish between 550 ft lb/s and 75 kg m /s definitions. --Wtshymanski (talk) 21:06, 26 August 2011 (UTC)

Nominal horsepower
There is a sort-of-relevant discussion going on at Template_talk:Convert - Globbet (talk) 21:27, 26 August 2011 (UTC)
 * If templates were smart enough to figure outthis sort of thing for themselves,we wouldn't need editors. Anyone remember User:Bobblewik? --Wtshymanski (talk) 17:52, 31 August 2011 (UTC)
 * That is pretty much in line with the conclusion reached there. I don't. Globbet (talk) 22:27, 31 August 2011 (UTC)

"Metric Horsepower"
There is no official measure of horsepower called "Metric Horsepower", only Americans call it this way. it is properly called "PS", and is based, obviously, on the German "Pferdestärke". This equals to ca. 0,735 kW, therefore 1PS = 1.36 kW (ca.). Also, the American Horsepower measurement (or is it the British one, I believe its called "SAE hp", and/or "bhp", which is 1.34 kW, is missing a detailed description here, how come?.--Daondo (talk) 22:36, 17 October 2011 (UTC)
 * Well, we've got a whole section titled "Metric Horsepower" which gives all these different metric horsepower units, ( those Europeans have different words for everything), and the rest of the article is talking mostly about 550 ft lbs/sec which is a British or Mechanical or SAE horsepower. You do know that SAE stands for Society of Automotive Engineers which isn't particularly British? --Wtshymanski (talk) 01:23, 18 October 2011 (UTC)
 * To make things more "interesting" in and in  I found PSi which probably means indicated PS. One more conversion problem. Peter Horn User talk 20:43, 17 October 2012 (UTC)

Contradiction in bhp definition
At the top of the Measurement section it says bhp is "power delivered directly to and measured at the engine's crankshaft", and if you subtract "frictional losses in the transmission" you get shp. Later it says bhp is power before subtracting the auxiliaries such as alternator and hydraulic pumps.

So shouldn't that first section say something like this? "Brake / net / crankshaft horsepower (power delivered directly to and measured at the engine's crankshaft) minus frictional losses in the transmission (bearings, gears, oil drag, windage, etc.), minus auxiliaries such as alternators and pumps, equals Shaft horsepower." Kendall-K1 (talk) 16:48, 21 February 2013 (UTC)

Globalize?
Why is there a globalize template on the "Current definitions" section? Isn't horsepower a US unit? Kendall-K1 (talk) 02:15, 22 February 2013 (UTC)

Mechanical horsepower conversion procedure - numerical precision
From the standpoint of error propagation I found silly that the original 2 significant digits (1 hp	≡ 33,000 ft·lbf/min) expand through the conversion into SI units to final 17 significant digits (= 745.69987158227022 W). Ignoring the precision of the conversion factors themselves and assuming 1% relative error, the final conversion should be something like 1 hp≡ 33,000 ± 330 ft·lbf/min ≡ 745.70 ± 7.46 W. Even taking the original number defined by Watt as a number of 5 significant digits, this brings an error in the order of 0.00746 W (relative error of 10^-5) which renders the tail of digits into a meaning less nonsense. — Preceding unsigned comment added by 82.208.33.113 (talk) 22:55, 15 April 2012 (UTC)
 * (months later) Well, definitions are (by defninition) exact, so Watt's "33,000" has as many sig figs as you need. As long as we're talking about "definitions" of units and interconversions between them the precision is as high as ever needed. But it is absurd to give the final result to more significant figures than could ever be possibly resolved in an actual measurement. Anything more than 6 figures is going to make the reader's eyes glaze over and doesn't really improve the effect of the presentation. --Wtshymanski (talk) 13:36, 21 August 2012 (UTC)
 * The value used for the pound-mass has an erroneous extra digit. It should be .45359237 kg exactly, not .453592376 kg.  And a full 5 digits of the final result, 745.699881448 W, are wrong.  The exact value denigrated above, 745.69987158227022 W, is correct.  Exact calculation in the definition of units avoids this sort of error.  — Preceding unsigned comment added by 208.53.195.38 (talk) 14:15, 17 July 2013 (UTC)

Historical symbol
A ligature-style symbol/glyph/character $$\mathrm{H\!\!P}$$ is used to denote 'horsepower units' in the book Aiba, S., A. E.Humphrey, and N. F.Millis, Biochemical Engineering. 1965, New York, U.S.A.: Academic Press. 333 pp.. (e.g. pages 167ff.). —DIV (138.194.12.224 (talk) 02:28, 22 March 2013 (UTC))


 * There is a unicode character ㏋ (U+33CB "square hp") but I can't find anything that says what it means or what it's used for. It's in the CJK compatibility block with other units of measure like mV, Hz, and gal, so it's probably horsepower. But it's not a ligature, it's two separate letters crammed into one glyph. Kendall-K1 (talk) 18:41, 4 April 2013 (UTC)

