BHP vs PS

Pep

hi all,

Can anyone tell me the difference between measuring a cars power in BHP and PS. VW seem to use BHP and Ford use PS. How do you compare the numbers?

Thanks

daedalus2097

PS stands for the German for horsepower (can't remember the translation now) but they're roughly equivalent. I think PS is slightly higher, but it's only around 2% or less, so 1 PS roughly equals 0.98 HP. BHP just means HP which is measured at the flywheel rather than the road wheel.

PauloMN

Some further info here:
http://malaysia.answers.yahoo.com/question/index?qid=20070715124014AAhTYDf

Lex Luthor

PS = PferdeStärke which is German for Horse Power

Pep

Thanks for the replies lads. It seems strange that VW don't use the german term!

Plug

On this bombshell can people explain in simple what is torque or torques are clarkson calls them. Its a bit like horse power thats all i know......i think.

bigtimecharlie

From what I have been told, BHP is the power of the engine as tested on a bench ( generally measured at the flywheel) while "Torque" is the full movement pressure measured at the driven wheel's ( takes into account the engine, the gearbox and the final drive).

I imagine a more technical explanation will follow this is the simple one line answer.

Plug

I don't think i will ever find out what it it:D

JHMEG

Simply put: torque is the ability to do work. Power is the rate at which the work can be done.

Eg. Transit van, high torque, low power. Can pull a fairly big load, but not very fast.
Eg. Civic Type-R, low torque, high power. Can't pull much of a load, but what it can pull (itself, which is fairly light) very fast.

Lord Nikon

Is maith liom PS.

TomMc

In simplistic terms

More BHP = Faster Car - i.e. Higher Top Speed.

More Torque = Better Pulling Power - i.e. Quicker Acceleration.

___

BHP makes a car fast, but torque makes it quick.

colm_mcm

torque is cheap.

MAYPOP

The story goes that German horses were slightly smaller than their British equivalents, which is why there is a small difference between PS and HP.

colm_mcm

it's to do with the Germans using the metric system isn't it?

tuxy

TomMc wrote:

More Torque = Better Pulling Power - i.e. Quicker Acceleration.

So how come a car like a Honda civic type r that has fairly low torque has very fast acceleration?

colm_mcm

not in 4th or 5th at low speeds it hasn't. car has to be revved hard to get fast acceleration.

bushy...

Plug wrote:

I don't think i will ever find out what it it:D

It makes it a bit easier to understand if you know/think of

1 HP ~ = 750 watts ~= 33,000ft-lbs/min

HP&torque are tied together , so if you have an engine making X horsepower and you want more , you can either make it produce more force ( turbos/superchargers/nitrous/gasflows/timing/fuels/compression etc) or make it produce it more often ( higher rpm)

nastysimon

Plug wrote:

On this bombshell can people explain in simple what is torque or torques are clarkson calls them. Its a bit like horse power thats all i know......i think.

Ultimately:
Power = Torque x RPM

Obviously, you have to use the right units, but that's the relationship.
If you increase your torque at a given RPM, you also increase the power at that RPM too. When people talk about torque, they are usually talking about lower down torque (between about 2000 and 4000 rpm in a petrol engine). By increasing this, you increase the flexibility of your engine, but often the trade-off is that you get less top end torque, or even ability to rev to the top end (lower red-line), so ultimately less maximum power, but more power where you use it most (but not necessarily more where you need it most).
Fast bike's engines produce lots of power (at least for their capacity) by revving very fast, but they also produce little torque, so they are not suitable for pulling heavy loads at low engine speeds (which car engines have to be).

You'll find that most naturally aspirated engines (not turbo/super charged) that are really powerful for their capacity (high specific output) will produce that power at high engine speeds and most likely have a larger bore than stroke. They'll also be less flexible and therefore less relaxed to drive than a similar capacity engine with a longer stroke and smaller bore, though there are some technologies which help level the playing field a little, such as variable valves and variable inlet plenums.

A torquey engine is a joy to drive (relaxed and flexible), but does not excite as much when being pushed hard. For the vast majority of people a torquey, flexible engine will be quicker.

Balfa

Plug wrote:

On this bombshell can people explain in simple what is torque or torques are clarkson calls them. Its a bit like horse power thats all i know......i think.

Oh god, no...
Feel free to read my delightfully nerdy ramblings on this at http://www.boards.ie/vbulletin/showthread.php?t=249343&page=4.

