With proper gearing, and sensible disparity, you cannot tell the difference. I owned both an LS1 Trans Am, and a 370Z. Both 6-speed manuals. They had similar hp/weight, but the Trans Am had well over 100# more torque. The cars accelerated the same from any speed it would have been a driver's race. Magazine tests of the two cars tell the same tale. Gearing.
Torque vs Horsepower
- Thread starter DGXR
- Start date
- Status
Originally Posted by KrisZ
If torque by itself is not important, then why is it that most engine designs seek to have the torque curve as flat as possible? Ideally you don't want it to be a curve at all, but rather a nice flat horizontal line.
So true - look at any torque curve of a DC motor, like what is in a Tesla, and then YouTube Tesla vs ... and see who wins most of those races.
If torque by itself is not important, then why is it that most engine designs seek to have the torque curve as flat as possible? Ideally you don't want it to be a curve at all, but rather a nice flat horizontal line.
So true - look at any torque curve of a DC motor, like what is in a Tesla, and then YouTube Tesla vs ... and see who wins most of those races.
Originally Posted by madRiver
I love modern day 4cyl DI turbos because you get max torque(221 ft-lbs my Tiguan ) at 1500rpm -4500 typically so everyday driving is a pleasure.
This.
I love modern day 4cyl DI turbos because you get max torque(221 ft-lbs my Tiguan ) at 1500rpm -4500 typically so everyday driving is a pleasure.
This.
Originally Posted by 4WD
Originally Posted by Anduril
Originally Posted by DukeOfFrontenac
Not sure where I read it - 'Horsepower is how fast you hit the wall, torque is how far you take the wall with you'.
That would be momentum
Mass x velocity = Force. Once at speed I could cut the engine off before hitting the wall …
More like torque x RPM / constant
Nope...F=ma, not mv.
Momentum=mv (very helpful for ideal collisions).
Kinetic energy=mv**2.
Analyzing a car hitting a wall is likely going to involve the plastic properties of the vehicle components more than anything else...
Originally Posted by Anduril
Originally Posted by DukeOfFrontenac
Not sure where I read it - 'Horsepower is how fast you hit the wall, torque is how far you take the wall with you'.
That would be momentum
Mass x velocity = Force. Once at speed I could cut the engine off before hitting the wall …
More like torque x RPM / constant
Nope...F=ma, not mv.
Momentum=mv (very helpful for ideal collisions).
Kinetic energy=mv**2.
Analyzing a car hitting a wall is likely going to involve the plastic properties of the vehicle components more than anything else...
dnewton3
Staff member
RayCJ and AHarman and a few others have this right, but we need to be careful in how we use certain terms. We have to agree on some fundamental concepts of definitions.
First, we have to understand that there is a word we all use that really needs to be further defined and more accurately applied. The word is "distance". Distance is a measurement of linearity and nothing more. However, displacement is the measurement of moving an item over that distance. We get lazy and use the term "distance" when we really mean "displacement". Distance is the difference in location of two points. Displacement is moving from one point to the other point. But we say "distance" often referring to either concept, and that starts the first misunderstanding when we get deeper into the concept of work and torque.
Force = mass x acceleration. Force applied over a displacement is called "work". It's a product; force x displacement. I am perfectly fine with folks saying "work is force x distance"; I get the concept they are conveying. But it becomes a problem once we describe the next concept to be discussed ...
Torque is a unique concept because it is a rotational force product, and can be static or dynamic. You can produce torque by pushing down on a lever, and nothing moves (example: you push on the ratchet tool but the bolt does not turn). You are creating torque, but not enough torque to break the bolt loose. OR ... torque can be in motion. A typical electric motor will make constant torque at speed. In fact, that same electric motor will make the same torque at rest (though energized) or at speed. Some people call torque "work" because it's still a force x distance concept, but it's not distance traveled (displacement), rather it's application of force at a specific distance. And I want to clarify one thing here that is PARAMOUNT. Torque is not "a force". That is impossible to reconcile in math. You cannot state that Torque = force x distance if you also state that Torque is a "force". (if Torque stated as T is a "force", then you'd create an irreconcilable equation of "F = F x D". You cannot make the UoM (units of measurement) work out of you state that "Torque is a force". The word "is" means "equal" in math. You cannot state Torque is force because it would mean that torque (improperly stated as a "force") is = force x distance. You cannot say "pounds = pounds x feet"; it's in irreconcilable statement. What you need to understand is that Torque is a "Force Product"; T = F x D. Again, we get lazy and say Torque is a "force", but it's not; it's a product of torque and some distance. "Product" is the proper term of the result of mathematical multiplication. Torque is a force product, not a force.
