drb5

iTrader: (4)

if torque is the power you want as much of as you can possibly get out the engine? what is bhp then and what does it do?

chiark

Simply put, BHP is torque * revs.

This could get very, very, very complicated very quickly, so I'm shutting up there

kazlo

jeremy clarkson said torque is as big as belgium,hope this helps

ScoobyKev

Damn good question. I thought that if a car had loads of bhp it would be fast, but thats wrong. Cus my old GT4 had 348 bhp but it wasn't that quick. But if you have loads of torque then you've definately got a quick car, its the turning force (torque) that gets you there not the bhp. So what is bhp...?

Kev

drb5

iTrader: (4)

c'mon peps. complicated is better

kazlo

drb5 , now look what you've started ,even god doesn't know what torque is

drb5

iTrader: (4)

lol. beats some of the questions that get asked on here though m8

DJB

Torque is the pulling power of the engine and varies with the engine revs. In an ideal world, this curve would be flat and as mentioned above as the revs increased, BHP would also increase in a linear way. However, in all engines the torque dips at the upper end of the rev band. This means that you eventually reach a point when the torque curve is dipping so significantly that even multiplying the high rev figure, the bhp increase tails off. So yes high torque is important but so is the shape of the torque curve. This is why gearing is so important.

D.

kazlo

dont know how it works. but a m8 has got a chipped diesel with daft torque and it seems to pull really hard from really low down the rev range, i think it's like usable power......but his bhp aint that high.does that make any sense?

drb5

iTrader: (4)

it's gettin there

akshay67

I like to think that torque is the turning force at the wheel and bhp is how long you can sustain that, or keep it going.

Take diesels. Momentary kick back, but lasts just that - a moment. Why? Not enough bhp to keep it going in one single gear. Well something like that anyway!

T5NYW

iTrader: (4)

Torque is potential energy/force applied at set Distance (d) force(f) Torque = f x d

ie I weigh 240lbs and stand on a lever 1ft long, I create a Torque of 240Lbsft.

Bhp is Peak work, Bhp = Torque x rpm

If an Engine had Torque of 240lbsft but only moved 1/4 turn
a) BHp would so low and not enough Bhp to be of use, but it still has 240lbsft Torque
b) Number 3 piston would be knackered

Torque is the potential energy available to "Kick" or "Pull" a car into motion.

Bhp is how "hard" the engine can work

Now which would be better 10 lbsft @ 40,000rpm or 40,000lbsft @ 10rpm would totally depend on your application.

IHHO AFAICR etc.

Flame suit ready

Tony

rotty

Torque is defined as "A made up term used by blokes in the pub, who drive diesels , in an attempt to convince people that their car isn't crap"

akshay67

LOL Very True!

ALi-B

iTrader: (1)

Drive a 380Bhp cossie, with similar peak torque (350ish)...
And then a 2 ton bentley with the same...BUT 600lb/ft

You'll know what it means then!

hades

In real world terms that may be true, but ultimate performance is down to bhp, weight and aerodynamics. Look at a formula 1 car, say 800 bhp at 17000 rpm, which is only 247lbft of torque. My car has more torque than that, but I wouldn't even get near in a drag race. Similarly, I can apply 150lbft with a torque wrench, but I can't push a 2.2 litre Vectra along at 130mph.

Torque is turning force. Simple Newtonian mechanics states Force = mass * acceleration. Mass of a vehicle stays constant, so turning force at the wheels is directly proportional to acceleration. (As speed increases, aerodynamic drag etc cancels out that accelerative force).

Now, torque at the wheels is directly proportional to torque at the flywheel, multiplied by the gear reduction ratio (assuming constant transmission losses). At a given constant speed, higher gear reduction ratio = higher engine rpms, again a directly proportional relationship. Do the maths, and you find everything cancels out, and acceleration is directly proportional to bhp, assuming you have chose the ideal gear ratio.

In normal driving, however, you don't have an ideal gear ratio for every single situation, and don't want to have to keep revving the engine hard to go anywhere, so you want a nice wide spread of power, i.e. a flat torque curve.

