Discussion
This one came up on a forum/mailing-list I was on before, and I still never truely understood the differences correctly...
I'm sure someone here can explain what each one is - which is better (higher bhp or higher torque) etc etc...
Also one thing that I am interested in, what characteristics of an engine give a higher figure for each?
-andy-
I'm sure someone here can explain what each one is - which is better (higher bhp or higher torque) etc etc...
Also one thing that I am interested in, what characteristics of an engine give a higher figure for each?
-andy-
Rather than go into detail here let me direct you to an expert. See www.pumaracing.co.uk and look at the pages power1, power 2 etc.
Edited to add the web page does not seem to work this morning. Maybe later!
>> Edited by kevinday on Tuesday 5th November 07:27
Edited to add the web page does not seem to work this morning. Maybe later!
>> Edited by kevinday on Tuesday 5th November 07:27
In simplistic terms, torque gives you flexibility and power gives you speed.
Of course it isn’t quite as straightforward as that, but I’ll try to illustrate the point by comparing cars.
Let’s start with Alfa Spyder and the Honda S2000. Both have 2-litre 16 valve engines, but the Alfa does 131mph while the Honda does 150mph. Aerodynamics and gearing have an effect, but the main reason for this difference is that the Alfa has 150bhp whereas the Honda has 237bhp. More power, more speed.
The reason it makes so much more power is because it revs higher (the Alfa’s max power being at 6,200rpm whereas the Honda’s is at 8,300rpm). As Keith Duckworth of Cosworth fame once said, the amount of power you get out of an engine equals the size of the bang times the number of bangs per minute – which is why current F1 engines do 18,000+rpm.
Now let’s bring torque into the picture by comparing the S2000 to the 4-litre TVR Chimaera. Both have similar top speeds and similar power outputs (152mph and 240bhp for the TVR).
But compare the torque. The Honda produces just 151lb/ft and needs 7,500rpm to do it, whereas the TVR produces 270lb/ft and does it at just 4,000rpm. This extra torque is due to the engine’s extra cubic capacity and torque affects the way cars accelerate.
Make full use of the revs and the gears and there wouldn’t be much in it, the Honda doing 0-60 in around 6 seconds against about 5 seconds for the TVR, though the fact the TVR is nearly 200kg lighter is a major factor in that.
But say you were stuck behind a car doing 40 mph, then hit a dual carriageway and pulled out to overtake without changing down from top. The Honda’s lack of torque means it would only accelerate quite slowly, whereas the high torque of the big V8 would get the TVR up to the limit much more quickly. In other words, more torque means you don’t have to work the engine so hard to get you moving faster.
Hope this has helped.
Of course it isn’t quite as straightforward as that, but I’ll try to illustrate the point by comparing cars.
Let’s start with Alfa Spyder and the Honda S2000. Both have 2-litre 16 valve engines, but the Alfa does 131mph while the Honda does 150mph. Aerodynamics and gearing have an effect, but the main reason for this difference is that the Alfa has 150bhp whereas the Honda has 237bhp. More power, more speed.
The reason it makes so much more power is because it revs higher (the Alfa’s max power being at 6,200rpm whereas the Honda’s is at 8,300rpm). As Keith Duckworth of Cosworth fame once said, the amount of power you get out of an engine equals the size of the bang times the number of bangs per minute – which is why current F1 engines do 18,000+rpm.
Now let’s bring torque into the picture by comparing the S2000 to the 4-litre TVR Chimaera. Both have similar top speeds and similar power outputs (152mph and 240bhp for the TVR).
But compare the torque. The Honda produces just 151lb/ft and needs 7,500rpm to do it, whereas the TVR produces 270lb/ft and does it at just 4,000rpm. This extra torque is due to the engine’s extra cubic capacity and torque affects the way cars accelerate.
Make full use of the revs and the gears and there wouldn’t be much in it, the Honda doing 0-60 in around 6 seconds against about 5 seconds for the TVR, though the fact the TVR is nearly 200kg lighter is a major factor in that.
