Torque vs. Horsepower explained by Physics and not Joe Blow dirt track racer.
Mar 10, 2010, 09:52 AM
#18
Wow...
I can't believe some of the responses, especially from well known tuners. Horsepower is not a "unitless number." By definition, it is a "unit" and can be converted directly over to any other power unit.
1 horsepower = 550.000 018 44 foot pound-force/second
Incase anybody is confused, that's the same as Torque [ft-lbf]/time [sec].
The reason HP "matters" and torque "doesn't matter" is that torque has no time reference. All torque says is how "hard" and "far" you can push something, but it doesn't say anything about how long it will take to move that object a given distance.
Put it into perspective. You give me a 20 foot extension and I'll generate 4000 ft-lbs of torque on a wheel. But guess what, for every foot I move in arc length, I'll only rotate that wheel about 3 degrees. How fast do you think I can move? Not very and when the wheel is rotating about 1/20 as much as I'm moving, it becomes quite clear I'm not a very good energy source for a drag car despite the fact that I can generate 4000 ft-lbs of torque.
HP is the ONLY thing that matters. Torque has no reference to time and is therefor, in it's self, useless.
The part where torque matters is at what engine speed that torque happens at because that's what equates to HP.
I can't believe some of the responses, especially from well known tuners. Horsepower is not a "unitless number." By definition, it is a "unit" and can be converted directly over to any other power unit.
1 horsepower = 550.000 018 44 foot pound-force/second
Incase anybody is confused, that's the same as Torque [ft-lbf]/time [sec].
The reason HP "matters" and torque "doesn't matter" is that torque has no time reference. All torque says is how "hard" and "far" you can push something, but it doesn't say anything about how long it will take to move that object a given distance.
Put it into perspective. You give me a 20 foot extension and I'll generate 4000 ft-lbs of torque on a wheel. But guess what, for every foot I move in arc length, I'll only rotate that wheel about 3 degrees. How fast do you think I can move? Not very and when the wheel is rotating about 1/20 as much as I'm moving, it becomes quite clear I'm not a very good energy source for a drag car despite the fact that I can generate 4000 ft-lbs of torque.
HP is the ONLY thing that matters. Torque has no reference to time and is therefor, in it's self, useless.
The part where torque matters is at what engine speed that torque happens at because that's what equates to HP.
Mar 10, 2010, 10:18 AM
#20
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Depends on the dyno.
Dynojets spin a known weight (the rollers) and measure time and acceleration of the roller. These inputs get you horsepower directly, they then back calculate torque. Load bearing dynos like a Mustang or Dynapacks monitor the torque created at the roller directly and then calculate horsepower.
Most engine dynos measure torque at the crank directly and calculate horsepower as well.
Dynojets spin a known weight (the rollers) and measure time and acceleration of the roller. These inputs get you horsepower directly, they then back calculate torque. Load bearing dynos like a Mustang or Dynapacks monitor the torque created at the roller directly and then calculate horsepower.
Most engine dynos measure torque at the crank directly and calculate horsepower as well.
Mar 10, 2010, 10:21 AM
#21
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I've always used the thought of....it takes Torque to set an object in motion and Horsepower to keep it moving.
You cannot move an object by applying horsepower to it. You must apply torque.
You cannot move an object by applying horsepower to it. You must apply torque.
Mar 10, 2010, 10:36 AM
#22
Wow...
I can't believe some of the responses, especially from well known tuners. Horsepower is not a "unitless number." By definition, it is a "unit" and can be converted directly over to any other power unit.
1 horsepower = 550.000 018 44 foot pound-force/second
Incase anybody is confused, that's the same as Torque [ft-lbf]/time [sec].
The reason HP "matters" and torque "doesn't matter" is that torque has no time reference. All torque says is how "hard" and "far" you can push something, but it doesn't say anything about how long it will take to move that object a given distance.
Put it into perspective. You give me a 20 foot extension and I'll generate 4000 ft-lbs of torque on a wheel. But guess what, for every foot I move in arc length, I'll only rotate that wheel about 3 degrees. How fast do you think I can move? Not very and when the wheel is rotating about 1/20 as much as I'm moving, it becomes quite clear I'm not a very good energy source for a drag car despite the fact that I can generate 4000 ft-lbs of torque.
HP is the ONLY thing that matters. Torque has no reference to time and is therefor, in it's self, useless.
The part where torque matters is at what engine speed that torque happens at because that's what equates to HP.
I can't believe some of the responses, especially from well known tuners. Horsepower is not a "unitless number." By definition, it is a "unit" and can be converted directly over to any other power unit.