I'd like to point out that, since that post, I've revised my opinion of power:

Since the ultra-important final word on an engine's performance is the area of the torque curve in the portion of engine speed that's actually used, it turns out that torque peak is no more important than torque width (since area = width x height). And while torque peak may not tell you much about the shape (and hence area) of the torque curve, the power peak is probably a more useful number if you had to distill everything to one number.

This is because power is proportional to torque x engine speed, and thus if it has high peak power, it means the engine either produces lots and lots of torque at low speed (small width) or modest torque at very high engine speeds (large width), OR anything in between (medium torque at medium speed, etc.). All engines would result in the same thing: gofasterness.

Don't make me draw another graph!!

JHMEG

colm_mcm wrote:

not in 4th or 5th at low speeds it hasn't.

Hence Honda gave it 1st, 2nd and 3rd!

Mayshine

Don't forget to add gearing to your model,

The torque produced by the engine is multiplied by the gears to give your wheel torque. Thats what you feel.

Ist gear in the civic type r is a bigger torque multiplier than than first in a diesel car, but the extra revs of the type r allows a similar road speed for the given gear.

Shorter gear = more torques at the wheel.

colm_mcm

JHMEG wrote:

Hence Honda gave it 1st, 2nd and 3rd!

I'm not criticising the car, just explaining how it can accelerate fast despite not having much torque.

E92

colm_mcm wrote:

it's to do with the Germans using the metric system isn't it?

Surley the metric system for power is kilowatts(kW)? Certainly the SI unit of power is the Watt. I seem to remember the EU wanting to issue a directive which wanted to get rid of references to power in bhp/PS and instead in kW, but fortunately nobody understood what kW were in cars, hence why bhp/PS are still used throughout Europe even to this day.
I didnt know that there was an actual difference between bhp and PS. I know that the 110 PS Mondeo actually produces 108 bhp, but then we have Volkswagen, with the 115 PS Golf in the UK and the 115 bhp Golf here, so I always assumed they were the same. Anyway, the difference is so small as to be insignificant.

In simple English, and to the best of my knowledge, power is the thing that gives the 0-60 and top speed times, whereas torque is the thing that makes a car overtake on a motorway.

peasant

The original "horse power" measured the amount of water one horse could pump up from a deep mineshaft in a certain amount of time, driving the pump by walking around in a circle.

They needed a reference to compare the then "new" steam engines to something they knew. So, one horse driving the pump could bring up so many gallons per hour, the steam engine could do ten times as much, hence it had ten hp.

If you were to measure torque, you would be interested in which would be the maximum weight that that horse could move in one single pull (over a set distance) instead of the continuous movement of the pump.

And to confuse matters even more ...


...an early steam engine may have been able to lift ten times as much water in an hour than the horse, but the horse would still have managed to pull a far heavier weight from standstill than the engine

Oryx

I was told torque was the turning force of the engine. But I could never quite get my head around it either.

colm_mcm

E92 wrote:

Surley the metric system for power is kilowatts(kW)? Certainly the SI unit of power is the Watt. .......

A horse power was defined by Watt as 33,000 foot pounds of work per minute. (roughly 745 watts)

I presume that if you use the nearest metric equivelant of 33,000 ft/lb it works out at roughly 735 watts. hence the difference in hp and PS. I may be wrong.

JHMEG

E92 wrote:

power is the thing that gives the 0-60 and top speed times, whereas torque is the thing that makes a car overtake on a motorway.

A fairly accurate approximation. Torque, due to the increased load from wind resistance, comes more into play at higher speeds.

Altho, it's all relative. A Civic Type R will have no problem overtaking at motorway speeds. And will do so quicker than a Transit because of better aerodynamics and a lot more power.

maidhc

I have a fantastic booklet somewhere published by Massey Ferguson in the 70's called "Horse power". It does a great job of comparing and contrasting HP and torque. For its comparisons it used a Motorbike and a tractor.

If I can find it I will scan up a few pages.

colm_mcm

I'm pretty sure they made the tractor look better...

maidhc

colm_mcm wrote:

I'm pretty sure they made the tractor look better...

P1: Motorbiker passing out tractor on a road
P2: Tractor firing sh1te all over a biker going through a field

Its a good booklet though.

Can't find it right now

colm_mcm

I remember my physics book compared a F1 car and a tractor to show difference between torque and hp

Balfa

JHMEG wrote:

A fairly accurate approximation. Torque, due to the increased load from wind resistance, comes more into play at higher speeds.