But say you were stuck behind a car doing 40 mph, then hit a dual carriageway and pulled out to overtake without changing down from top. The Honda’s lack of torque means it would only accelerate quite slowly, whereas the high torque of the big V8 would get the TVR up to the limit much more quickly. In other words, more torque means you don’t have to work the engine so hard to get you moving faster.
Hope this has helped.
The most simple explaination I've heard for the difference between 'power' (BHP) and torque is .....
Imagine your riding a bicycle, when you start off you push down on the pedal and slowly move away and build up speed as you begin to pedal faster ..... the force you are putting through he pedals is torque!
Then you come to a nice gradual down hil section and you pedal as fast as you can, you get to a stage where you just can't pedal any faster ....... you have reached your maximum power!
Bloody simple I know, but it helped me understand
!!!!!!!
Imagine your riding a bicycle, when you start off you push down on the pedal and slowly move away and build up speed as you begin to pedal faster ..... the force you are putting through he pedals is torque!
Then you come to a nice gradual down hil section and you pedal as fast as you can, you get to a stage where you just can't pedal any faster ....... you have reached your maximum power!
Bloody simple I know, but it helped me understand
!!!!!!!
plipton said: As mentioned before and a good quote; Torque wins prizes, BHP sells cars. Sad but true !!
I agree except I bet a formula 1 car has crap torque.
However a torqey car will be much more drivable a thus faster on the road.
Maybe a better way of recording an engines performance would be to take the BHP average over a % of the redline.
2 links from how stuff works, no doubt more there
www.howstuffworks.com/horsepower.htm
http://www.revsearch.com/dynamometer/torque_vs_horsepower.html">www.howstuffworks.com/framed.htm?parent=horsepower.htm&url=http://www.revsearch.com/dynamometer/torque_vs_horsepower.html
www.howstuffworks.com/horsepower.htm
http://www.revsearch.com/dynamometer/torque_vs_horsepower.html">www.howstuffworks.com/framed.htm?parent=horsepower.htm&url=http://www.revsearch.com/dynamometer/torque_vs_horsepower.html
I agree except I bet a formula 1 car has crap torque.
800 BHP @ 17000RPM = 247 lbft at that engine speed (although peak torque is probably in excess of 300 lbft + at lower RPMs). Unfortunately I have no figures for F1 engines other than what Murray Walker used to blurt out at regular intervals.
Still - that's quite a lot of torque for a car weighing less than a nat's todger ;-)
Jeepers - that's more than my chimp 450 makes and that weighs 1040 kilos !!! Suddenly I have an overwhelming urge to drive Herr Schumacher's Ferrari.
Michael....if you're reading this, my phone number is............
Good guess, yes it does. This only applies if torque is measured in lbs/ft and not in nM or other metric measures. This also means that if you plot torque and bhp on a graph from several engine speeds, then the lines will cross at 5252 rpm (torque will be higher than bhp under 5252 rpm and lower above 5252rpm).
Here's my 2 cents worth. It's a bit long winded, but hopefully it encapsulates everything on here...
First, power, what do we mean by that?
Well, we usually express power in terms of the amount of time it takes to do a certain amount of work... for example, one horsepower is measured as the amount of work required to lift 33,000 lbs over 1 foot in 1 minute (huh -that's obvious ?!!). As this is such an obviously Scottish measurement (as James Watt first devised the calculation) , we have a metric equivalent... the metric horse could lift 4,500Kg a metre in a minute... 98.6% of a good English horse. The Europeans decided to call it a PS (Pferde Starke - German for Horse power!)instead of an HP to cover their shame. Also, in the newfangled metric system, 1hp is the equivalent of 746 Watts of electrical power. So, to recap briefly:
1 HP = Roughly the amount of work a horse can do lifting coal up a mineshaft, assuming his heart was really in it = 1.014 PS = 0.746 KW - easy !
Now we need a way to measure this output - so we use a defined force or "brake" to see how much energy we need to apply to stop it - Hence "Brake Horsepower" - and is defined as it's maximum performance at a certain rpm.
The other thing we babble on about is Torque... Torque is the amount of force applied to turn something multiplied by the distance from the axis of it's rotation... sounds all weird, until you realise that we use the engine to rotate the front wheel, so torque is something that would be nice to calculate. Something interesting is that 1hp is 550ft/lbs of torque per second.