Some folks get confused when they think of "force" relative to acceleration. This is because they misunderstand that acceleration means something is moving. THAT IS NOT ALWAYS TRUE. Acceleration is the concept of a change in velocity applied over time, and not "moving". Think I am wrong? Consider that everything you have around you is subject to the acceleration of gravity. That coffee mug sitting next to your computer, and the coffee in it, are subject to the acceleration via the mass of earth. If this were not true, then the mug and the coffee would be free floating in space. Just because the coffee is not moving, does not mean that it is not being accelerated. Quit thinking of acceleration in terms of movement, and then it all becomes much more understandable. Hence, the coffee/mug apply a force upon the table; we use the term "weight" (units of pounds for my example for we US based folks). A person lying on the couch is applying a force downward, and the couch is countering with a force upward. They are in equilibrium. Once one overcomes the other, true displacement takes place. Once you get this, you can then understand "torque" (force x distance) because force = mass x acceleration. Torque, as I said, can be either moving or not moving; does not matter. This is because the force is applied at a distance, not over a displacement. It's really seen as this ... Torque = mass x acceleration x distance. The reason torque can either be moving or not moving is because acceleration is independent of displacement. Force only means movement if the application of force overcomes the resistance of force. Torque only means movement if the torque of movement overcomes the torque of resistance.
Nothing moves without force. Nothing. Force has to be applied for something to move. Whether in rotation or linear displacement, nothing moves without force applied.
Unfortunately, people confuse the concepts of torque and force and work because of the misuse of the words distance versus displacement.
Work is force x displacement; we are moving something
Torque is force x distance; we are applying a lever arm in a rotational manner
We would measure both displacement and distance in "feet", but it's done in different manners. Work is measured when something moves. Torque is measured when something is being twisted. But the units of measure are the same (ft and lbs in this common example). That is KEY to getting the rest of the conversation correct.
All that now said, we turn to the whole HP and Torque debate ...
As I said just a moment ago, nothing moves without force. And nothing stops without force. The whole topic of "torque is for towing and HP is for racing" is a total maligning of understanding of the topics. Again, for the third time, NOTHING MOVES OR STOPS WITHOUT FORCE. The question becomes, how is that force generated and applied? HP is only a statement of torque at a certain RPM. Again, a few others have already adequately described the equation of HP from Torque. "Horsepower" is just an arbitrary word; it could just as easily be called "pickle power" or "paper weight power". HP is a concept of Torque at a stated RPM. Unfortunately, once again our lazy nature means we don't often fully describe HP. If OEMs were more specific, they would state "Our awesome new engine produces a maximum 300HP at 5800 rpm". From that accurate statement, you could then understand the torque available, but it would only apply at that specific rpm. VERY IMPORTANT CONCEPT HERE ... "horsepower" is a misnomer. "Power" is simply defined as work per unit of time. In math it would look like this ...
Power = work / time
Power = (force x displacement) / time
Power = (mass x acceleration x displacement) / time.
And that is where the whole "rpm" thing comes into play, because it introduces the concept of time. "Horsepower" is merely a statement of torque at a specific rpm, where rpm is a complex expression of a rotational distance covered for some duration of time.
So, what does it take to move a vehicle? Force. Not "horsepower" or "torque", but Force!
Let's be simple; let's only think of a level surface (road) and a typical car. To move forward, it has to overcome it's mass inertia of sitting still and that of rolling resistance of the tires, and frictional resistance, etc; each of those is a resistant force. We will combine all that resistance into one statement; I'll pick an arbitrary value and say it's going to take 200 lbs of force to initiate movement forward. That 200 lb of force needed to move and overcome the resistance force comes from a complex process of converting hydrocarbon energy to linear movement. We'll ignore the combustion process and focus on the drive train. The engine product (the output) is torque. Torque must now be converted mechanically from a rotational force-product to linear movement.
We'll assume the engine makes 25 ft-lb of torque at idle
We'll assume that the automatic tranny at engine idle gives us a torque-converter advantage of 2:1.
We'll assume first gear is a ration of 3:1.
We'll assume the rear diff is 3:1.
We'll assume the tire diameter is 24 inches, so the radius is 12 inches (ignoring tire compression for you purists) (I chose this because 12 in = 1 foot; easy for the following math below) (the radius of the tire is the distance of the torque arm)
If the engine makes 25 fl-lb of torque at idle, how much "force" is able to be applied by the drive-train at the road surface? (we'll call this the available drive-train force)
F = (engine torque x converter multiplier x first gear multiplier x diff multiplier) / torque arm distance
F = (25 ft-lb x 2 x 3 x 3) / 1 ft
F = (25 x 2 x 3 x 3) / 1 { note that the ft in "ft-lb" in the numerator cancels the ft in the denominator, and so the result is only "lb"; convenient, because our UoM is "pounds" of force}
The drive-train is providing 450 lbs of force; it can easily overcome the resistance force of 200 lb, and so the car moves forward.