I welcome the article. My only comment is that I believe units of measurement named after those who helped define them have their first letter capitalized. (e.g. Watts, Amps, Joules, Faradays, Volts, etc.). If this is correct, the frequent reference to 'watts' should be corrected to 'Watts'. — Preceding unsigned comment added by 65.113.43.98 (talk) 22:39, 6 August 2013 (UTC)

use of funny f in the middle of units
There is a subscript f in the middle of many units that is undefined within this article, and its meaning is non-obvious. Feet? Force? Function? Can we define it the first time it is used? metaJohnG (talk) 02:22, 11 September 2014 (UTC)
 * Please, could you give us an example. I looked in the article and cannot find what you mean.--  Toddy1 (talk) 06:46, 11 September 2014 (UTC)
 * It stands for force -- i.e pound-force or kilogram-force. Pounds ARE a unit of force, but in lay usage pounds often denote mass (The amount of mass that experiences one pound of gravitational force at Earth's surface).  Hence, people who are using pounds but also being precise about what they mean will use the terms pound-mass or pound-force.  A kilogram-force is the force exerted by one kilogram of mass at Earth-standard gravity.

74.192.230.149 (talk) 21:47, 16 October 2014 (UTC)

About the history of the unit
The small change I've recently made is;
 * From:
 * This was rounded to an even 33,000 ft·lbf/min. Watt calculated the power as 33,000 ft-lb per minute.


 * To:
 * Watt defined and calculated the horsepower as 32,572 ft·lbf/min, which was rounded to 33,000 ft·lbf/min.

Somebody can also change instances of ft·lbf/min to lbf·ft/min, as in N·m, where force comes first and distance follows. There are many quantities with long units but if the order of individual units in these combined units keep changing from article to article, it ends up being inconsistent, and thus potentially confusing.

An excerpt from the previously cited reference is given below:


 * In 1783, James Watt created the term of “horsepower” to describe the power of the new movers. Watt defined one horsepower as the amount of work required from a horse to pull 150 pounds out of a hole that was 220 feet deep. Watts calculated the kinetic energy as 33,000 ft-lb per minute. Two horses together produced over thirty hp.

Do not cite these kind of references for the love of solar system.

If you don't know the difference between work and power, do not edit a \\//ikipedia article called horsepower, and as a digression, I'd also strongly advice against writing an MS thesis, or a thesis for any other degree, that will be approved. 85.110.3.29 (talk) 10:51, 6 December 2014 (UTC)


 * No we cannot change foot-pounds into "pound-foots". When people were using foot-pounds (and foot-tons), they expressed them as foot-pounds (and foot-tons).  They did not express them us "pound-foots".


 * As for your edit, it is of no value. I have reverted it.  Instead I have added another citation - to a source that is not behind a paywall, which can also serve as a citation for the statement that "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".


 * 85.110.3.29 made quotation from "the previously cited reference" - which reference was he/she referring to?-- Toddy1 (talk) 12:14, 6 December 2014 (UTC)


 * The source for the statement "Two horses together produced over thirty hp" was a thesis/dissertation for an MA thesis Delayed Obsolescence: the Horse in European and American Warfare from the Crimean War to the Second World War, and appears on page 6.  However the source cited by the MA thesis for that statement is a book that does not make the statement.  The reason the footnote explains this, was that well-meaning people such as yourself kept putting it into the article, and they needed to be told why it was being deleted.--  Toddy1 (talk) 12:24, 6 December 2014 (UTC)


 * Gee, making people understand a simple, tiny thing can be quite costly indeed. Especially when they try real hard not let other editors improve the article.


 * Okay read what I write this time, and read carefully. You do not seem to understand what I'm writing (probabaly as clearly as possible).


 * You said "As for your edit, it is of no value. I have reverted it. Instead I have added another citation...". The statement to which you added an additional citation is not even what I changed. So basically, you don't see a value in something that is not even what I changed. I hope you can comprehend this. In fact your revert is of no value, because you have done it without even understanding what the edit was, and why it was made.


 * This is the version you (strangely) insist on keeping: "Watt calculated the power as 33,000 ft-lb per minute.[12]". But this is not what the referenced material (i.e. the 12th reference) says. Let me repeat, here is the relevant excerpt from the reference that is still cited in the article:


 * "In 1783, James Watt created the term of “horsepower” to describe the power of the new movers. Watt defined one horsepower as the amount of work required from a horse to pull 150 pounds out of a hole that was 220 feet deep. Watts calculated the kinetic energy as 33,000 ft-lb per minute. Two horses together produced over thirty hp."
 * As you can see (hopefully), it says "Watts calculated the kinetic energy as 33,000 ft-lb per minute.". Firstly, ft-lb per minute is not even kinetic energy, and this says how messed up that reference is. Secondly, you can not write a sentence and make a citation for it, which is non-existent. I hope you can comprehend what I'm saying (in fact repeating) this time. That reference does not say "Watt calculated the power as 33,000 ft-lb per minute.[12]".


 * Now here is the funny point that seems to be troubling you: Nothing I have written so far, either in the talk page or in the article, has got anything to do with the statement "Two horses together produced over thirty hp". That sentence is quite funny, just like the rest of the statements I wrote above from the same reference. Can you also comprehend that? I understand your english may not be well enough to comprehend fast but given enough time you can comprehend what I'm saying.


