Talk:Horsepower

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?

-- Chris Q 12:32 Sep 17, 2002 (UTC)

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

Contents

1 Now 2 Real power of the horse? 3 Original horse power 4 Derivation for HP Equation 5 Pound mass 6 Determining horsepower 7 Horse-power machine 8 Morven's comments from User talk:Bobblewik 9 Coping with ambiguity in the term 'horsepower' 10 ambiguity in PS

Now

The article dosen't explain how horsepower is measured today. [This text was submitted unsigned by ]

Do you mean the machinery involved, or the way it is calculated? Most of this is not actually done in horsepower anymore, what with the worldwide adoption of the metric system; thus it is better discussed at a system-independent place. —Morven 06:14, Jul 9, 2004 (UTC)

Real power of the horse?

I read somewhere that HP is defined smaller than real power of the horse is, in order to make better marketing effect for first engines. Can someone confirm this, plz? saigon_from_europe

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.

Derivation for HP Equation

Could someone possibly go through the derivation for equating Horsepower to RPM and Torque of an engine or motor. I know that <math>\mathbf{HP} = {\mathbf{Torque} * \mathbf{RPM} \over 5252}<math> is the equation, I just seem to be at a loss as to show the derivation as my algebra skills aren't exactly top notch. Jason Gillman Jr.

First of all, that won't give you the relationship between typical horsepower ratings and typical torque ratings, because each is usually expressed at a different RPM, and neither of the associated curves are linear functions of the rotational speed.

What units are you using for torque? That's part of it. For the particular numbers you have, you need to use lbf·ft (or ft·lbf if you prefer).

Express horsepower in terms of feet, pounds-force, and some time unit. The article does that for you.

A revolution is 2×&pi radians. Convert revolutions per minute to radians per minute or per second, whchever time unit you used with the horsepower. Radians are actually dimensionless. Ignore them in your final units.

Multiply 5252 by π and round to 4 significant digits, since that's all you have in that 5252 number. Then double it (or, you could just multiply by 2π in the first place). Is the familiar number a helpful hint? Gene Nygaard 01:11, 6 Apr 2005 (UTC)

I wrote this up at torque. Samw 03:20, 9 Apr 2005 (UTC)

Pound mass

The article said "15,000 pound mass" - this is clearly wrong.This number is repeated in the SI approximation. I'll change this. I always thought that the "pound-foot" system unit of mass is the slug (pounds weight divided by G). Wikipedia says there's a pound mass and a pound force but I'm confused...I thought a pound was defined as the *weight* of the mass, not the mass? --Wtshymanski 03:42, 7 Apr 2005 (UTC)

Like you said, you are confused. THe unfortunate thing is that there are far too many teachers in the same boat. Maybe a look at poundal and pound-force will help you out. Of course, you could actually lookup the definition of a pound, too—here's the official U.S. definition, and as it points out, the official definition in the rest of the world as well.[1] (http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf)

It is, in fact, the pound-force which is the recent bastardization, a unit never well-defined before the 20th century, and one which even today doesn't have an official definition. -- Gene Nygaard 04:43, 7 Apr 2005 (UTC)

I forgot to mention that you were not so confused as to not catch that 15,000 pound error. Good job on that. Gene Nygaard 04:45, 7 Apr 2005 (UTC)

Luckily, I never have to worry about pounds (forece) and pounds (mass)- I understand kilograms and newtons adequately. But I knew the "15,000" didn't fit! --Wtshymanski 03:25, 8 Apr 2005 (UTC)

Determining horsepower

Is there a simple method that a common layman could use to determine approximate horsepower of a car's engine?? Jaberwocky6669 18:37, May 3, 2005 (UTC)

Unfortunately, no. A quick look at many engines will show you that engine size is not necessarily all that indicative of horsepower (all else being equal, of course, it often will be, but all else isn't equal) —Morven 19:45, May 3, 2005 (UTC)

Sure there is: take the kilowatt value, multiply by four and divide by three. Christoph Päper 13:49, 4 May 2005 (UTC)

Horse-power machine

A horse-power is also a device used to power some other machine, where a horse or several horses were walked in a circle or on a belt to provide power. An example in a historical text is here: http://bchs.kearney.net/BTales_199303.html

Unless I miss my guess, it is the name of this machine from which the horsepower unit took its name, since this is what steam engines were devised to replace.