1 horsepower = 550.000 018 44 foot pound-force/second
Incase anybody is confused, that's the same as Torque [ft-lbf]/time [sec].
The reason HP "matters" and torque "doesn't matter" is that torque has no time reference. All torque says is how "hard" and "far" you can push something, but it doesn't say anything about how long it will take to move that object a given distance.
Put it into perspective. You give me a 20 foot extension and I'll generate 4000 ft-lbs of torque on a wheel. But guess what, for every foot I move in arc length, I'll only rotate that wheel about 3 degrees. How fast do you think I can move? Not very and when the wheel is rotating about 1/20 as much as I'm moving, it becomes quite clear I'm not a very good energy source for a drag car despite the fact that I can generate 4000 ft-lbs of torque.
HP is the ONLY thing that matters. Torque has no reference to time and is therefor, in it's self, useless.
The part where torque matters is at what engine speed that torque happens at because that's what equates to HP.
With this known, in the tuning world.....HP numbers are mute.
Mar 10, 2010, 10:10 PM
#23
I honestly don't get how this argument carries on.
For anybody that thinks torque is responsible for a fast car, that's fine, have fun having an incorrect understanding of basic physics.
If torque was king, we'd all be driving turbo diesels.
Oh, BTW, F1 cars make like 200 ft-lbs of torque but near 900HP and can run a 1/4 in under 10 seconds despite being geared for top end. I guess that 200 ft-lbs is all you need to run 9s, right? Or is it that 900HP that's responsible???
For anybody that thinks torque is responsible for a fast car, that's fine, have fun having an incorrect understanding of basic physics.
If torque was king, we'd all be driving turbo diesels.
Oh, BTW, F1 cars make like 200 ft-lbs of torque but near 900HP and can run a 1/4 in under 10 seconds despite being geared for top end. I guess that 200 ft-lbs is all you need to run 9s, right? Or is it that 900HP that's responsible???
Mar 11, 2010, 04:28 AM
#24
I think the argument carries on because people don't actually think of torque by itself when it comes to cars. They think of torque along with a time component, RPM... which is basically the same idea as horsepower.
So it's six of one, half dozen of the other.
Anyone, can tune any car, from either an HP or a torque curve. It's sort of like using imperial and metric isn't it to some extent? I know if a car is making 500 tq at 9000 rpm it's doing a lot of freakin work because to push that kind of force on something already spinning so fast is hard to do.
So it's six of one, half dozen of the other.
Anyone, can tune any car, from either an HP or a torque curve. It's sort of like using imperial and metric isn't it to some extent? I know if a car is making 500 tq at 9000 rpm it's doing a lot of freakin work because to push that kind of force on something already spinning so fast is hard to do.
Mar 11, 2010, 09:13 AM
#26
I honestly don't get how this argument carries on.
For anybody that thinks torque is responsible for a fast car, that's fine, have fun having an incorrect understanding of basic physics.
If torque was king, we'd all be driving turbo diesels.
Oh, BTW, F1 cars make like 200 ft-lbs of torque but near 900HP and can run a 1/4 in under 10 seconds despite being geared for top end. I guess that 200 ft-lbs is all you need to run 9s, right? Or is it that 900HP that's responsible???
For anybody that thinks torque is responsible for a fast car, that's fine, have fun having an incorrect understanding of basic physics.
If torque was king, we'd all be driving turbo diesels.
Oh, BTW, F1 cars make like 200 ft-lbs of torque but near 900HP and can run a 1/4 in under 10 seconds despite being geared for top end. I guess that 200 ft-lbs is all you need to run 9s, right? Or is it that 900HP that's responsible???
Mar 11, 2010, 09:16 AM
#27
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I honestly don't get how this argument carries on.
For anybody that thinks torque is responsible for a fast car, that's fine, have fun having an incorrect understanding of basic physics.
If torque was king, we'd all be driving turbo diesels.
Oh, BTW, F1 cars make like 200 ft-lbs of torque but near 900HP and can run a 1/4 in under 10 seconds despite being geared for top end. I guess that 200 ft-lbs is all you need to run 9s, right? Or is it that 900HP that's responsible???
For anybody that thinks torque is responsible for a fast car, that's fine, have fun having an incorrect understanding of basic physics.
If torque was king, we'd all be driving turbo diesels.