 * Okayy, as for the suggestion of re-writing the unit as lbf·ft/min:


 * The article that explains the unit is Pound-foot (torque). As you can see, the name of the \\//ikipedia article is pound-foot, which actually refers to poundforce-foot, i.e. lbf·ft. And in the article, it is stated that "... foot-pound (ft·lb or ft·lbf) is also sometimes used interchangeably with "pound-foot" to express torque.". So, as I wrote up there the first time, it is not necessarily wrong, but inconsistent, considering articles like torque. If there is a combined unit like lbf·ft/min, using it as ft·lbf/min in some articles and as lbf·ft/min in some articles is inconsistent. Try to be consistent, because consistency matters.


 * P0S: I said "somebody can edit...", I've been editing for the last five years, which is possibly longer than you, therefore don't rush to speak as "we" as apparently we (you and I) can very well disagree.
 * 85.110.3.29 (talk) 13:12, 6 December 2014 (UTC)


 * You seem not to understand.


 * Horsepower is a measure of power. If you disagree with this, please say.


 * Power can be considered as energy per minute.


 * Foot-pounds and foot-tons are a measure of energy. (There is also a metric unit called a Joule that some people use for this.)


 * Therefore power can be expressed as foot-pounds (or foot-tons) per minute. (People who use metric units use Joules per second for this.)--  Toddy1 (talk) 13:28, 6 December 2014 (UTC)


 * Reference 12 in the article is Marshall, Brian. "How Horsepower Works". Retrieved 27 June 2012. As far as I can tell this reference does not contain the statement: "In 1783, James Watt created the term of “horsepower” to describe the power of the new movers. Watt defined one horsepower as the amount of work required from a horse to pull 150 pounds out of a hole that was 220 feet deep. Watts calculated the kinetic energy as 33,000 ft-lb per minute. Two horses together produced over thirty hp."-- Toddy1 (talk) 13:38, 6 December 2014 (UTC)


 * There are 1308 words (!) under this section uptil this post and you still don't know what you are talking about let alone making any progress in this redundant and ill-purposed discussion, which you can't seem to have enough of and which is not worthy of \\//ikipedia at all. Nothing I said so far got anything to do with the question of whether horsepower is a measure of power or not, which would (hopefully) be an unnecessary question. You are wasting your and others' time.


 * The field I work in is mechatronics, so I am supposed to have some idea about what I would say on horsepower, but the thing is I didn't even write anything new, I just combined two sentences and removed the problematic reference. But I have to tell that the article is still in pretty bad shape as it is.


 * Okayy, let me re-state (in fact repeat) the points you are missing for the third and the last time. Let's see if you can comprehend the items in the below list:


 * First of all, what I wrote in the beginning of this section already lists the 12th reference. And secondly, of course it is not the 12th reference in the current version of the article because it is removed with my edit, which is the edit you reverted without having any clue about.
 * This is the version you (strangely) insisted on keeping: "Watt calculated the power as 33,000 ft-lb per minute.[12]". But this is not what the referenced material (i.e. the 12th reference) says. Instead, it says: "Watts calculated the kinetic energy as 33,000 ft-lb per minute.". Firstly, the cited reference is a bad source of information because ft-lb per minute is not a unit of measure of kinetic energy but of power. And secondly, a \\//ikipedia article should not include a cited statement which does not exist in the cited material. Okay let me say it for the fourth time; That reference attached to the sentence you insist on reverting to does not have the string "Watt calculated the power as 33,000 ft-lb per minute.[12]" anywhere in it. So, do not insist on reverting to that version, it is wrong, you see? If you don't understand what I'm saying, get a help from one of your friends who understands English language better.
 * Considering the name of the article Pound-foot (torque), it is more intuitive that force comes first and distance follows in the combined unit. The article torque also refers to lbf·ft and N·m, where again force comes first and distance follows, and it also states "This avoids ambiguity with mN, millinewtons.". So, repeating for the third time, ft·lb or ft·lbf is not necessarily wrong, which is also stated in the article Pound-foot (torque); "foot-pound (ft·lb or ft·lbf) is also sometimes used interchangeably with "pound-foot" to express torque". The thing is, consistency is an important aspect of scientific writing, and the version you insist on reverting to is "This was rounded to an even 33,000 ft·lbf/min. Watt calculated the power as 33,000 ft-lb per minute.", where two different notations of the same unit "ft·lbf/min" and "ft-lb per minute" are written side by side.
 * I find it great that people from all over the world are the editors of this place, but you seem to have a problem in reading comprehension of English language and/or you seem to have a tendency to revert edits without understanding them. In either case, please refrain yourself from reverting the edits made to English \\//ikipedia by other editors, especially when they are reasoned well enough in the talk page of the article and you find it difficult to understand the text and/or want to revert it for no valid reason. None of us have so much time in our hands and this was far too long, far too inefficient. Note that these kind of actions frustrate editors and thus prohibit improvements in \\//ikipedia. I might also suggest that you'd better refrain yourself from editing the articles in English \\//ikipedia before taking others' opinions that your language is coherent and consistent enough, which would not be ambiguous for readers.