You see, NOTHING MOVES OR STOPS WITHOUT FORCE. "Horsepower" is just an arbitrary word to describe a valuation of torque at some specific rpm, where rpm describes the complex math of rotational distance per unit of time.
An engine that makes 200 ft-lb at 1000 rpm generates the same output ("horsepower") as another engine that makes 100 ft-lb at 2000 rpm. That's because (200 x 1000) / 5252 is the same as (100 x 2000) / 5252. They both make 38 "horsepower".
An engine that makes 200-fl-lb at 1000 rpm generates half the output as another engine that makes 200 ft-lb at 2000 rpm. 38HP versus 76HP. (work per unit of time means the engine that does the same work in half the time is twice as "powerful").
However, what wins any race or any towing contest is Force, because it takes force to overcome force. How the force is multiplied is a matter of mechanical leverage. In fact, force starts in the engine as a linear concept; the piston travels in a straight bore. Then the crank converts the linear movement into rotational movement, which is carried throughout the drive-train until it reaches the rear wheel, where the movement is changed back from rotation (turning of the wheel) to linear (tire circumference at road surface).
"Horsepower" does not win races; Force wins races. Torque does not pull an RV uphill; Force moves loads uphill. And Force stops things. How force is generated and converted is just a matter of application unique to the situation. It can be a hydrocarbon fueled engine, an electric motor, or even a matter of hydraulic pressure (pressure being a force applied to an area).
Thus endeth the lesson.
First, we have to understand that there is a word we all use that really needs to be further defined and more accurately applied. The word is "distance". Distance is a measurement of linearity and nothing more. However, displacement is the measurement of moving an item over that distance. We get lazy and use the term "distance" when we really mean "displacement". Distance is the difference in location of two points. Displacement is moving from one point to the other point. But we say "distance" often referring to either concept, and that starts the first misunderstanding when we get deeper into the concept of work and torque.
Force = mass x acceleration. Force applied over a displacement is called "work". It's a product; force x displacement. I am perfectly fine with folks saying "work is force x distance"; I get the concept they are conveying. But it becomes a problem once we describe the next concept to be discussed ...
Torque is a unique concept because it is a rotational force product, and can be static or dynamic. You can produce torque by pushing down on a lever, and nothing moves (example: you push on the ratchet tool but the bolt does not turn). You are creating torque, but not enough torque to break the bolt loose. OR ... torque can be in motion. A typical electric motor will make constant torque at speed. In fact, that same electric motor will make the same torque at rest (though energized) or at speed. Some people call torque "work" because it's still a force x distance concept, but it's not distance traveled (displacement), rather it's application of force at a specific distance. And I want to clarify one thing here that is PARAMOUNT. Torque is not "a force". That is impossible to reconcile in math. You cannot state that Torque = force x distance if you also state that Torque is a "force". (if Torque stated as T is a "force", then you'd create an irreconcilable equation of "F = F x D". You cannot make the UoM (units of measurement) work out of you state that "Torque is a force". The word "is" means "equal" in math. You cannot state Torque is force because it would mean that torque (improperly stated as a "force") is = force x distance. You cannot say "pounds = pounds x feet"; it's in irreconcilable statement. What you need to understand is that Torque is a "Force Product"; T = F x D. Again, we get lazy and say Torque is a "force", but it's not; it's a product of torque and some distance. "Product" is the proper term of the result of mathematical multiplication. Torque is a force product, not a force.
Some folks get confused when they think of "force" relative to acceleration. This is because they misunderstand that acceleration means something is moving. THAT IS NOT ALWAYS TRUE. Acceleration is the concept of a change in velocity applied over time, and not "moving". Think I am wrong? Consider that everything you have around you is subject to the acceleration of gravity. That coffee mug sitting next to your computer, and the coffee in it, are subject to the acceleration via the mass of earth. If this were not true, then the mug and the coffee would be free floating in space. Just because the coffee is not moving, does not mean that it is not being accelerated. Quit thinking of acceleration in terms of movement, and then it all becomes much more understandable. Hence, the coffee/mug apply a force upon the table; we use the term "weight" (units of pounds for my example for we US based folks). A person lying on the couch is applying a force downward, and the couch is countering with a force upward. They are in equilibrium. Once one overcomes the other, true displacement takes place. Once you get this, you can then understand "torque" (force x distance) because force = mass x acceleration. Torque, as I said, can be either moving or not moving; does not matter. This is because the force is applied at a distance, not over a displacement. It's really seen as this ... Torque = mass x acceleration x distance. The reason torque can either be moving or not moving is because acceleration is independent of displacement. Force only means movement if the application of force overcomes the resistance of force. Torque only means movement if the torque of movement overcomes the torque of resistance.
