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