 * 85.110.88.64 (talk) 16:12, 6 December 2014 (UTC)
 * Wikipedia has a policy of no personal attacks.  In your last post you made a personal attack on me.  Cut it out!


 * Relax, nobody made a personal attack on you, you misinterpret what you read because, as your profile says, you don't understand English. just refrain yourself from editing articles or other editor's edits in English \\//ikipedia until you get a better grasp of English, because it takes too much time to explain to you what the edits actually tell. Posting the "welcome to wikipedia" message in the talk page, and then the warning message against getting banned due to edit war was quite strange though I must say. There is no point in playing witty games. Many edits to \\//ikipedia are made in good faith. Although you insisted on reverting the tiny edit I made again and again without understanding it at all, the edit is still there. There was nothing to revert once you could understand it, because it fixed what was wrong about the article. It just took you so long to understand. This is a fact, not an attack. 85.110.88.64 (talk) 22:26, 6 December 2014 (UTC)


 * Torque is not relevant here. I realise that torque is measured in foot-pounds.  I did not know (before this conversation) that some books express this a pound-feet.  One of the good things about Wikipedia is that you learn new things every day.  I can see that there are advantages in expressing torque as pound-feet, because that makes it clearer than the measure is of torque and not energy (energy is also measured in foot-pounds).


 * Yes, torque is quite relevant here, in fact I already explained what its relevance was more than once. Just keep reading the contents of this section again and again, it'll sink in. Hint: Power is also torque times angular speed, and it isn't surprising at all that there is a (mechanical) power calculation in the torque article, so perhaps a good candidate for your favorite English word can be "consistency". Anyway, I'm glad you learned something with this discussion, because honestly I was so sure it turned out to be completely useless. 85.110.88.64 (talk) 22:26, 6 December 2014 (UTC)


 * In the version before your edit, citation 12 was "Coon, Brett A. Handley, David M. Marshall, Craig (2012). Principles of engineering. Clifton Park, N.Y.: Delmar Cengage Learning. p. 202. ISBN 978-1-435-42836-2." Page 202 does not have the quotation ("Two horses together produced over thirty hp") you claim it does.--  Toddy1 (talk) 17:57, 6 December 2014 (UTC)


 * In this beginning of this section, my first post gives all the details of the reference I removed. Just read, it'll sink in. Very easy, just go to the beginning of this section, and read my first post slowly. Believe it or not, it'll tell you everything you want to know. 85.110.88.64 (talk) 22:26, 6 December 2014 (UTC)

Confusing Formulae
Why do the equations for drawbar pull use expressions like v/mph instead of just 'v'? it makes the equations look much more complicated than they really are and I've not seen equations written like this before. Can someone who is good with an equation editor tidy them up? Stub Mandrel (talk) 18:11, 23 February 2015 (UTC)


 * Apparently, this way of describing mathematical relations is referred to as quantity calculus. Since I’ve just found quite a nice book (published by The Royal Society of Chemistry), I can recommend it to you as well: The 2nd and 3rdeditions have been made available online as PDF files.[1] I can provide below excerpts:


 * Quantity calculus is a system of algebra in which symbols are consistently used to represent physical quantities and not their numerical values expressed in certain units. Thus we always take the values of physical quantities to be the product of a numerical value and a unit, and we manipulate the symbols for physical quantities, numerical values, and units by the ordinary rules of algebra. This system is recommended for general use in science and technology. Quantity calculus has particular advantages in facilitating the problems of converting between different units and different systems of units.
 * A more appropriate name for "quantity calculus" might be "algebra of quantities", because the principles of algebra rather than calculus (in the sense of differential and integral calculus) are involved.
 * - Quantities, Units and Symbols in Physical Chemistry, 2007, p. 131
 * - Quantities, Units and Symbols in Physical Chemistry, 2007, p. 131


 * If it is desired to write the relationship between numerical values it should be written in the form:
 * $A/(S\ mol^{-1}\ cm^2)= \frac{1000\ K/(S\ cm^{-1})}{c/(mol\ dm^{-3})}$
 * - Quantities, Units and Symbols in Physical Chemistry, 2007, p. 132


 * Quantity equations: Equations between quantities are used in preference to equations between numerical values, and symbols representing numerical values are different from symbols representing the corresponding quantities. When a numerical-value equation is used, it is properly written and the corresponding quantity equation is given where possible."
 * proper: (l/m) = 3.6-1 [v/(km/h)](t/s)
 * improper: l = 3.6-1 vt, accompanied by text saying, "where l is in meters, v is in kilometers per hour, and t is in seconds
 * - The NIST Reference on Constants, Units, and Uncertainty / SI Unit rules and style conventions / Quantity equations


 * I agree that equations look more complicated than they really are in this form.
 * WaveWhirler (talk) 22:27, 27 February 2015 (UTC)

RHP?
In TSS Maianbar, RHP is a piped link pointing here. I assume it's "rated horsepower" but I'm not clear whether that's different from saying it's rated at x horsepower.