Now, it's fairly easy to measure torque... this is where the dyno comes in, and we calculate horsepower from an engine's torque output multiplied by the revs...
A dynomometer is just a heavy drum (brake), an accelerometer and a computer... if you know the weight of the drum, and you know how fast it's being accelerated, you can calculate the torque that must be being applied to the drum. What you also want to take into account are the frictional losses on the drum, and the air temperature at the time (which is why you'll see air temperature, pressure and a correction factor calculated by the software... as air temperature goes up, so the effective power output goes down, so the correction factor has to go up to normalise this).
Taking a Dyno Run
So, to measure torque, we strap the car to the dyno, start it up and run it up in the gears to 3000RPM the dyno operator holds the car at a steady 3000 for 6-7 seconds and the dyno learns the road speed for that car at 3k. ( Some dynos use an inductive loop to accurately measure RPM - but the rev counter method works fine for most modern cars) - now with a given road speed the RPM can be calculated.
... cars tend to do their power runs in 4th gear, as it's the best gear for acceleration at speed and less chance of the wheels slipping, as the calculation errors get smaller the bigger the numbers are. 4th is used because on cars these days 5th gear tend to be a bit of an overdrive.
The throttle is gently floored, and the dyno slowly allows the speed of the engine to increase - this measures the torque of the engine. When the engine reaches maximum RPM, the operator puts the car in neutral, and allows the wheels to decelerate of their own accord - this measures the losses of the transmission,driveshafts,bearings brakes (if they are sticking) and tyres
Now here comes the maths
BHP = Torque (lbft) x RPM
-------------------
5252
This means that BHP is always equal to torque at 5252rpm - if its not then there is something wrong!
Now using a sample we get max power of 169.3BHp @ 7869RPM but 115.0lbft of Torque. The important factor here is that it makes its maximum power at nearly 8000rpm!
The moral of this essay is - it is better to make torque at high RPM for a screamer! - and thats why beause Hondas rev so high they produce the power!
I realise I've forgotten an important part of the calculation
Where did the 5252 figure come from ?
As discussed what we actually measure is torque, expressed in ft/lb, and then we calculate actual horsepower by converting the twisting force of torque into the work units of horsepower.
Visualize a one pound weight, one foot from a fulcrum on an "invisible weightless" bar. If we rotate that weight for one full revolution against a one pound resistance, we have moved it a total of 6.2832 feet (pi times a two foot circle), and, we have done 6.2832 foot pounds of work.
OK. Remember James Watt? He said that 33,000 foot pounds of work per minute was equivalent to one horsepower. If we divide the 6.2832 foot pounds of work we've done per revolution of the weight into 33,000 foot pounds, we come up with the fact that we have to rotate that weight at the rate of 5,252 revolutions per minute in order to do 33,000 foot pounds per minute of work, and thus do work at the equivalent rate of one horsepower.
Therefore, the following formula applies for calculating horsepower from a torque measurement:
Horsepower = ( Torque * RPM ) / 5252
Thats where the 5252 comes from.
Torque is only half the story. While torque is the force created, it doesn't account for the importance of revs.
Imagine trying to remove a wheel nut from a car with a standard wheelbrace and all the torque you could produce can't loosen the "Kwik fit special" airgunned super tightened wheel bolts. You apply lots of force, i.e. torque, but you still can't generate any rpm. Therefore nothing is accomplished, no power generated despite your cursing and kicking. So - Without rpm, torque is useless!
First, power, what do we mean by that?
Well, we usually express power in terms of the amount of time it takes to do a certain amount of work... for example, one horsepower is measured as the amount of work required to lift 33,000 lbs over 1 foot in 1 minute (huh -that's obvious ?!!). As this is such an obviously Scottish measurement (as James Watt first devised the calculation) , we have a metric equivalent... the metric horse could lift 4,500Kg a metre in a minute... 98.6% of a good English horse. The Europeans decided to call it a PS (Pferde Starke - German for Horse power!)instead of an HP to cover their shame. Also, in the newfangled metric system, 1hp is the equivalent of 746 Watts of electrical power. So, to recap briefly:
1 HP = Roughly the amount of work a horse can do lifting coal up a mineshaft, assuming his heart was really in it = 1.014 PS = 0.746 KW - easy !