There were many machines that were operated by horses. The cited URL uses "horse power" as the adjective for how the machine is operated and not for the machine itself. I'm not aware of any machine named "horse power". But yes, clearly "horsepower" comes from the way machines were powered with horses. Samw 03:26, 24 May 2005 (UTC)

It is my impression that there were modular "horse power" machines that could be used to power many other machines, such as threshers, water pumps, etc., much as early belt-drive stationary steam engines could be attached to different machines to power them. I have seen a horse power machine on display at the Pioneer Auto exhibit in Murdo, South Dakota.

Interesting. I guess it makes sense to re-use portions of the machine that are on the "horse-end": the harnesses, the main rotor, etc. If you have references, it would make an interesting historical footnote on alternate historical uses of the word "horsepower". Samw 03:26, 29 May 2005 (UTC)

Morven's comments from User talk:Bobblewik

Horsepower is a complicated issue. Part of it is to do with there being two definitions of horsepower: Imperial horsepower (1 hp = 33,000 ft·lbf·min^-1) and German pferdstarke (nowadays defined in terms of SI units: 1 PS = 75 kp·m/s = 735.49875 W). The two thus differ slightly; by my calculations, 1 hp = 1.014 PS.

Fairly often, in non US markets, a power rating is given in 'hp' in English-language publication, but the values are actually 'PS' unconverted. This is even sometimes true for British or American products sold on the world market.

In the US market for automobiles, true hp is used.

The second problem is how the power is measured. In the modern day, power measurements are in SAE net horsepower in the US, and DIN net (kW|horsepower) or JIS net (kW|horsepower) in most other markets. The testing method for both is the same; horsepower is measured at the engine flywheel with all engine accessories attached, alternator fully loaded, emissions-control equipment installed, and the production exhaust system attached. Thus, the difference between SAE and DIN/JIS ratings is largely explainable by the hp/PS difference above.

Before 1972, US manufacturers used SAE gross horsepower. This tested the engine's power at the flywheel without most accessories attached, no pollution control equipment, and an open, unrestricted exhaust system. This gave power figures approx 20% higher than SAE net, although there is much variation. Thus power figures for 1972 and later US cars cannot be directly compared with those quoted for earlier vehicles. A failure to understand this change exacerbated the impression left on the US consumer that emissions and fuel-economy laws in the 1970s ruined US cars. There was, indeed, much of a reduction in power, but the change in measurement method exaggerated it.

Added to all this, of course, is the fact that horsepower figures in the press are advertising numbers rather than engineering numbers, and thus are often rounded roughly, exaggerated or even minimised. It has in fact been quite common for mass-market manufacturers to understate the power of their high-performance vehicles, perhaps to avoid bad publicity or high insurance charges for the new owners. This affects figures in both kW and hp.

I would suggest that when we quote horsepower figures in car articles, we should state which hp is being talked about. For US-market automobiles in the modern day, we should state hp (SAE net) or SAE net horsepower, I think. It is safe to perform conversions to kW using the standard ratio, since SAE hp is measured in the same manner as DIN kW. Older US-market automobiles should be quoted as hp (SAE gross). We should also flag kW conversions for those vehicles as (gross) as a warning that they are not directly comparable to DIN kW figures.

In general, we should obtain the original kW figures for vehicles sold outside the US, since in most modern cases this will be the original measurement and the hp a conversion. We should also flag hp conversions as to whether they are DIN or JIS net hp (which are generally actually PS) or SAE net.

I am not sure which figures are generally used in the UK market; the figures are normally quoted in 'brake horsepower' (bhp), but what this exactly means, I'm unsure. I suspect it is probably quite equivalent to SAE net, but more research is probably needed here.