Nothing moves without force. Nothing. Force has to be applied for something to move. Whether in rotation or linear displacement, nothing moves without force applied.
Unfortunately, people confuse the concepts of torque and force and work because of the misuse of the words distance versus displacement.
Work is force x displacement; we are moving something
Torque is force x distance; we are applying a lever arm in a rotational manner
We would measure both displacement and distance in "feet", but it's done in different manners. Work is measured when something moves. Torque is measured when something is being twisted. But the units of measure are the same (ft and lbs in this common example). That is KEY to getting the rest of the conversation correct.
All that now said, we turn to the whole HP and Torque debate ...
As I said just a moment ago, nothing moves without force. And nothing stops without force. The whole topic of "torque is for towing and HP is for racing" is a total maligning of understanding of the topics. Again, for the third time, NOTHING MOVES OR STOPS WITHOUT FORCE. The question becomes, how is that force generated and applied? HP is only a statement of torque at a certain RPM. Again, a few others have already adequately described the equation of HP from Torque. "Horsepower" is just an arbitrary word; it could just as easily be called "pickle power" or "paper weight power". HP is a concept of Torque at a stated RPM. Unfortunately, once again our lazy nature means we don't often fully describe HP. If OEMs were more specific, they would state "Our awesome new engine produces a maximum 300HP at 5800 rpm". From that accurate statement, you could then understand the torque available, but it would only apply at that specific rpm. VERY IMPORTANT CONCEPT HERE ... "horsepower" is a misnomer. "Power" is simply defined as work per unit of time. In math it would look like this ...
Power = work / time
Power = (force x displacement) / time
Power = (mass x acceleration x displacement) / time.
And that is where the whole "rpm" thing comes into play, because it introduces the concept of time. "Horsepower" is merely a statement of torque at a specific rpm, where rpm is a complex expression of a rotational distance covered for some duration of time.
So, what does it take to move a vehicle? Force. Not "horsepower" or "torque", but Force!
Let's be simple; let's only think of a level surface (road) and a typical car. To move forward, it has to overcome it's mass inertia of sitting still and that of rolling resistance of the tires, and frictional resistance, etc; each of those is a resistant force. We will combine all that resistance into one statement; I'll pick an arbitrary value and say it's going to take 200 lbs of force to initiate movement forward. That 200 lb of force needed to move and overcome the resistance force comes from a complex process of converting hydrocarbon energy to linear movement. We'll ignore the combustion process and focus on the drive train. The engine product (the output) is torque. Torque must now be converted mechanically from a rotational force-product to linear movement.
We'll assume the engine makes 25 ft-lb of torque at idle
We'll assume that the automatic tranny at engine idle gives us a torque-converter advantage of 2:1.
We'll assume first gear is a ration of 3:1.
We'll assume the rear diff is 3:1.
We'll assume the tire diameter is 24 inches, so the radius is 12 inches (ignoring tire compression for you purists) (I chose this because 12 in = 1 foot; easy for the following math below) (the radius of the tire is the distance of the torque arm)
If the engine makes 25 fl-lb of torque at idle, how much "force" is able to be applied by the drive-train at the road surface? (we'll call this the available drive-train force)
F = (engine torque x converter multiplier x first gear multiplier x diff multiplier) / torque arm distance
F = (25 ft-lb x 2 x 3 x 3) / 1 ft
F = (25 x 2 x 3 x 3) / 1 { note that the ft in "ft-lb" in the numerator cancels the ft in the denominator, and so the result is only "lb"; convenient, because our UoM is "pounds" of force}
The drive-train is providing 450 lbs of force; it can easily overcome the resistance force of 200 lb, and so the car moves forward.
You see, NOTHING MOVES OR STOPS WITHOUT FORCE. "Horsepower" is just an arbitrary word to describe a valuation of torque at some specific rpm, where rpm describes the complex math of rotational distance per unit of time.
An engine that makes 200 ft-lb at 1000 rpm generates the same output ("horsepower") as another engine that makes 100 ft-lb at 2000 rpm. That's because (200 x 1000) / 5252 is the same as (100 x 2000) / 5252. They both make 38 "horsepower".
An engine that makes 200-fl-lb at 1000 rpm generates half the output as another engine that makes 200 ft-lb at 2000 rpm. 38HP versus 76HP. (work per unit of time means the engine that does the same work in half the time is twice as "powerful").