Now we need a way to measure this output - so we use a defined force or "brake" to see how much energy we need to apply to stop it - Hence "Brake Horsepower" - and is defined as it's maximum performance at a certain rpm.
The other thing we babble on about is Torque... Torque is the amount of force applied to turn something multiplied by the distance from the axis of it's rotation... sounds all weird, until you realise that we use the engine to rotate the front wheel, so torque is something that would be nice to calculate. Something interesting is that 1hp is 550ft/lbs of torque per second.
Now, it's fairly easy to measure torque... this is where the dyno comes in, and we calculate horsepower from an engine's torque output multiplied by the revs...
A dynomometer is just a heavy drum (brake), an accelerometer and a computer... if you know the weight of the drum, and you know how fast it's being accelerated, you can calculate the torque that must be being applied to the drum. What you also want to take into account are the frictional losses on the drum, and the air temperature at the time (which is why you'll see air temperature, pressure and a correction factor calculated by the software... as air temperature goes up, so the effective power output goes down, so the correction factor has to go up to normalise this).
Taking a Dyno Run
So, to measure torque, we strap the car to the dyno, start it up and run it up in the gears to 3000RPM the dyno operator holds the car at a steady 3000 for 6-7 seconds and the dyno learns the road speed for that car at 3k. ( Some dynos use an inductive loop to accurately measure RPM - but the rev counter method works fine for most modern cars) - now with a given road speed the RPM can be calculated.
... cars tend to do their power runs in 4th gear, as it's the best gear for acceleration at speed and less chance of the wheels slipping, as the calculation errors get smaller the bigger the numbers are. 4th is used because on cars these days 5th gear tend to be a bit of an overdrive.
The throttle is gently floored, and the dyno slowly allows the speed of the engine to increase - this measures the torque of the engine. When the engine reaches maximum RPM, the operator puts the car in neutral, and allows the wheels to decelerate of their own accord - this measures the losses of the transmission,driveshafts,bearings brakes (if they are sticking) and tyres
Now here comes the maths
BHP = Torque (lbft) x RPM
-------------------
5252
This means that BHP is always equal to torque at 5252rpm - if its not then there is something wrong!
Now using a sample we get max power of 169.3BHp @ 7869RPM but 115.0lbft of Torque. The important factor here is that it makes its maximum power at nearly 8000rpm!
The moral of this essay is - it is better to make torque at high RPM for a screamer! - and thats why beause Hondas rev so high they produce the power!
I realise I've forgotten an important part of the calculation
Where did the 5252 figure come from ?
As discussed what we actually measure is torque, expressed in ft/lb, and then we calculate actual horsepower by converting the twisting force of torque into the work units of horsepower.
Visualize a one pound weight, one foot from a fulcrum on an "invisible weightless" bar. If we rotate that weight for one full revolution against a one pound resistance, we have moved it a total of 6.2832 feet (pi times a two foot circle), and, we have done 6.2832 foot pounds of work.
OK. Remember James Watt? He said that 33,000 foot pounds of work per minute was equivalent to one horsepower. If we divide the 6.2832 foot pounds of work we've done per revolution of the weight into 33,000 foot pounds, we come up with the fact that we have to rotate that weight at the rate of 5,252 revolutions per minute in order to do 33,000 foot pounds per minute of work, and thus do work at the equivalent rate of one horsepower.
Therefore, the following formula applies for calculating horsepower from a torque measurement:
Horsepower = ( Torque * RPM ) / 5252
Thats where the 5252 comes from.
Torque is only half the story. While torque is the force created, it doesn't account for the importance of revs.
Imagine trying to remove a wheel nut from a car with a standard wheelbrace and all the torque you could produce can't loosen the "Kwik fit special" airgunned super tightened wheel bolts. You apply lots of force, i.e. torque, but you still can't generate any rpm. Therefore nothing is accomplished, no power generated despite your cursing and kicking. So - Without rpm, torque is useless!
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