Altho, it's all relative. A Civic Type R will have no problem overtaking at motorway speeds. And will do so quicker than a Transit because of better aerodynamics and a lot more power.

A completely inaccurate approximation, by both yourself and E92. Seriously, power is what gets you from 0-60, and torque is what gets you from 0-60, and power is what lets you overtake at motorway speed, and torque is what lets you overtake at motorway speed. They're just two different ways of looking at the same thing.

And engine doesn't discard one rule of physics and adopt another above a certain speed.

colm_mcm

looking at a dyno readout of power and torque curves can be helpful

crazylady333

hey thanks colm_mn, finally got it..an hour later..dnt think this site likes me

JHMEG

Balfa wrote:

And engine doesn't discard one rule of physics and adopt another above a certain speed.

If running in a vacuum, or on a bench.

Powering a vehicle introduces wind resistance into the equation which changes things. A torquey transit will not overtake a low torque CTR at any speed.

Stick the transit engine in the CTR and I doubt it will be able to overtake a real CTR either. Power matters at all speeds.

Plug

Balfa wrote:

A completely inaccurate approximation, by both yourself and E92. Seriously, power is what gets you from 0-60, and torque is what gets you from 0-60, and power is what lets you overtake at motorway speed, and torque is what lets you overtake at motorway speed. They're just two different ways of looking at the same thing.

And engine doesn't discard one rule of physics and adopt another above a certain speed.

Thank you sir! That sounds about right.

maidhc

JHMEG wrote:

If running in a vacuum, or on a bench.

Powering a vehicle introduces wind resistance into the equation which changes things. A torquey transit will not overtake a low torque CTR at any speed.

Stick the transit engine in the CTR and I doubt it will be able to overtake a real CTR either. Power matters at all speeds.

And try putting a CTR engine into a fully loaded transit...

I am a lawyer, not a physicist, but:

Torque is force

Power is force x speed

A CTR will develop maximum power and probably torque at (say) 10000rpm, if the engine was pulling a load of pallets up a hill the speed would fall and the torque drop off would be so significant the engine would stall. (unless the shortcoming was overcome with gearing... but you still have the issue of the longevity of an engine that buzzes at 10000rpm etc)

A transit however will develop maximum power at 4000rpm, and maximum torque at 1800 rpm. As it looses speed going up a hill this will be counteracted by an increase in torque so it will just stay lugging.

More torque means the engine can develop more force at the crankshaft. An engine with more torque will thus generally be much heavier and stronger. That is why the 7.5L cast iron lump in my tractor probably weighs more than a small car but only develops 130hp at 2000rpm.

Altreab

maidhc wrote:

And try putting a CTR engine into a fully loaded transit...

I am a lawyer, not a physicist, but:

Torque is force

Power is force x speed

A CTR will develop maximum power and probably torque at (say) 10000rpm, if the engine was pulling a load of pallets up a hill the speed would fall and the torque drop off would be so significant the engine would stall. (unless the shortcoming was overcome with gearing... but you still have the issue of the longevity of an engine that buzzes at 10000rpm etc)

A transit however will develop maximum power at 4000rpm, and maximum torque at 1800 rpm. As it looses speed going up a hill this will be counteracted by an increase in torque so it will just stay lugging.

More torque means the engine can develop more force at the crankshaft. An engine with more torque will thus generally be much heavier and stronger. That is why the 7.5L cast iron lump in my tractor probably weighs more than a small car but only develops 130hp at 2000rpm.

But how much torque and at what engine speed?

*grabs me coat

Balfa

JHMEG wrote:

If running in a vacuum, or on a bench.

Powering a vehicle introduces wind resistance into the equation which changes things. A torquey transit will not overtake a low torque CTR at any speed.

Stick the transit engine in the CTR and I doubt it will be able to overtake a real CTR either. Power matters at all speeds.

Okay, so by completely ignoring my point earlier about the AREA of a torque curve, you win. Or not...
You say a Transit is torqueier (let's not say that word again) than a CTR, and that's because you (and everyone else) looks at the PEAK torque number. That's understandable, because it's the only number the marketing bods give you, because they don't know any better, either.

I propose that the Civic actually has more torque, and here's why:

If you google image for type-r dyno, you'll see that a typical civic type-r engine produces, let's say an average of about 105ft.lb (142Nm) from 2,500rpm to about 8,000rpm. That's a total width of 5,500rpm. If you multiply the height by the width to get the area, you end up with 781,000.

