VCheng
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I wrote the answers to some interesting questions on Pakwheels several years ago and was just reminiscing:
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https://www.pakwheels.com/forums/t/torque-displacement-or-horsepower/137739/39
VCheng Senior PakWheeler
May '10
hi
Seems like i m stuck with this question for ages now... but havent got an answer... so im dividing my question into a few questions so that its easier for me to understand and you guys to explain... so the experts here r requested to shed sum light over these...
Congratulations on asking the question. Admitting ignorance is the first step towards knowledge. I am no expert but let me try to explain the concepts and your questions without cutting and pasting any links. Once you have understood my anwsers, you will be ready to learn more on the interwebs or elsewhere.
Others may find this post illuminating too. If you still have any questions, please feel free to ask them.
1) what EXACTLY is the difference between torque and horsepower?
Torque is the rotational force produced by the engine and thus by definition is the force capable of doing work. Horsepower is the rate of doing that work. Keep this fact in mind: Torque is the AMOUNT of work an engine can perform, while Horsepower is the speed (i.e. RATE) at which it can do this work.
2) Are they directly proportional to each other? eg if horsepower increases, torque WILL increase?
Torque and Horsepower are related by this equation:
Horsepower = [Torque x rpm] / 5252
This means that below 5252 rpm any engine's torque will always be higher than its horsepower, and above 5252 rpm horsepower will always be higher than its torque. At 5252 rpm both will be exactly the same.
3) what actually the engine produces? torque or hp?
An engine produces Torque. Horsepower is a calculated number. Torque is measured using an engine dynamometer which clamps down on the output shaft using a brake to measure what force is being produced at any given rpm, and then the horsepower is calculated using the formula. That is why the horsepower thus calculated is called the "brake" horsepower or bhp.
4) how does displacement effects both of these?
Displacement is the volume of all the cylinders of an engine. More displacement produces more Torque, whereas the rpm produces more Horsepower. For a given displacement, if the bore is bigger than the stroke, the engine is called an "oversquare" design and if the stroke is bigger than the bore, it is called and "undersquare" design. Oversquare designs have more area that can be used for valves and thus make it easier for the engine to rev higher and produce more Horsepower. Undersquare designs tend to produce more Torque for the same displacement. A larger number of cylinders for the same displacement tends to produce more of both.
5) i ve noticed that if someone modifies a b18 honda engine upto 250hp, and theres another engine lets say XYZ toyota engine with 6 cylinders and stock 250bhp, is this latter engine going to have more torque? if so, that means torque IS directly proportional to displacement.
Yes, Torque is directly proportional to the displacement and Horsepower is directly proportional to the rpm, everything else being equal. If you can burn a larger volume of a fuel/air mixture, you will produce more force. In a naturally aspirated engine, the volume of fuel/air mixture burnt is due to displacement. Forced induction engines will use a turbocharger or a supercharger to force more fuel/air mixture into a given displacment and increase the Torque that way.
6) which of them is more desirable? and in what circustance? eg, for drag races, or hill climbing or offroading etc
Well, personally I like lots and lots of both in a car
. However, it depends on what the engine is required to do. Thus, for a truck, more Torque at a lower rpm is better, but for a race car, more horsepower at high rpm is better. For your scenarios both Torque and Horsepower are important.
7) if u are given a chance to pick up one engine from 2, both are 2000cc, one has 150bhp and 180ft lb of torque , and other one has 150 ft lb of torque but 180bhp which engine will u pick up and for what reasons? ( figures are hypothetical, just to give you guys a scenario)
Using the formula given above, you will see that you also need to look at the rpm at which these engines are making the figures that you have given.
If an engine is making 180 lb-ft of Torque at 2000 rpm, then it is making (180x2000)/5252 = 68.5 bhp at 2000 rpm. If the same engine is making 180 lb-ft of Torque at 4000 rpm, then it is making (180x4000)/5252 = 137 bhp at that 4000 rpm.
Thus, engine specification will give a maximum Torque and Horsepower number as well as the rpm at which those figures are obtained. If you know the Torque or the Horsepower at any given rpm, then you can calculate the other figure for that rpm.
To give an actual example, the Mazda RX-8 engine is rated at 232 bhp @8500 rpm for the manual version and 212 bhp @7500 rpm for the automatic version, with both rated at 159 lb-ft of torque at 5500 rpm. So, if you have two RX-8s, one with an automatic and one with a manual gearbox, both will produce 159 lb-ft of Torque at 5500 rpm and therefore are also making 166.5 hp at 5500 rpm. However, the manual car revs higher, and thus at its rated output of 232 bhp @8500 rpm, it is producing (232x5252)/8500 = 143.4 lb-ft of Torque at 8500 rpm, and the automatic Rx-8 at its rating of 212 bhp @7500 rpm is producing (212x5252)/7500 = 148.5 lb-ft of Torque at 7500 rpm.