However, what wins any race or any towing contest is Force, because it takes force to overcome force. How the force is multiplied is a matter of mechanical leverage. In fact, force starts in the engine as a linear concept; the piston travels in a straight bore. Then the crank converts the linear movement into rotational movement, which is carried throughout the drive-train until it reaches the rear wheel, where the movement is changed back from rotation (turning of the wheel) to linear (tire circumference at road surface).
"Horsepower" does not win races; Force wins races. Torque does not pull an RV uphill; Force moves loads uphill. And Force stops things. How force is generated and converted is just a matter of application unique to the situation. It can be a hydrocarbon fueled engine, an electric motor, or even a matter of hydraulic pressure (pressure being a force applied to an area).
Thus endeth the lesson.
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Torque is the only thing that accelerates the car on flat ground. More torque means faster acceleration. Horsepower determines how fast you go. More horsepower equals higher max speed.
A diesel BMW has more torque and accelerates faster than when equipped with a comparable gas engine. Diesel has less hp and therefore lower top speed.
A diesel BMW has more torque and accelerates faster than when equipped with a comparable gas engine. Diesel has less hp and therefore lower top speed.
Horse power is is peak power torque is how fast you get there
Originally Posted by RayCJ
Originally Posted by A_Harman
Originally Posted by RayCJ
Originally Posted by DGXR
I understand what each means but I don't understand the mathematical equation that all the engineers use:
HP = (TQ x RPM)/5252
How could this equation be true for every engine? There are SO MANY different engine designs: different bore x stroke, different compression ratios, 2 large valves vs 4 small valves per cylinder, different camshaft profiles... all these factors will affect the output of torque vs HP at different RPMs and different throttle settings. Specifically I am thinking of the long-stroke Harley-Davidson motorcycle engines that produce loads of torque off-idle vs an equivalent displacement Honda 4-cylinder motorcycle engine that produces comparatively little torque off idle but way more peak HP than the Harley. In this scenario the Harley has high TQ at low RPM, which would generally equal a high HP number. And the Honda has a low TQ at a low RPM, which would generally equal a low HP number but the Honda ultimately produces more peak HP. So again it does not make sense to me.
What am I missing here? Someone please explain, preferably in the simplest terms possible.
Thank you!
In the simplest terms without using much math...
A long time ago, folks settled on the idea that a horse could pull a rope connected to a pulley and lift a 550 lb weight at constant rate of 1 foot per second. Since there's 60 seconds per minute, that converts to an equivalent of 33,000 pounds per minute because 550 x 60 = 33,000. This calculation is for things moving in a straight line. Engines have shafts that rotate so, conversions must be done to convert linear speed to rotational speed. The circumference of a round shaft is 2 x Pi x radius (Pi = 3.1416).
When all is said and done, the 5252 comes from 2 x Pi / 33,000 (because 2 x 3.1416 / 33,000 is roughly equal to 5252). Think of it as a conversion factor from linear motion per second to rotational motion per minute.
Thus: Horsepower ends-up equaling (Torque x RPM) / 5252.
Taking it a little further, Torque = Force x Distance. ( Example: Think of a 1 foot long wrench with 5 lbs of weight at the end. The torque will be 5 ft lbs).
Horsepower is the rate at which you can apply torque and is: (Force x Distance) / Time.
In other words, Horsepower = Torque / Time.
Your train of logic goes off the rails when you get here. You are equating torque to work done, and that is incorrect. To convert torque to work done, multiply torque by 2*pi. For example, if an engine is producing 100 lb*ft torque, and rotates through 2 revolutions, then it has done 100 lb*ft x 2 revolutions x (2*pi) radians/revolution = 1256 lb*ft of work
The definition of Horsepower was originated by James Watt when he was developing steam engines to pump water out of coal mines in England. He put a scale on a horse pushing a capstan on a pump and measured 181 pounds of force while covering 180 feet per minute. Multiplying, the work done per unit time was 32,580 lb*ft/min, which Watt rounded up to 33000, and called a Horsepower. The creators of the Metric system honored James Watt by naming its unit of power the Watt, which is a Newton*meter / second.
I guess it depends on which history book you want to believe. Watt had a very hard time selling the notion of horsepower and it's quite possible there are different explanations of why it came about. In your example, you've gone from arbitrary revolutions to radians. In my example I'm showing that the constant 5252 is the rounded value of (33,000 ftâ‹…lbf/min)/(2Ï€ rad/rev) but I'm not showing the details of conversion because most folks have a hard time understanding radians (as evidenced by the countless freshmen and sophomore college kids I taught this class to).
https://en.wikipedia.org/wiki/Horsepower
Horsepower (hp) is a unit of measurement of power, or the rate at which work is done. There are many different standards and types of horsepower. Two common definitions being used today are the mechanical horsepower (or imperial horsepower), which is about 745.7 watts, and the metric horsepower, which is approximately 735.5 watts.