In any case the lack of reference to RHP in the horsepower article will be confusing for someone following that link. --Chriswaterguy talk 23:58, 22 April 2015 (UTC)


 * Rated horsepower (rhp) is the nominal horsepower (nhp) of the engine. TSS Maianbar is updated.
 * 85.110.3.22 (talk) 07:53, 27 April 2015 (UTC)

800 watts /hp
I am puzzled why early on in the article, the third sentence states "The most common horsepower—especially for electrical power—is 1 hp = 800 watts." I believe that should read "The most common horsepower—especially for electrical power—is 1 hp = 746 watts." Of the 5 definitions listed in the definition section, none would round to 800. Three of the 5 definitions would round to 746 or 750 or 700, one to 736 or 740 or 700, and none round correctly to 800. Three quarters of a kilowatt is a very useful and pretty accurate approximation, ~0.5% error. I've rarely if ever encountered using 4/5 of a kw (800 watts) as the approximation, in about 4 decades of engineering practice. — Preceding unsigned comment added by 144.92.224.3 (talk) 16:40, 2 July 2015 (UTC)

rounding correction
Slight correction on rounding; rounding to 735 in one definition, not to 736, since value indicated is ever so slightly below 735.5, the round-to-even does not come into play. — Preceding unsigned comment added by 144.92.224.3 (talk) 16:45, 2 July 2015 (UTC)

"Break" horsepower
BHP stands for "break horsepower"? What does the "brake" in "brake horsepower" mean? Should be covered in the article IMHO.--Polis Tyrol (talk) 08:24, 5 January 2016 (UTC)

Equals equals equals
What the hell are all the "equals" supposed to mean in the "Measurement" section? — Preceding unsigned comment added by 124.150.172.94 (talk) 13:03, 12 June 2016 (UTC)

Original horse power
The original horsepower unit was selected to show potential buyers of the new steam engines how much they would save by switching from horses to steam. The horsepower unit represented the rate of work a horse could do on a continous basis (all day long). Thats why its only a small fraction of the maximum capability of a horse. — Preceding unsigned comment added by Motorhead (talk • contribs) 17:38, 3 April 2005 (UTC)

Why is this entry flagged?
"This article or section may contain original research or unverified claims." How so? — Preceding unsigned comment added by 60.50.43.38 (talk) 05:58, 3 October 2008 (UTC)

Khalid Ahmed jabir
kalid — Preceding unsigned comment added by 213.55.105.85 (talk) 06:14, 11 October 2016 (UTC)

eshp
might somebody please deign to explain what the designation "eshp" - very much in use to quantify the power of aircraft engines - means, contentwise and letter by letter? the article "Kuznetsov NK-12" e.g. links here, but I for one can't find the combination of letters... thanx! --HilmarHansWerner (talk) 05:57, 2 January 2016 (UTC)
 * equivalent shaft horse power
 * It allows for the effect of jet thrust from the engine additional to the shaft power delivered to the propeller 86.148.153.168 (talk) 12:08, 26 November 2016 (UTC)

I found a reference and added a paragraph for this. Kendall-K1 (talk) 15:07, 17 January 2018 (UTC)

ISO section
Could you explain why you think it's a problem that the descriptions of the ISO specs are sourced to the specs themselves? Do you doubt that the specs describe themselves correctly? Do you think this information is not important enough to include? Something else? Kendall-K1 (talk) 06:39, 18 January 2018 (UTC)
 * The ISO documents are primary sources. Secondary or tertiary sources are needed to establish their notability and to provide an interpretation of them. If secondary sources cannot be found, this shows that the ISO documents are non-notable.


 * The documents themselves are published by an organisation that functions as a business. It sells products/services.  An analogy might be a new version of Persil washing powder.  It would be very unsatisfactory if the only source was what was printed on the side of packets of new-Persil.--  Toddy1 (talk) 20:21, 18 January 2018 (UTC)
 * There is nothing wrong with citing primary sources to verify what those primary sources say. In fact, our policy says explicitly: "A primary source may only be used on Wikipedia to make straightforward, descriptive statements of facts that can be verified by any educated person with access to the primary source...." That's what is being done here. This isn't a notability issue. Our notability guidelines don't apply to sections of an article about an unarguably notable subject. ~Anachronist (talk) 22:01, 18 January 2018 (UTC)
 * "Secondary or tertiary sources are needed to establish their notability" is a classic misreading of the notability guidelines. That's why WP:NNC is given such a prominent place at the top of the Notability page. As Anachronist says, the policy on primary sources only says they, should not be the sole basis for creating a standalone article, echoing the notability policy. But this isn't a standalone article, so all that is irrelevant. We should be basing this on content policy (which are quite inclusive and open to whatever consensus comes up with), not notability.It is relevant to say that we shouldn't analyze or interpret the meaning of primary sources with no further citations. But the section in question doesn't contain any analysis or interpretation. It's merely a list of ISO standards and their topics. And that raises what might be the most relevant policy: WP:NOTCATALOG. Why do we have a section with no information other than a list of DIN, JIS, ISO and so forth standard titles or index numbers? I can attest that there is an encyclopedic need to explain the differences between SAE Net, SAE Gross, DIN, etc type of horsepower. Readers are given these statistics in many contexts and they need to understand what they mean. Wikipedia has many thousands of articles that give this data and this is the article we send those readers to when they need clarification on what we mean by DIN or SAE Certified power. So can the same be said of ISO 14396 or ISO 1585? Where are readers seeing these standards that might make them want clarification? Are there meaningful differences between them that we can explain? Perhaps we should rewrite this content so we're telling readers whether or not DIN 70020 or ISO 1585 or SAE net power are similar or not quite the same. To me that is the most relevant question. You have these standards thrown around and many are synonyms and many are critically different. Regardless of which approach we take, we should try to get away from primary sources and rely on secondary sources for this. I would be that a secondary source discussing the ISO standards will indeed look much more encyclopedic.  --Dennis Bratland (talk) 22:22, 18 January 2018 (UTC)