I couldn't find a dyno graph for a transit (I suppose nobody cares ), but the top level diesel gives 375Nm @1900rpm, so let's suggest that it produces an average of 370Nm from 1000 to 3000rpm (a "powerband" width of only 2000rpm). Multiplying again, we get only 740,000.

So, actually less torque. Not a huge difference, but the point remains. Everything else can be controlled by gearing. Give the Transit 8 very short gears with f1-speed gearshifting, and it'll blow past a civic all the way up to its 8th gear redline at 80km/h

Let's not forget that a transit, with maybe twice the frontal area of a civic, will require twice the torque to overcome wind resistance at speed. And with 1.5 times the mass (is that all? I was surprised!), will require 1.5 times the torque to accelerate its own weight.

If you put the transit engine into the civic with the appropriate gearbox, it'll make the civic a little heavier and, as we've seen above, will have a little less torque and, therefore, will be slower than a stock civic.

if, on the other hand, you put the civic engine with the appropriate gearbox into the transit, the transit will be a little lighter, and have a little more torque, and will outrun a stock transit. And the engine won't really snot itself any more than if it was run flat out in the civic, thanks to the short gearing giving it a break in the heavy transit.


Notice the way I didn't mention power anywhere?

JHMEG

Ok, I'll put it to ya this way:

Transit engine in CTR with CVT gearbox that keeps it at peak torque (1900rpm).

CTR with CTR engine, CVT gearbox that keeps it at peak power (7800rpm).

Which will be quicker to 100 mph?

Balfa

JHMEG wrote:

Ok, I'll put it to ya this way:

Transit engine in CTR with CVT gearbox that keeps it at peak torque (1900rpm).

CTR with CTR engine, CVT gearbox that keeps it at peak power (7800rpm).

Which will be quicker to 100 mph?

Sorry, re-reading my earlier post now, I probably missed your point when I was writing it...

First of all, the answer: the CTR engine.

For a constant speed (with constant wheel size, that means constant wheel speed), you can divide the engine speed (and hence multiply the torque) much more at 7800rpm than you can at 1900rpm. When the gearbox multiplies the torque of the engine, the effective torque at the wheels goes up. Let's pretend, to make it easy, that the wheels are spinning at 1900rpm (134mph with my mazda's 14" wheels!). The 1900rpm engine is going through a 1:1 gear ratio, so its torque is multiplied by one. Because the engine turning at 7800rpm is turning four times faster than the engine turning at 1900rpm, you get to divide its speed (multiply its torque) by 4. When you multiply a CTR's torque at 7800rpm (156Nm) by four, you get 624Nm laid onto the road... Much higher than the transit engine's 375Nm at the road.

That's why peak horsepower is so popularly quoted... it's a combination of torque and rpm... in effect, it's the point after which torque drops off too rapidly to benefit from longer gearing and before which the rpm is too low to allow sufficient torque multiplication.

JHMEG

Very informative!

So if I can get my engine to spin to 17,000 rpm (twice the current max), I'll be putting down 2x the torque. I feel a project coming on!

I get the impression from your explanation that you may have dispelled the theory from the diesel advocates that diesel engines have "better overtaking ability due to mid range torque"? ie a diesel spinning at 4,000 rpm (ie close to the upper limit) is putting down significantly less torque than a petrol spinnning at 7,000 or 8,000 rpm, owing to the multiplier effect of the gearing?

Balfa

JHMEG wrote:

Very informative!

So if I can get my engine to spin to 17,000 rpm (twice the current max), I'll be putting down 2x the torque. I feel a project coming on!

Assuming you can keep the torque curve flat up that high, AND you modify the gears appropriately, sure
People often don't pay much attention to gear ratios (again, it's not something that marketing bods care about), but they are, of course, quite significant. After I test-drove, but before I bought my Mazda, I tried a 2001 Geo Prizm (rebadged Corolla) and despite having a very high-tech 1.6 litre, 123hp engine, it felt awfully sluggish compared to the 105hp, similarly-sized Mazda. Before long I realised the automatic transmission was a freakin 3-speed!