The term was adopted in the late 18th century by Scottish engineer James Watt to compare the output of steam engines with the power of draft horses. It was later expanded to include the output power of other types of piston engines, as well as turbines, electric motors and other machinery.[1][2] The definition of the unit varied among geographical regions. Most countries now use the SI unit watt for measurement of power. With the implementation of the EU Directive 80/181/EEC on January 1, 2010, the use of horsepower in the EU is permitted only as a supplementary unit.[3]
When I was struggling to understand the concept of "Horsepower", the key was understanding that 33000 ft*lb/min was a number that was defined to quantify how much work a horse could do in a given amount of time. When I was first reading about it in Hot Rod magazine, I kept wondering "Where is this 33000 number coming from?" Hearing the story of how James Watt arrived at that value really drove home the concept to me.
Originally Posted by A_Harman
Originally Posted by RayCJ
Originally Posted by DGXR
I understand what each means but I don't understand the mathematical equation that all the engineers use:
HP = (TQ x RPM)/5252
How could this equation be true for every engine? There are SO MANY different engine designs: different bore x stroke, different compression ratios, 2 large valves vs 4 small valves per cylinder, different camshaft profiles... all these factors will affect the output of torque vs HP at different RPMs and different throttle settings. Specifically I am thinking of the long-stroke Harley-Davidson motorcycle engines that produce loads of torque off-idle vs an equivalent displacement Honda 4-cylinder motorcycle engine that produces comparatively little torque off idle but way more peak HP than the Harley. In this scenario the Harley has high TQ at low RPM, which would generally equal a high HP number. And the Honda has a low TQ at a low RPM, which would generally equal a low HP number but the Honda ultimately produces more peak HP. So again it does not make sense to me.
What am I missing here? Someone please explain, preferably in the simplest terms possible.
Thank you!
In the simplest terms without using much math...
A long time ago, folks settled on the idea that a horse could pull a rope connected to a pulley and lift a 550 lb weight at constant rate of 1 foot per second. Since there's 60 seconds per minute, that converts to an equivalent of 33,000 pounds per minute because 550 x 60 = 33,000. This calculation is for things moving in a straight line. Engines have shafts that rotate so, conversions must be done to convert linear speed to rotational speed. The circumference of a round shaft is 2 x Pi x radius (Pi = 3.1416).
When all is said and done, the 5252 comes from 2 x Pi / 33,000 (because 2 x 3.1416 / 33,000 is roughly equal to 5252). Think of it as a conversion factor from linear motion per second to rotational motion per minute.
Thus: Horsepower ends-up equaling (Torque x RPM) / 5252.
Taking it a little further, Torque = Force x Distance. ( Example: Think of a 1 foot long wrench with 5 lbs of weight at the end. The torque will be 5 ft lbs).
Horsepower is the rate at which you can apply torque and is: (Force x Distance) / Time.
In other words, Horsepower = Torque / Time.
Your train of logic goes off the rails when you get here. You are equating torque to work done, and that is incorrect. To convert torque to work done, multiply torque by 2*pi. For example, if an engine is producing 100 lb*ft torque, and rotates through 2 revolutions, then it has done 100 lb*ft x 2 revolutions x (2*pi) radians/revolution = 1256 lb*ft of work
The definition of Horsepower was originated by James Watt when he was developing steam engines to pump water out of coal mines in England. He put a scale on a horse pushing a capstan on a pump and measured 181 pounds of force while covering 180 feet per minute. Multiplying, the work done per unit time was 32,580 lb*ft/min, which Watt rounded up to 33000, and called a Horsepower. The creators of the Metric system honored James Watt by naming its unit of power the Watt, which is a Newton*meter / second.
I guess it depends on which history book you want to believe. Watt had a very hard time selling the notion of horsepower and it's quite possible there are different explanations of why it came about. In your example, you've gone from arbitrary revolutions to radians. In my example I'm showing that the constant 5252 is the rounded value of (33,000 ftâ‹…lbf/min)/(2Ï€ rad/rev) but I'm not showing the details of conversion because most folks have a hard time understanding radians (as evidenced by the countless freshmen and sophomore college kids I taught this class to).
https://en.wikipedia.org/wiki/Horsepower
Horsepower (hp) is a unit of measurement of power, or the rate at which work is done. There are many different standards and types of horsepower. Two common definitions being used today are the mechanical horsepower (or imperial horsepower), which is about 745.7 watts, and the metric horsepower, which is approximately 735.5 watts.