Compressed air horsepower
I have deleted this entire section as patent nonsense. It is not horsepower (power) that is consumed compressing a stated volume of air to a stated pressure. It is energy that is consumed. A given volume of air can be compressed to the same pressure using one tenth of the amount of power - it just takes ten times as long to do it (i.e. the same energy). In practice it would probably take longer because of loses in the compressor and possible leakage. TheVicarsCat (talk) 12:52, 13 April 2018 (UTC)

Indicated horsepower, convert and unit conversions?
There are a couple of problems with : 5,600 ihp

Firstly it links to a section within Horsepower; if it used a redirect instead this would be more robust. Secondly it gives a conversion to kW. Is this really credible as a conversion? This isn't a nominal or tax horsepower, where it would be simply wrong, but it is also quite inaccurate, as indicated horsepower ignores a number of major losses that would have to be included for any way to measure kW, such as by brake horsepower.

Should this conversion be supported? Or is indicated horsepower simply a stand-alone measure? Andy Dingley (talk) 23:18, 19 April 2016 (UTC)


 * The unit is horse power, which has several context-specific forms, e.g. electric/water/boiler horse power as well as several measurement-specific forms, e.g. indicated/nominal/break horse power, all of which express the measured quantity in terms of the very same unit (i.e. horse power) despite consisting of different symbols in the unit's abbreviation, which reflect different contexts and/or different principles of measurement.


 * The additional factors (e.g. friction, vibration, etc.) that are neglected/accounted-for in the definition of a particular context/measurement-specific form of a unit will most definitely be different for different products, and they may not be the same even for two samples of the same product that came out of the same production line (and will almost definitely vary with time). Therefore a context/measurement-specific form of a unit, in any system of measurement, is _not_ subject to conversion.


 * My suggestion would be that the default behaviour of the conversion template for context/measurement-specific forms of units should be double-output indicating the essential equivalence to the underlying unit (hp in this case) and the corresponding SI counterpart, e.g. : 5,600 ihp. Removing the support for the conversion entirely is also an option as you questioned, but then again inclusionism seems to be fashionable in Wikipedia. Frankly, I don't think anybody would look for a generic conversion for a context/measurement-specific form of a unit, therefore its presence would not be a bigger problem than its absence, I think.


 * WaveWhirler (talk) 20:10, 23 April 2016 (UTC)
 * I've been accused of being an inclusionist before, but I think we should only include things when their advantages outweigh their disadvantages.
 * There's no point in a numerically precise conversion from ihp to W as this is just never going to be accurate. An approximate conversion is something a reader already familiar with the meaning of ihp is going to do in their head. Offering a conversion to a naive reader is to mislead them: it implies that 1 ihp = 746W, when it's some sizable factor less than this. Andy Dingley (talk) 22:00, 23 April 2016 (UTC)
 * The convert function rounds too generously but doesn't indicate this. 33 000 ft⋅lbf is not 45 000 Nm as written, it is 44 742 Nm. 45 000 Nm is OK but only if indicated as a derived rounded figure.Theosch (talk) 11:24, 27 September 2018 (UTC)
 * When you tell the template to convert 33,000 it has no way of knowing how much precision you want. It guesses that you want two significant figures, which is a reasonable assumption in most cases. But in this case 33,000 is a precise definition, so the template must be told that you want five (or more) figures. I have fixed this in one place in the article. This is really a separate problem from ihp conversion. Kendall-K1 (talk) 12:17, 27 September 2018 (UTC)


 * ferraresi 2019-04-16

In accordance with IEC 60034-1, item 5.5.3, the conversion of power units shall be as follows. 1 hp = 0,7457 kW 1 cv = 0,736 kW — Preceding unsigned comment added by Ferraresi (talk • contribs) 11:19, 16 April 2019 (UTC)