That said, if performance was the only reason people bought cars, we'd all be driving 7-speed close-ratio semi-automatics. Usually, the manufacturer tries to set up the ratios so that at about 65mph, the engine is at its best efficiency (usually around 2,000rpm, depending on per-cylinder size among others - my poor Mazda buzzes at over 3,000 at that speed ), and then they fit all the other gears around that.
On second thought, it wouldn't surprise me if they tried to have the engine running most efficiently at 55mph, at least over here, because that's the speed that the govt. tests the highway fuel economy at, so the old marketing fellas get to publish marginally higher figures at the expense of ACTUAL fuel economy that you'd get if you drove at a more realistic 65mph

I get the impression from your explanation that you may have dispelled the theory from the diesel advocates that diesel engines have "better overtaking ability due to mid range torque"? ie a diesel spinning at 4,000 rpm (ie close to the upper limit) is putting down significantly less torque than a petrol spinnning at 7,000 or 8,000 rpm, owing to the multiplier effect of the gearing?

Yeah, even though I'm a diesel advocate (because of fuel economy per hp!). Because of the higher torque across the rev range, they can get away with longer gearing, which more significantly multiplies the wheel speed and divides the torque at the wheels than petrol.
I think the misconception may come from the fact that at cruising speeds, diesels are already at the start of their power band, so just mash the pedal and off you go... It's a satisfying experience.
Petrols are usually well below their powerband (too highly geared) at cruising speeds, so unless they downshift, they're not going anywhere fast. But if you do drop to 3rd in a Type-R, you're going to snot past most diesels. Not a 123d, though. Mmmmm... 123d....

That said, it may have been different in the past when cars really did have peak torque at some particular rpm. Most modern engines, especially with cvvt and stuff, achieve close to peak torque throughout the revs.

JHMEG

Balfa wrote:

65mph, the engine is at its best efficiency (usually around 2,000rpm, depending on per-cylinder size among others - my poor Mazda buzzes at over 3,000 at that speed

LOL. My DA6 would be at 4,500 rpm at that speed, in 5th! All 5 gears very short, max theoretical speed in 5th being about 120mph @ 8,000rpm (Jap speed limited cuts in slighty before that tho).

Yeah, downshifting is all part of the fun of driving a petrol. Not into downshifting to overtake, well maybe time to start thinking about what kind of slippers would be comfy...

maidhc

JHMEG wrote:

Yeah, downshifting is all part of the fun of driving a petrol. Not into downshifting to overtake, well maybe time to start thinking about what kind of slippers would be comfy...

You don't like diesels or cars that are not made by honda, which is fine, but diesels do have their advantages... there are certainly no petrol cars on the road that can return 55mpg + over a full tank and still have reasonable power for real world (non racetrack) driving.

(cue the hybrid argument.... )

JHMEG

maidhc wrote:

You don't like diesels

Understatement! The work of satan...

maidhc wrote:

or cars that are not made by honda

True, I would consider myself a Honda fan, but there are many non-Honda cars that I wouldn't mind owning.. GTR-R34, Z06, certain Mustangs and American muscle cars in general...

maidhc wrote:

there are certainly no petrol cars on the road that can return 55mpg + over a full tank and still have reasonable power for real world (non racetrack) driving.

A diesel that does over 55mpg would be what, a 1.8 or so. That's awful small for a diesel, and would be zero fun to drive. Slippers time again...

Balfa

JHMEG wrote:

A diesel that does over 55mpg would be what, a 1.8 or so. That's awful small for a diesel, and would be zero fun to drive. Slippers time again...

Did I not just say 123d? 54.3mpg and more hp than a Civic Type-R.

JHMEG

Balfa wrote:

Did I not just say 123d?

...which doesn't actually exist.

It'd be cool if they did pull it off tho.

Balfa

JHMEG wrote:

...which doesn't actually exist.

It'd be cool if they did pull it off tho.

It exists, they did pull it off, you'll be able to drive one in November. They're probably already taking orders.

JHMEG

By pull it off, I mean that it's actually a good, usable engine. If massive boost comes in high up in the rev range, well they can say it's 200 odd bhp, but it won't be usable.

It wouldn't be the first time a car didn't live up to the pre-launch hype spun out by the manufacturer.

Having said that, I hope they do actually do a good job of it. It will be a fair achievement.

(How does a 30mpg 5.0 litre 500bhp V10 normally aspirated petrol engine compare?)

maidhc

JHMEG wrote:

If massive boost comes in high up in the rev range, well they can say it's 200 odd bhp, but it won't be usable.

Like a type R....?