simple explanation for torque and bhp

what is the difference between bhp and torque? :confused:

when u drive fast cars and are 'thrown' back into ur seat, is that bhp or torque?

when a car accelerates quickly - what is that?

i hope someone can give a simple explanation, thanks :smile:

Reply 1

AT82

I think torque is how much pulling power you have, sort of like the strength rather than the speed. BHP is the power of the engine terms of the amount of horses you would need instead. Torque is what you need to pull stuff :smile:

Reply 2

Road Racer

As far as I know, torque is the turning force exerted hence for max acceleration you need max torque (thats why some people change gear ratios etc) and its this that throws you back into your seat. You cant have BHP without torque and vice versa, but bhp doesnt measure a force it measures the "energy output per unit time" the engine is producing. Gets quite complicated though :frown:

Reply 3

pghstochaj

This helps to explain:

http://www.pumaracing.co.uk/power1.htm

There is no really "simple" explanation apart from the defintion which isn't an explanation.

Being thrown into the back of your seat isn't just power or torque, it's also a function of the mass of the car etc. etc.

Do a search, awful lot of debate about it on the internet.

Reply 4

AT82

I have always understood torque in the concept of an electric motor. The a motor with low torque may be able to go fast in terms of RPM but may not be able cope with any weight. A high torque motor may be just fast but also will be able to start a lot quicker and pull more weight.

A low torque HIFI turntable motor tends to be quite slow to start up and cannot cope with much weight where has a high torque motor gets up to the revs an instant and can cope with much more weight.

Reply 5

OMGWTF

BHP is energy output. Torque is how much weight is behind that, how much real ummph it has

Reply 6

CityMonkey

Torque is what you get from the rotation of the crankshaft when the pistons are spinning. Torque is responsible for providing the force on the tyres to cause the car to move forward, and so it has a direct effect on it's acceleration. It's basically accounting for the transfer of rotationary movement from the piston to the wheels. The "oomph" bit is explained by how strong the explosion of the ai/fuel mixture is in the cylinder (i.e. the stronger the explosion is, the more force with which the piston is pushed down and the greater the force spinning the crankshaft so higher torque).

And BHP is the energy the engine is putting out.

As the RPM rises, the torque will drop off (thats why the faster the car is going the slower it accelerates, until eventually it stops accelerating no matter how hard you press the throttle). But at higher RPMs, the engine produces the most power.

Reply 7

Sync

In simple terms, torque is the pulling power. Very simple example: Two engines may have the same torque to pull up a 1 in 4 slope, but if one has more BHP, it will pull the car up the slope faster.

To define it properly needs a bit of maths, but think of it as:

Power = Torque x Revs

Reply 8

stevoboy

Torque is a measure of the force available to accelerate the car. Power is how much work you can do with that torque in a given time. Think of it like this : a fairly average engine produces, say, 120 ftlbs of torque. With a fairly long torque wrench or breaker bar you can also apply 120 ftlbs to something like a bolt. The difference between your arm and an engine is that you can perhaps only manage 4-5 full rotations per minute, but the engine will happily do 3500-4000 per minute.

The reason the acceleration is less at higher speed is because of 2 reasons.

1) at higher speeds you are in a higher gear. The higher gear ratio reduces the torque available at the wheels in exchange for faster rotation speed. Power available will always be the same regardless of gear (assuming same engine speed) because, ignoring any power losses in the transmission, power in = power out. Only the speed and torque are affected by gearing.

2) aerodynamic drag forces increase with the square of speed, therefore the power required to overcome the forces increases with the cube of speed (P=Fv). So to double your speed you need 8 times more power. So for example a small car with a top speed of 100mph and 75bhp, at its top speed all 75 horsepower is being used to overcome drag, and there is no surplus power to accelerate the car. So in theory to double the speed to 200mph, 8 times the power (600 bhp) would be required (obviously wouldnt work in reality cos of gearing etc).

In terms of performance, for best acceleration you need an engine which produces max torque at high revs, and suitably matched gear ratios to make best use of the available torque. For top speed, because the drag forces are so large, you need as much power as possible and taller gear ratios.

Reply 9

black_mamba

The most simple way for me is: Torque relates to the acceleration, and bhp relates to the overall picture of power and top speed.

E.g. a car has a great bhp rating but very crappy torque from its engine, you can brag all day about it doing 180mph but it would take forever to actually hit that speed, thats where torque comes in and gives you a hand.

Admittedly theres more to it than that...

Oh and that thing that throws you back into your seat? Its called inertia. Its because you were sat still but the car started moving forward OR you were moving at a certain speed but you accelerated so the car moved ahead of your body - you get slammed back into the seat. Its the same thing that makes everyone's heads bob about in unison on the bus. :wink:

Reply 10

rhythm_bandit

what does bhp stand for?

Brake Horse Power

In some instances, torque is better than BHP.
No point having a 1.2 ton vehicle with 100lb ft of torque and 300bhp, because a vehicle of 170bhp and 180lb ft torque will crap all of over it (normally, but most likely).

Torque is normally associated with the weight of the vehicle. The bigger the vehicle, generally there is more torque, apart from diesels.

You will also find torque engines are great at pulling away and getting to their maximum potential faster whereas a car optimized with bhp gather momentum unitl it peaks at a certain rpm whereas torque generally peaks at a lower rpm.

A good example is my gti6 v my brother 120d. He is faster away at the lights and come 60mph i'm passing him with ease and continuing to do so.

All other explanations of torque, you won't get better than whats written above.

Reply 13

greenmuzz

Torque's not hard to understand - it's just a turning moment and is measured in Newton Metres (or pound feet if you prefer...)- which should give a good hint as to what's going on - in essence: the amount of force that is being applied.

Think about it this way: if I have a motor with 1 Nm of torque, to which I've attatched a metre long pole, I could prevent the motor from turning by applying an opposing force of 1 newton at the end of the pole. Similarly, I would need a 300 foot pole and a one pound bag of sugar to incapacitate a 300 foot pound engine. (Actually, given the weight of the pole......).

To what extent the torque of the engine relates to the acceleration of the vehicle depends on other factors, such as gearing, traction, mass etc... but obviously, more torque is good.

As another phrase to see things: Torque is the ability of the engine to do work, power is how much work it can do

Reply 14

chaoringmeister

I Believe that torque is the turning force applied by the axle.
And the power (bHP) the the amound of energy that the engine generated per second. (in continental europe power is measured in kW which is kilajoules per second, so it makes sense)