Accuracy
Is there such a thing as an accurate measure of horsepower (or power output). This article seems to think there is. I thought the measurement depended on so many factors (I'm no engineer but air pressure comes to mind) that in practice it is impossible to be exact. Regards to all. Eddaido (talk) 09:17, 14 December 2020 (UTC)


 * I would think you can measure it accurately ok.  And indeed there are various different approaches to doing so.   But (despite being, like you, no engineer) I would agree that if you measure bhp (or whatever your preferred version of horse power may be) of the same car on seven different occasions, possibly on seven different days, you will indeed get seven different measurements.   With any luck, they'll all be quite close, but features such as the ambitent temperature, humidity and air pressure would presumably come into the equation because they would affect the composition and character of the gas drawn into the combustion chamber.  Fuel quality too.   Other factors would presumably include the temperature of the engine, the state of the carb(s) and/or the decision processes of the computer controlled injection, it's oil, it's coolant, the condition of the seals / piston rings / valves and - if you measure the power output with the engine still installed in the car - various equivalent considerations involving back-pressure (i.e what you have stuffed in your muffler / silencer boxes front and back/ exhaust system) and the gear box.   But if there is a real live engineer with appropriate expertise among us, his (or her?)  answer might be more helpful than this one.


 * I think you may have been involved with auditors at some point.  Do you not remember the suspicion triggered when the answer to any question was 10, 100, 1,000 or 1,000,000?   If numbers are that round / approximate - and in the anglosphere we have an ongoing preferences for "round numbers" - they are most likely seriously inaccurate.   Then think back to the 1930s, 1940s, 1950s, 1960s and recall how many cars were advertised as delivering 100 horsepower.    Not 98 or 106 but 100.   But you get to the point - and the marketing department agrees with you - where it becomes important to provide a value.   And .... hmmmm. Be well.  Charles01 (talk) 09:46, 14 December 2020 (UTC)


 * I'm a software engineer rather than a mechanical engineer but I'm car mad and have worked professionally on car/truck ECUs (including assisting on dyno testing).
 * Any measurement will have repeatability issues. This goes from measuring my height (which is affected by the moon's pull, whether I'm stooping, hair style, the size of my lunch, etc) to measuring the distance to the moon (it's position in it's orbit, measuring to a Luna mountain or plain, measuring from an Earth mountain or plain, atmospheric conditions, etc). The trick is to list all the conditions and try to do the next measurement under the same conditions. This is often not possible (eg one magazine measures hp, a second magazine also measures it but doesn't know most of those conditions). So we just take a stab and hope that the various measurements are close. Gets tricky when one measurement is done at sea level near the coast in winter (cool, dense air has more oxygen) and another is done near a desert in summer (hot air has less oxygen). In lab conditions, they measure air density, temperature, etc and then apply adjustment factors. Dyno runs at your local speed shop also do this. Dyno numbers can be greatly exaggerated by telling the dyno that the air temp is really hot A. good dyno report will list air conditions and whether the graph is raw numbers or adjusted numbers but not all dyno reports list these. To summarise, hp is a well defined unit but the practice of measuring it takes great skill that is not always used.  Stepho  talk 00:38, 15 December 2020 (UTC)
 * This video might interest some of you on horsepower. https://www.youtube.com/watch?v=gC2-JKO0c2I&feature=youtu.be Avi8tor (talk) 11:24, 15 December 2020 (UTC)

Can RAC horsepower be converted?
I don't belong here but I thought this might interest somebody. Can RAC horsepower ([https://en.wikipedia.org/wiki/Horsepower#RAC_horsepower_(taxable_horsepower. here], here, and [https://www.designchambers.com/wolfhound/wolfhoundRACHP.htm. here]) be converted into a scientific measurement?

RAC horsepower (AKA "Taxable" and "A.M.A." in the US) is figured on a formula, one with obvious problems. It does not measure anything except the bore and the number of cylinders. I believe that this: "$$\text{RAC h.p.} = \frac{D \times D \times n}{2.5}$$ where D is the diameter (or bore) of the cylinder in inches, and n is the number of cylinders" is the equation, I take this as Bore X Bore X Number of cylinders divided by 2.5. (Please forgive my poor math). The exact formula doesn't really matter, though, just that it is a formula.

Bore X bore doesn't mean anything to a circle, there is no 3.14. And there is no provision for stroke. Or any other variable than the number of cylinders. There is no physical measurement of displacement, engine speed, even the type of engine, flathead vs. OHC (example). You set the horsepower on the first blank page, nothing else affects it. It only measures a piece of paper, and in a strange way, too.

Horsepower is measured many ways, I think most actually measure some physical force. RAC horsepower does not. There was a plan to get to the formula, but the formula itself is both useless and a formula, not a physical measure.