The term was adopted in the late 18th century by Scottish engineer James Watt to compare the output of steam engines with the power of draft horses. It was later expanded to include the output power of other types of piston engines, as well as turbines, electric motors and other machinery.[1][2] The definition of the unit varied among geographical regions. Most countries now use the SI unit watt for measurement of power. With the implementation of the EU Directive 80/181/EEC on January 1, 2010, the use of horsepower in the EU is permitted only as a supplementary unit.[3]
When I was struggling to understand the concept of "Horsepower", the key was understanding that 33000 ft*lb/min was a number that was defined to quantify how much work a horse could do in a given amount of time. When I was first reading about it in Hot Rod magazine, I kept wondering "Where is this 33000 number coming from?" Hearing the story of how James Watt arrived at that value really drove home the concept to me.
A car really only needs enough torque to spin the wheels. HP determines how fast the wheels spin. You could theoretically put a Briggs and Stratton lawn mower engine in a fully-loaded 18-wheeler, and with some absolutely ridiculous amount of gear-reduction, it will have enough TORQUE to get the wheels moving and move the whole rig down the road. It'll be SUPER slow; your speed would be measured in feet per hour or inches per hour instead of miles per hour, but it'll move. If the engine can't make the wheels move at all, then you don't have enough torque. You'll need either an engine with more torque, or more gear reduction to multiply the torque the engine has. But once you have enough torque to get the wheels moving, more torque isn't going to help you in any way. If you want it to move faster, you'll need more HORSEPOWER. If you wanted the truck to move one mile down the road, you can either do it with a Briggs and Stratton, or a big Cummins. Both will move the truck from Point A to Point B, accomplishing the same amount of WORK. The Briggs will get the truck to Point B...eventually....and the Cummins will get the truck there much, MUCH faster. Again, it's the SAME amount of work. HP is the ability to do a given amount of work over time. More HP = ability to get work done in a shorter amount of time.
Basically - Cummins engine: puts out a certain amount of torque at a certain RPM, let's say at idle ~700 RPM. You can calculate the amount of HP it has at this RPM based on the amount of torque it puts out.
Briggs and Stratton + tons of gear-reduction: puts out the SAME amount of torque as the Cummins, but it's not gonna be anywhere near as fast as 700 RPM, even with the engine running wide-open. The output shaft of the transmission will be turning super slow, and as a result, anything attached to that output shaft will be turning super slow. Therefore, even though the amount of torque is the same, it will have much less HP.
Basically - Cummins engine: puts out a certain amount of torque at a certain RPM, let's say at idle ~700 RPM. You can calculate the amount of HP it has at this RPM based on the amount of torque it puts out.
Briggs and Stratton + tons of gear-reduction: puts out the SAME amount of torque as the Cummins, but it's not gonna be anywhere near as fast as 700 RPM, even with the engine running wide-open. The output shaft of the transmission will be turning super slow, and as a result, anything attached to that output shaft will be turning super slow. Therefore, even though the amount of torque is the same, it will have much less HP.
Originally Posted by walterjay
So do I want a car with a lot of torque or a lot of horsepower? Never could figure that out.
No, you want a safe, reliable, and comfortable car with good fuel economy. Hope that helps.
So do I want a car with a lot of torque or a lot of horsepower? Never could figure that out.
No, you want a safe, reliable, and comfortable car with good fuel economy. Hope that helps.
Originally Posted by brages
Originally Posted by walterjay
So do I want a car with a lot of torque or a lot of horsepower? Never could figure that out.
No, you want a safe, reliable, and comfortable car with good fuel economy. Hope that helps.
300hp and 30mpg highway is perfect
Originally Posted by walterjay
So do I want a car with a lot of torque or a lot of horsepower? Never could figure that out.
No, you want a safe, reliable, and comfortable car with good fuel economy. Hope that helps.
300hp and 30mpg highway is perfect
Originally Posted by Skippy722
Originally Posted by brages
Originally Posted by walterjay
So do I want a car with a lot of torque or a lot of horsepower? Never could figure that out.
No, you want a safe, reliable, and comfortable car with good fuel economy. Hope that helps.
300hp and 30mpg highway is perfect
For now, but in the 70's? That would have been INSANE! In 2030? It will be crap.
It's amazing how we as a species can advance an explosion-powered air pump!
Originally Posted by brages
Originally Posted by walterjay
So do I want a car with a lot of torque or a lot of horsepower? Never could figure that out.
No, you want a safe, reliable, and comfortable car with good fuel economy. Hope that helps.
300hp and 30mpg highway is perfect
For now, but in the 70's? That would have been INSANE! In 2030? It will be crap.
It's amazing how we as a species can advance an explosion-powered air pump!
Originally Posted by 4WD
Mass x velocity = Force.
You need to differentiate that velocity one more time, so you have F=ma.
What you have there is momentum.