I hope this complicated explanation helps more than it hinders! —Morven 13:34, May 26, 2005 (UTC)

---

I copied the above from User talk:Bobblewik to make sure the information don't get lost. Some of it is here already, but much isn't. Unfortunately it is not a topic I know well enough to integrate it in. -- ALoan (Talk) 12:26, 27 May 2005 (UTC)

On the basis of all the help from everybody, I have been correcting the errors in Mercedes-Benz articles. I note that Morven said:

a power rating is given in 'hp' in English-language publication, but the values are actually 'PS' unconverted. This is even sometimes true for British or American products sold on the world market

I see now that it can even be inconsistent for the same product, language and region. For example, Mercedes Benz USA quotes the 150 kW engine as having 201 hp (presumably SAE net) in one part of the site and as having 204 hp (presumably DIN) in another part of the site. Sigh. Bobblewik  (talk) 18:39, 28 May 2005 (UTC)

There you are, going off half-cocked again, Bobblewik. Please do not go around changing these numbers to "hp (DIN)". Using the symbol "hp" for the metric horsepower is unacceptable; spell out metric horsepower or one of its other names, or use a symbol which is acceptable. The symbol PS is not only the German symbol for this unit, but also the one most often used in English, though other symbols such as CV are occasionally seen. Then, if you are indeed sure that this is the original measurement, please list the original measurement first, followed by the conversion to kilowatts. If you don't think it is the original measurement, don't list it; list "hp" (English horsepower) instead. And please, go back and fix the articles you have messed up now. Gene Nygaard 19:00, May 28, 2005 (UTC)

I would strongly recommend against ever using "CV" to mean anything except French tax horsepower, unrelated to real power ratings. The general English-language exposure to the term is purely for that purpose.

For European and Japanese vehicles, I would suggest never using an offically listed "hp" rating unless we are absolutely sure that it was the original measurement. In almost all these cases, the original measurement would be the kW or MW one. We should then provide a hp conversion in terms of Imperial/US customary horsepower, using the standard conversion ratio. Except in cases where we are sure that the original design / measurement was in PS ("metric horsepower"), we should not use that unit in Wikipedia. All it adds is confusion to the reader.

For US-market cars, we should differentiate between SAE gross and SAE net horsepower. At the very least, all ratings in gross horsepower should be marked as such, to indicate that they cannot be compared with modern power ratings (net power being the accepted modern standard worldwide). —Morven 07:21, May 29, 2005 (UTC)

Gene Nygaard has told me that he is unhappy with my contributions. So I am asking for others to try to help fix the articles. I raised this issue of unreliable horsepower values and have added kilowatt values that my research makes me believe are accurate. In the absence of guidance, I changed the ambiguous term 'hp' to the term 'hp DIN'. If I should have changed 'hp' to 'PS' or 'CV', then mea culpa (my mistake). I have my flaws as do we all, but I have acted in good faith. I don't like being the target of expressions like 'half-cocked' and 'screwups'. Gene, we are both champions of good use of units, I respect your knowledge and dedication to research about units. Please treat me as your friend or at least collaborator, I am certainly not your enemy.

I ask Gene and others to examine the edits that I have made to car articles and try to improve them. I also ask for community guidance on terminology. I am prepared to put in some effort to fix the problems caused by the use of 'hp' as a primary value. I welcome positive actions and positive thoughts in support of this. Bobblewik  (talk) 12:19, 29 May 2005 (UTC)

Sorry to be so abrupt about it, just commenting on your habits of rushing off to do a huge number of changes before being sure that you've gotten it right. Did you even notice that User:Morven used "PS" to distinguish from "hp"? I'm glad to see that you are willing to put in some effort into tracking down the changes you've already made; from what I've seen before, that's something you rarely do, which is why I made sure to categorize your changes this time as a "screw-up".

The fact of the matter is that most of these measurements (probably even for current production) were made in either English horsepower or metric horsepower, with the kilowatts figure being a conversion, and almost all for the majority of the articles which include measurements made at some time in the past. I urge you and all contributors to be aware of this problem, and if the source of your information lists numbers in both horsepower and kilowatts, be sure to check to see which horsepower was used there before putting it into the article, and disambiguate them here even if your source didn't do so. As I've said before, I think the best way to do that is to use "PS" (linked to horsepower on first use) as the symbol for metric horsepower, though if some other method is already used, I wouldn't bother changing it unless it uses "hp" (even with your parenthetical DIN this seems unclear). It's not only that "hp (DIN)" has never been explained in this "horsepower" article itself, but in fact the "DIN" is never mentioned at all in the article itself, and you did not provide either a spelled out version of DIN or a link to its article DIN either. Gene Nygaard 12:44, May 29, 2005 (UTC)

After some research I have discovered the there is a European Directive on this: 80/1269/EEC (and modified by: 88/195/EEC, 89/491/EEC, 97/21/EC and 1999/99/EC).