8) how is it that a 72bhp engine (2.0D) climbs hills much better then a 1.3L 100bhp city vtec? isnt acceleration just a component of horsepower? if so, why is the 1.3L 100bhp slower in climbing hills?
Now it should be clearer to you. If that 72 bhp engine has a rating of 72 bhp @1500 rpm (like a good 2.0D diesel engine), it is also producing (72x5252)/1500 = 252 lb-ft of Torque at that rpm. So even if you load up the 2.0D, it will go up the hill easily, although slower than the vtec car. The newer vtec car makes 100 bhp at 5500 rpm, it is also making only (100x5252)/5500 = 95 lb-ft of Torque.
The difference will become more apparent when you load up both cars with five people. The low revving, torquey diesel engine will still be able to pull the load up the hill because it is producing more Torque (i.e. the AMOUNT of work it can do it is larger), where the vtec car will bog down. However, with one person on baord, the vtec car will be better at quickly going up the hill (i.e it can do a little AMOUNT of work, but at a much great SPEED or RATE), but the 2.0D car will go up the hill slowly even though it is not loaded (i.e. it will do the work at a slower SPEED or RATE).
Let's take a more extreme example to illustrate my point. Consider a water-wheel used to grind corn. It may produce only 5 bhp, but at only 5 rpm. So it must produce (5x5252)/5 = 5252 lb-ft or Torque, which, by the way, is a whole lot. It may move slowly, but you would not be able to stop it.
Compare that with a model airplane engine. It may produce the same 5 bhp, but at 20,000 rpm. So it is producing only (5x5252)/20000 = 1.3 lb-ft of Torque. So you will be able to stop it easily just by holding the propeller, but it will also be able to take a model airplane, which is very light, into the air at 100 mph.
So the water-wheel has a lot of Torque and the model airplane engine has a lot of Horsepower. Simple, isn't it?
(Acceleration is simply the rate of change of velocity, so I will explain it separately if you still need it since that concept is not directly relevant to this discussion.)
apart from these, kindly use any details to explain me about this...
I have tried to use simple language and given relevant examples. If you still have questions, please let me know.
hope i ll get sum real experts here...
Like I said before, I am not an expert. If there are any spelling or calculation mistakes or any other omissions, please let me know as I am typing this pretty quickly.
thanx n regards...
You are always welcome at PakWheels!
================================
https://www.pakwheels.com/forums/t/torque-displacement-or-horsepower/137739/39
VCheng Senior PakWheeler
May '10
hi
Seems like i m stuck with this question for ages now... but havent got an answer... so im dividing my question into a few questions so that its easier for me to understand and you guys to explain... so the experts here r requested to shed sum light over these...
Congratulations on asking the question. Admitting ignorance is the first step towards knowledge. I am no expert but let me try to explain the concepts and your questions without cutting and pasting any links. Once you have understood my anwsers, you will be ready to learn more on the interwebs or elsewhere.
Others may find this post illuminating too. If you still have any questions, please feel free to ask them.
1) what EXACTLY is the difference between torque and horsepower?
Torque is the rotational force produced by the engine and thus by definition is the force capable of doing work. Horsepower is the rate of doing that work. Keep this fact in mind: Torque is the AMOUNT of work an engine can perform, while Horsepower is the speed (i.e. RATE) at which it can do this work.
2) Are they directly proportional to each other? eg if horsepower increases, torque WILL increase?
Torque and Horsepower are related by this equation:
Horsepower = [Torque x rpm] / 5252
This means that below 5252 rpm any engine's torque will always be higher than its horsepower, and above 5252 rpm horsepower will always be higher than its torque. At 5252 rpm both will be exactly the same.
3) what actually the engine produces? torque or hp?
An engine produces Torque. Horsepower is a calculated number. Torque is measured using an engine dynamometer which clamps down on the output shaft using a brake to measure what force is being produced at any given rpm, and then the horsepower is calculated using the formula. That is why the horsepower thus calculated is called the "brake" horsepower or bhp.
4) how does displacement effects both of these?
Displacement is the volume of all the cylinders of an engine. More displacement produces more Torque, whereas the rpm produces more Horsepower. For a given displacement, if the bore is bigger than the stroke, the engine is called an "oversquare" design and if the stroke is bigger than the bore, it is called and "undersquare" design. Oversquare designs have more area that can be used for valves and thus make it easier for the engine to rev higher and produce more Horsepower. Undersquare designs tend to produce more Torque for the same displacement. A larger number of cylinders for the same displacement tends to produce more of both.
5) i ve noticed that if someone modifies a b18 honda engine upto 250hp, and theres another engine lets say XYZ toyota engine with 6 cylinders and stock 250bhp, is this latter engine going to have more torque? if so, that means torque IS directly proportional to displacement.