Complicated enough for you?

hades

P.S. In answer to what exactly is torque, the clue is in the units - foot pounds (or pound feet)

If you apply a torque of 250lbft to a wheel on a car, where the contact patch of the tire is exactly 1 foot from the centre of the wheel, then that wheel pushes the car forwards with a force of 250 pounds. (or backwards, before anyone says it). There are other factors that complicate the equation, but that is it fundamentally.

kazlo

eeerrrrrrrrr,so simple mechanics from newton managed to work it out,blimey everythings so much clearer now

hades

P.P.S. Tony - torque is not potential energy avaialable to kick/pull a car forward, it is the force available to kick/pull a car forward. There is (in physics terms) a subtle difference. Not meaning to flame you, and you've got all the principles right, M8.

T5NYW

iTrader: (4)

Hades,
No problem and correction accepted, with grace I did always prefered the Multiple choice questions...... A,b,C or D much easier

Not too bad seeing as I left scool 30years ago

Tony

Brit_in_Japan

As hades wrote, force = mass x acceleration. Or rearranged, acceleration = force/mass

Torque is the rotational force that is developed by the engine. That torque is converted to the force exerted by the tyres on the road by the transmission, differentials etc.

The acceleration of a car is directly related to the net force exerted on it. In other words torque generated by the engine minus any forces acting to oppose motion (wind resistance, friction etc). Acceleration is also inversely proportional to the mass, the higher the mass - the lower the acceleration for a given force. So torque/mass ratio is key for acceleration.

Power is the rate at which force (or torque) is delivered. So a petrol engine delivering maximum torque at a high engine speed (e.g. 6000 rpm) will have a much higher power figure than a diesel engine developing the same torque at a lower engine speed (e.g. 2500rpm). But the diesel engined car would out accelerate the petrol engined car for all engine speeds where the torque of the diesel is higher than the torque of the petrol, assuming mass and gearing are the same.

Adam M

but gearing isnt the same because if it was the diesel would only be able to do 60mph flat out because it can only rev to 3500.

The way to think of it is to imagine 2 guys riding bikes. One is built like a **** house and has tree trunks for legs, the other is a scrawny weed, but aince his legs weigh nothing, he can turn them much faster.

Now bring in the fact that the racing bike has gears and you understand.

the big legs can turn much harder, so you can put them in a higher gear but they are limited by how fast they can turn.

The scrwany legs need a low gear otherwie they can't ove at all, but low gears mean they have to turn a lot faster to produce the same acceleration of the bicycle.

In terms of out right capability, the scrawny guy can end up being faster (honda S2000 F1 car), the muscley guy could compensate buy having loads of gears to make his turning power useful (HGV) but extra gearing gives more changes and makes the mechanics even heavier.

jmk

You want loads of low down torque and bucket fulls of BHP higher up the rev range.

Which ever way you look at it, you can never have too much of either as you're always left wanting more, more, more.

Brun

You need masses of BHP so you can keep the pub conversation going

Mycroft was all torque wasn't he?

drb5

iTrader: (4)

lol at brun

i used to think of torque as the one that would be able to snap a (example) flywheel a:_because of the thing not being able to turn quick enough-: and bhp being the one that'll keep it turning for longer

ShyTot

The best description I have ever read can be found here: -

http://www.seatcupra.net/guides.php?descrip=Power%20And%20Torque

[Edited by ShyTot - 11/28/2003 1:11:14 PM]

bobbyh

IMO

read that your average artic diesel tractor develops peak torque between a power band of 1.0k - 1.6k rpm!!....thats why they have so many fecking gears.

OllyK

Bloody hell ShyTot

Somebody print that lot off and publish as a book on torque / bhp! Very imformative however!!

[Edited by OllyK - 11/28/2003 12:35:36 PM]

ShyTot

I didn't write that, it's just the best description I've ever read

And now I actually understand the difference....

OllyK

Tut tut - not siting your references!!