Can a formula (especially a stupid one) be converted into a scientifically measured unit? It has been discussed a little [https://en.wikipedia.org/wiki/Talk:Rover_Company#Horsepower. here] and on editor's talk pages. Thank you. Sammy D III (talk) 10:14, 15 December 2020 (UTC)


 * The RAC fiscal horsepower was only invented in 1910 and only for automobiles apparently. https://automobile.fandom.com/wiki/Tax_horsepower Avi8tor (talk) 11:30, 15 December 2020 (UTC)
 * Agreed, although your source is circular. Note to others: we have also been talking about what measurement was used where. Here I said "The exact formula doesn't really matter, though, just that it is a formula.".
 * I don't quite understand you using "fiscal". "Tax" is common, even if "fiscal" is accurate. Accent? Sammy D III (talk) 11:53, 15 December 2020 (UTC)
 * Just another English word. No accent. Avi8tor (talk) 17:41, 16 December 2020 (UTC)


 * This is one of those "gotchas" that inevitably comes up when you're investigating really old automobiles from the early 1900s or earlier. The RAC formula (or its equivalents, like the NACC and ALAM formulas) is simply not a reliable horsepower figure, but despite this it was used commonly enough in the period that before you can trust a claimed horsepower figure, you first need to verify that it is *not* computed from the RAC formula but is a genuine rating such as might be measured with a dynamometer. Unfortunately many people in this period were ignorant enough about how engine power worked to blindly trust and repeat RAC figures. The RAC formula was derived by making a whole bunch of assumptions about how gasoline automobile engines would behave, such as their maximum piston speeds, compression ratio, and so forth, which is why so many factors are not considered in the formula. When the formula was first drafted, those assumptions were frequently correct, but they very quickly became out of date, so RAC figures are usually severe underestimates.


 * Interestingly, a similar "gotcha" comes up with steam engines during the 1800s, especially in applications such as steamships. In this case the old, outdated formula with too many assumptions is known as "nominal horsepower", or n.h.p., while the actual power generation figures would be indicated horsepower (i.h.p.) or shaft horsepower (s.h.p.). --Colin Douglas Howell (talk) 19:28, 16 December 2020 (UTC)

U.S. states taxes and "RAC" horsepower
Please note this description of the 1926 "The Franklin Sedan" The SAE formula used is the RAC formula. This is 1926 - almost within living memory ! !
 * Engine  - Six cylinder, vertical, cast en block, 3-1/4 x 4 inches; head removable; valves in head; H.P. 25.3, S.A.E. formula

When did the last state end using this as a basis for taxing automobile owners? Eddaido (talk) 13:04, 15 December 2020 (UTC)
 * A 1969 MG (BGT) Coupe had 15.9 horsepower in 1976 in Illinois. What was yours? Sammy D III (talk) 13:17, 15 December 2020 (UTC)
 * Good Heavens! To answer your question, engine size so far as I know has never been a factor in the calculation. I think it is entirely related to the use of the vehicle. Light trucks are regarded as something like cars but heavy vehicles are subject to all sorts of complicated calculations, I think. Maybe some part of it is the expected damage to the road and maybe they take into account mileage from locked hub meters. Do you really want me to try to find out? Past bed time, Eddaido (talk) 13:34, 15 December 2020 (UTC)
 * No thanks. An XJ had 33.5 in 1995, new form w/o hp in 1996. I doubt anyone can be more backwards, we may have finally put it out of its misery. Sammy D III (talk) 13:45, 15 December 2020 (UTC)
 * I have been told that ALAM and NACC hp are equal to RAC hp; at Tax horsepower it is stated that Missouri still uses it to calculate fees and whatnots! Amazing.  Mr.choppers &#124;   ✎  18:25, 16 December 2020 (UTC)
 * Circa 2005 I upgraded my Celica from a SOHC 88 hp 18R-C to a twincam DOHC 140 hp 18R-G. Same block, just different compression ratio, head and cams. The government form said "Does the new engine have the same RAC rated horsepower?" Since they had the same bore I could happily tick that box. That was Western Australia, 2005.  Stepho  talk 21:33, 16 December 2020 (UTC)
 * I think in the 1960s Illinois had an under/over deal that broke generally as I6/V8, that would make sense here. When things opened up in the 1970s that probably wouldn't work, though, the number may have been vestigial for years. I can't remember ever caring. It's one size fits all now, why should a 3/4-ton Cadillac "SUV" carryall pay more than Chevy's cheapest he says bitterly. Missouri isn't known to be progressive, but that's really impressive.
 * Trucks do it right here, they drive on a scale first and then get the calculator.
 * Stepho, "just"? Sammy D III (talk) 22:54, 16 December 2020 (UTC)
 * Yep, in the eyes of the Department of Transport, it was "just" swapping to another variant of the same engine (same family, same bore, same capacity). But it gave tyre frying fun for me :)  Stepho  talk 14:32, 17 December 2020 (UTC)

Nhp table needs column headings
The nhp table is pretty useless as-is. The first column is ship's name. That only takes a second to figure out, by noticing the italics and clicking on one. My guess is that the second and third columns are ihp and nhp, but I don't know which is which. The fourth is apparently the ratio of the two, but without knowing the others it's useless too. Can someone add column headings? Also per WP:DONTHIDE the table should be uncollapsed by default. GA-RT-22 (talk) 17:40, 28 March 2021 (UTC)


 * ✅  Stepho  talk 09:31, 3 April 2021 (UTC)