This Directive harmonises national legislation on the method of measuring engine power that must be used to indicate the engine power of a vehicle type.

Henceforth, no Member State may refuse to grant EEC type approval or national type approval in respect of a vehicle, or refuse or prohibit the sale, registration, entry into service or use of a vehicle on grounds relating to its engine power, if this has been determined in accordance with the Annexes to the Directive.

So perhaps the method of measurement itself has been harmonised in Europe, or will harmonise. I hope that somebody can make something of that. Bobblewik  (talk) 01:14, 30 May 2005 (UTC)

So let's cut this down to the convention for Wikipedia. We already discussed the issue at Wikipedia:WikiProject Automobiles/Conventions and decided to use hp (presumably SAE net or gross depending on time period) or kW depending on market for this unit. I am opposed to using PS or metric horsepower - it's just plain confusing. One exception is if the metric hp number is "significant" - as in the Bugatti Veyron with it's 1001 hp (metric) engine. I will propose an ammendment over there to always specify "hp SAE" rather than just "hp" and see what people think. Or we could just link the first occurrence of "hp" to horsepower#hp (SAE) and let people use their intiution that all remaining references to hp are for SAE numbers. I like this better. We DO have to be precise, and I don't want to go around using random units everywhere.

So let's decide here and now:

• I propose never using metric horsepower as a primary unit unless it's a special case like the Bugatti. And then we should be very specific in including the SAE number.
• We've already decided to always include both hp and kW, and that's all well and good.
• As for notation, if we are to specify SAE, I would do it without parentheses since we are using the parens for kW already. So we say "100 hp SAE (74 kW)". I'd rather not include the SAE at all, but this is a reasonable alternative.

--SFoskett 14:39, May 31, 2005 (UTC)

As I've said in Wikipedia Talk:WikiProject Automobiles/Conventions, converting PS values to hp would be even more confusing.

As an example, let's look at the MG ZR 160. A british car, should use bhp, right? Wrong. The 160 bhp are actually the PS value, 118 kW, which would be 158 hp, but even in the UK, what is actually PS gets called bhp. The number "158" isn't used anywhere, and to use it would prompt any newbie user to immediately revert to what he would perceive as the real value.

Now, let's take a look at the Dodge Viper SRT-10. Advertised as 500 hp (373 kW). In Europe, this would be 507 PS, but Chrysler actually keeps the original 500 hp value here, without correcting the kW (which, in Europe, would be 368).

Next, we have the Mercedes C 320. 160 kW, which are 218 PS in Europe and 215 hp in the USA.

Finally, let's see the Volkswagen Golf GTI (Mk IV). Advertised as having 180 hp, both in Europe and the USA. Strangely, the VW USA website tells us the car has 132 kW, which is 180 PS, or 177 hp.

So, my proposal is to retain the original PS values for all European and Japanese models (except for engines/models available exclusively in North America, like the 2.4L Mitsubishi Lancer), hp values for all American models (except for engines/models available everywhere else, such as 1.6L Neon and the Diesel-powered PT Cruiser) and use the kW to indicate the engine's true power. --Pc13 16:42, 2005 May 31 (UTC)

Coping with ambiguity in the term 'horsepower'

Discussion moved from Bobblewik talk but added to ongoing discussion

Will you please go back and fix all the articles you have screwed up by using they symbol "hp" for metric horsepower? See Talk:Horsepower. If you have actually gone to the trouble of disambiguating careless use of horsepower, make it clear by not using the symbol for the English units. If those are the original units, either spell out metric horsepower, or use PS for them, with that link to horsepower on first use&the metric horsepower units are discussed there. That symbol from the abbreviation of the German name is the most common form used in English for this unit, whether the cars come from Germany or Japan or Italy or wherever. Gene Nygaard

Note that my revert of "odd horsepower" was because the units were mixed in one article - kW first in some places and hp first in others. Also, it looked like you took a converted value for hp from kW and converted it back to kW, leading to precision errors. I'll take the discussion of which conversion to Horsepower, but think any discussion of mixing hp first and kW first belongs here instead. --SFoskett 14:04, May 31, 2005 (UTC)

Ah. I didn't realise that your term 'odd' meant inconsistent. Nor did I realise that you thought I had made conversion errors. I can explain both of those points. The values that I inserted came from manufacturer websites, not conversions. Sometimes the source had a hp value that differed from that already there.