Oh, BTW, F1 cars make like 200 ft-lbs of torque but near 900HP and can run a 1/4 in under 10 seconds despite being geared for top end. I guess that 200 ft-lbs is all you need to run 9s, right? Or is it that 900HP that's responsible???
i love being devils advocate
so lets say you add 2000lbs to the F1 car to make it street car weight. still think it will run 9's with 200ftlb of torque and 900hp (aside from every component in the transmission getting blown to smithereens)?
now i take a trans-am, slicks, full weight (i.e. heavy pig), give it 600ftlb of torque and a low rev limit (i.e. not a lot of power), and it runs 9's.... so it is the torque or HP getting it to the 9's?
Mar 11, 2010, 09:58 AM
#28
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Also i did not say that horsepower is not important i just stated the fact that Horsepower gives you your top speed, torque gets you moving (accelerating). You could have a million horsepower and one lb ft of torque, you won't be going anywhere fast, you could have 900 lb ft of torque and 1hp you could move a heavy *** object but it won't break any records either. I thought what i said was clear, but i guess not. Horsepower, Torque, Gearing, and Aerodynamics all matter when you're racing!
Mar 11, 2010, 09:58 AM
#29
Actually, that article is very well written and completely accurate, but I think people get confused in the fact that is is comparing a high torque, low RPM engine with a low torque high RPM engine, which are geared differently to achieve the same final top speed.
The F1 car in that configuration will indeed accelerate much faster, but it's due to the gearing differences. Since the F1 car can run to 18000 RPM compared to the 3000RPM of the diesel, it can take advantage of much better gearing to achieve the desired vehicle speed.
If the diesel engine had the ability to actually run to 18000RPM as well, it would be x times as fast where x is the ratio of the torque output of the two motors. So, a 600lb-ft torque motor using the same gearing as a 200 lb-ft torque motor would be 3 times as fast.
But that's not exactly what this paper was trying to describe. It was showing that a high torque motor that can only rev out to a certain RPM needs to be geared in a way where that torque cannot be used for acceleration as well a high HP motor that can rev out to a high RPM. I know it's kind of confusing.
The F1 car in that configuration will indeed accelerate much faster, but it's due to the gearing differences. Since the F1 car can run to 18000 RPM compared to the 3000RPM of the diesel, it can take advantage of much better gearing to achieve the desired vehicle speed.
If the diesel engine had the ability to actually run to 18000RPM as well, it would be x times as fast where x is the ratio of the torque output of the two motors. So, a 600lb-ft torque motor using the same gearing as a 200 lb-ft torque motor would be 3 times as fast.
But that's not exactly what this paper was trying to describe. It was showing that a high torque motor that can only rev out to a certain RPM needs to be geared in a way where that torque cannot be used for acceleration as well a high HP motor that can rev out to a high RPM. I know it's kind of confusing.
Last edited by l2r99gst; Mar 11, 2010 at 10:00 AM.
Mar 11, 2010, 10:11 AM
#30
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I honestly don't get how this argument carries on.
For anybody that thinks torque is responsible for a fast car, that's fine, have fun having an incorrect understanding of basic physics.
If torque was king, we'd all be driving turbo diesels.
Oh, BTW, F1 cars make like 200 ft-lbs of torque but near 900HP and can run a 1/4 in under 10 seconds despite being geared for top end. I guess that 200 ft-lbs is all you need to run 9s, right? Or is it that 900HP that's responsible???
For anybody that thinks torque is responsible for a fast car, that's fine, have fun having an incorrect understanding of basic physics.
If torque was king, we'd all be driving turbo diesels.
Oh, BTW, F1 cars make like 200 ft-lbs of torque but near 900HP and can run a 1/4 in under 10 seconds despite being geared for top end. I guess that 200 ft-lbs is all you need to run 9s, right? Or is it that 900HP that's responsible???
The 900hp isn't what's responsible. It's the 200ft-lbs at 19,000 rpm that's resposible for that tiny engine achieving what it does. Why do you think they idle at 6000-7000 rpm? Not because it sounds cool... Becuase it needs to stay above that to make the power just to keep itself going. Same reason why our cars idle at 850+-50 from the facotry and not like 400-500rpm like a diesel.
Horsepower is Math, torque, rpm and 5252 create it. Period.
Yes it is used to judge approx how fast a car can be. But remember torque and being able to make as much of it, for as much rpm as possible is what's responsible for making something fast.
Think of yourself as torque (physical power) say you can deadlift 200lbs and carry it. Well if you add more torque (another person that can deadlift and carry 200lbs) you suddenly can lift and move the same thing further and faster. How much time it takes you to move that object a set distance is the Horsepower, which had nothing to do with how fast or slow you did it. The torque (number of people helping) did. Same thing in a car. Just with air, gas and controlled (at least most of the time) explosions, instead of the flintstones.