Yes, Torque is directly proportional to the displacement and Horsepower is directly proportional to the rpm, everything else being equal. If you can burn a larger volume of a fuel/air mixture, you will produce more force. In a naturally aspirated engine, the volume of fuel/air mixture burnt is due to displacement. Forced induction engines will use a turbocharger or a supercharger to force more fuel/air mixture into a given displacment and increase the Torque that way.
6) which of them is more desirable? and in what circustance? eg, for drag races, or hill climbing or offroading etc
Well, personally I like lots and lots of both in a car
. However, it depends on what the engine is required to do. Thus, for a truck, more Torque at a lower rpm is better, but for a race car, more horsepower at high rpm is better. For your scenarios both Torque and Horsepower are important.7) if u are given a chance to pick up one engine from 2, both are 2000cc, one has 150bhp and 180ft lb of torque , and other one has 150 ft lb of torque but 180bhp which engine will u pick up and for what reasons? ( figures are hypothetical, just to give you guys a scenario)
Using the formula given above, you will see that you also need to look at the rpm at which these engines are making the figures that you have given.
If an engine is making 180 lb-ft of Torque at 2000 rpm, then it is making (180x2000)/5252 = 68.5 bhp at 2000 rpm. If the same engine is making 180 lb-ft of Torque at 4000 rpm, then it is making (180x4000)/5252 = 137 bhp at that 4000 rpm.
Thus, engine specification will give a maximum Torque and Horsepower number as well as the rpm at which those figures are obtained. If you know the Torque or the Horsepower at any given rpm, then you can calculate the other figure for that rpm.
To give an actual example, the Mazda RX-8 engine is rated at 232 bhp @8500 rpm for the manual version and 212 bhp @7500 rpm for the automatic version, with both rated at 159 lb-ft of torque at 5500 rpm. So, if you have two RX-8s, one with an automatic and one with a manual gearbox, both will produce 159 lb-ft of Torque at 5500 rpm and therefore are also making 166.5 hp at 5500 rpm. However, the manual car revs higher, and thus at its rated output of 232 bhp @8500 rpm, it is producing (232x5252)/8500 = 143.4 lb-ft of Torque at 8500 rpm, and the automatic Rx-8 at its rating of 212 bhp @7500 rpm is producing (212x5252)/7500 = 148.5 lb-ft of Torque at 7500 rpm.
8) how is it that a 72bhp engine (2.0D) climbs hills much better then a 1.3L 100bhp city vtec? isnt acceleration just a component of horsepower? if so, why is the 1.3L 100bhp slower in climbing hills?
Now it should be clearer to you. If that 72 bhp engine has a rating of 72 bhp @1500 rpm (like a good 2.0D diesel engine), it is also producing (72x5252)/1500 = 252 lb-ft of Torque at that rpm. So even if you load up the 2.0D, it will go up the hill easily, although slower than the vtec car. The newer vtec car makes 100 bhp at 5500 rpm, it is also making only (100x5252)/5500 = 95 lb-ft of Torque.
The difference will become more apparent when you load up both cars with five people. The low revving, torquey diesel engine will still be able to pull the load up the hill because it is producing more Torque (i.e. the AMOUNT of work it can do it is larger), where the vtec car will bog down. However, with one person on baord, the vtec car will be better at quickly going up the hill (i.e it can do a little AMOUNT of work, but at a much great SPEED or RATE), but the 2.0D car will go up the hill slowly even though it is not loaded (i.e. it will do the work at a slower SPEED or RATE).
Let's take a more extreme example to illustrate my point. Consider a water-wheel used to grind corn. It may produce only 5 bhp, but at only 5 rpm. So it must produce (5x5252)/5 = 5252 lb-ft or Torque, which, by the way, is a whole lot. It may move slowly, but you would not be able to stop it.
Compare that with a model airplane engine. It may produce the same 5 bhp, but at 20,000 rpm. So it is producing only (5x5252)/20000 = 1.3 lb-ft of Torque. So you will be able to stop it easily just by holding the propeller, but it will also be able to take a model airplane, which is very light, into the air at 100 mph.
So the water-wheel has a lot of Torque and the model airplane engine has a lot of Horsepower. Simple, isn't it?
(Acceleration is simply the rate of change of velocity, so I will explain it separately if you still need it since that concept is not directly relevant to this discussion.)
apart from these, kindly use any details to explain me about this...
I have tried to use simple language and given relevant examples. If you still have questions, please let me know.
hope i ll get sum real experts here...
Like I said before, I am not an expert. If there are any spelling or calculation mistakes or any other omissions, please let me know as I am typing this pretty quickly.
thanx n regards...
You are always welcome at PakWheels!