For non-US vehicles the kilowatt value in official sources is often quoted as primary. The kilowatt values do not (as far as I know) vary by market. So that is convenient. The numerical hp values do vary by market. The hp values sometimes even vary within the market depending on whether it is a manufacturers press pack at launch or a manufacturers sales page at a later date. Where I could not find an official source, I made no change. The official information has eliminated some errors and improved consistency within varients. It is clear that in many cases, an engine has the same power in both markets as shown by the identical kW value. It is only the two forms of 'hp' that have different numerical values.

I hope that has given you some context. I think the official figures are an improvement. I don't like the inconsistency across models where I failed to find official values but I don't know what to do about that. Bobblewik  (talk) 14:36, 31 May 2005 (UTC)

I don't know about this article, but it is the original measurement which should come first; there are likely articles in which that varies with different measurements. That is the consistency we should strive for, not a foolish consistency in listing the units of a particular system of units first. Often we have a source which lists numbers in two different units, with one of them carried to a ridiculous precision. That one is the converted value; the other the original. Sometimes it isn't that easy to tell; it often helps to guess at whatever you know about general practices at the time, and in the locateion, where the original measurement would have been made. Note that for engine power, if you have a several different numbers in one source given in two different units, and one of those units always has whole numbers divisible by five, or by ten, that is another indication to help determine which is the original. Gene Nygaard 20:20, 31 May 2005 (UTC)

I went ahead and edited my number mungler (http://stephen.fosketts.net/tech/wikimungler.html) with this in mind. Now, when you enter PS (metric horsepower), it converts (correctly?) to hp and kW and optionally links those units to their correct wikipages. Hopefully if we start doing things like this 1001 PS (987 hp/736 kW) it will help solve this screwup. --SFoskett 21:06, May 31, 2005 (UTC)

Thanks for your comments. Although I have yet to use your number mungler, I am aware of it and appreciate your improvements in case I do use it. So far I have worked with official or at least respectable sources and the Google calculator.

As far as terminology is concerned, 'PS' and 'hp SAE' seem fine by me. I note that Morven said that hp sometimes is SAE gross and sometimes SAE net. So I am watching the debate with interest.

As far as original measures are concerned, I agree with Gene that the conversions should be secondary. The edits I have made are consistent with putting the raw value first. For example, I assumed that the best source for Mercedes Benz data was the German website. I could not find all engines specified but many were. They format power as 'kW [PS]' so I updated the article with that sequence and those numerical values. I happened to choose the term 'hp DIN' because I had seen it used elsewhere but the term could be changed easily enough. Bobblewik  (talk) 12:32, 1 Jun 2005 (UTC)

I believe that the switch from gross to net hp happened after 1970 in the USA. So generally all pre-1971 hp ratings are gross and all post-1970 ratings are net. I have some car mags from the time period, and they note gross vs. net, but this practice ceased relatively quickly once all models switched over. --SFoskett 16:27, Jun 1, 2005 (UTC)

Note that "gross horsepower" is not terminology presently used in the article itself, and we have no idea what was done differently in measuring "gross horsepower" vs. "net horsepower". Gene Nygaard 16:35, 1 Jun 2005 (UTC)

ambiguity in PS

I see that the article 'PS' says: Pferdestärke -- German for horsepower.

Is that correct? Bobblewik  (talk) 14:23, 9 Jun 2005 (UTC)

Yes, that's what PS stands for. Generally, PS now equates to metric horsepower, while "hp" and "bhp" are more ambiguous. --SFoskett 15:46, Jun 9, 2005 (UTC)

Quite. I was wondering whether the simple statement needs qualifying in that article. Bobblewik  (talk) 15:53, 9 Jun 2005 (UTC)

I don't think we need a whole lot on this disambiguation page, when it is discussed more fully in the linked article. However, it could be made a little bit clearer. I'm going to add "when PS is used as a symbol in English text, it's use is generally limited to the metric horsepower." Tweak it if you like. And maybe make the same point here in the horsepower article. Gene Nygaard 17:25, 9 Jun 2005 (UTC)