Of course, Imperial/U.S. units give me a headache! SI makes things much easier. I don't even like using derived units. Use SI, carry through dimensional analysis, and you'll stay on the rails much more easily.
Mass x velocity = Force.
You need to differentiate that velocity one more time, so you have F=ma.
Of course, Imperial/U.S. units give me a headache! SI makes things much easier. I don't even like using derived units. Use SI, carry through dimensional analysis, and you'll stay on the rails much more easily.
4WD
$50 site donor 2024
Ok, how force is related to momentum in the general driveline question - the example I replied to was hitting a wall - impact force.
Guess people were also going back in forth over the F150 example - momentum or inertia … Either way tends to stay in motion (until).
Guess people were also going back in forth over the F150 example - momentum or inertia … Either way tends to stay in motion (until).
Consider this if you will, in 1959 Oldsmobile had a V8 that developed max torque at a higher RPM than max horsepower. Both figures at around 2,000 RPM if memory serves.
Originally Posted by Dinoburner
... in 1959 Oldsmobile had a V8 that developed max torque at a higher RPM than max horsepower. Both figures at around 2,000 RPM if memory serves.
Impossible. Maybe you looked at a specification chart with a typo?
... in 1959 Oldsmobile had a V8 that developed max torque at a higher RPM than max horsepower. Both figures at around 2,000 RPM if memory serves.
Impossible. Maybe you looked at a specification chart with a typo?
Originally Posted by DGXR
I understand what each means but I don't understand the mathematical equation that all the engineers use:
HP = (TQ x RPM)/5252
How could this equation be true for every engine!
The equation defines mechanical power. It would be the same equation if it was a guy pedalling a bicycle down the road.
Go read up on how Mr. Watt came up with the equation.
I understand what each means but I don't understand the mathematical equation that all the engineers use:
HP = (TQ x RPM)/5252
How could this equation be true for every engine!
The equation defines mechanical power. It would be the same equation if it was a guy pedalling a bicycle down the road.
Go read up on how Mr. Watt came up with the equation.
Originally Posted by A_Harman
People are always asking "do you want torque or horsepower in your engine?"
That is an invalid question. The two represent different physical quantities.
Torque is twisting force.
Power is the rate at which work is done.
You can't have one without the other.
An engine can't make any power unless it makes torque.
Yep, and it also can't make power if there is no rotational movement/RPM.
You can put static torque on a lever like a torque wrench, but if it's not moving it's not producing any power.
People are always asking "do you want torque or horsepower in your engine?"
That is an invalid question. The two represent different physical quantities.
Torque is twisting force.
Power is the rate at which work is done.
You can't have one without the other.
An engine can't make any power unless it makes torque.
Yep, and it also can't make power if there is no rotational movement/RPM.
You can put static torque on a lever like a torque wrench, but if it's not moving it's not producing any power.
Originally Posted by KrisZ
If torque by itself is not important, then why is it that most engine designs seek to have the torque curve as flat as possible? Ideally you don't want it to be a curve at all, but rather a nice flat horizontal line.
Because a flat torque curve will result in a nice linearly increasing HP curve. Flat torque curves are achieved by making the engine volumetric efficiency (VE) as high and as constant as possible over the RPM range.
If torque by itself is not important, then why is it that most engine designs seek to have the torque curve as flat as possible? Ideally you don't want it to be a curve at all, but rather a nice flat horizontal line.
Because a flat torque curve will result in a nice linearly increasing HP curve. Flat torque curves are achieved by making the engine volumetric efficiency (VE) as high and as constant as possible over the RPM range.
Originally Posted by ZeeOSix
Originally Posted by KrisZ
If torque by itself is not important, then why is it that most engine designs seek to have the torque curve as flat as possible? Ideally you don't want it to be a curve at all, but rather a nice flat horizontal line.
Because a flat torque curve will result in a nice linearly increasing HP curve. Flat torque curves are achieved by making the engine volumetric efficiency (VE) as high and as constant as possible over the RPM range.
Yes, that's correct. I posed the question to the person claiming torque by itself is not important.
Fact us that torque is the only thing we can measure, so the only way to know the power curve is to measure the torque curve. So it is essential to proper engine tuning.
Originally Posted by KrisZ
If torque by itself is not important, then why is it that most engine designs seek to have the torque curve as flat as possible? Ideally you don't want it to be a curve at all, but rather a nice flat horizontal line.
Because a flat torque curve will result in a nice linearly increasing HP curve. Flat torque curves are achieved by making the engine volumetric efficiency (VE) as high and as constant as possible over the RPM range.
Yes, that's correct. I posed the question to the person claiming torque by itself is not important.
Fact us that torque is the only thing we can measure, so the only way to know the power curve is to measure the torque curve. So it is essential to proper engine tuning.
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