Horsepower vs Torque Explanation
Here is a great article that explains Horsepower vs Torque:
Horsepower vs. Torque at PRO Civic
Here are some exerts from the article:
Originally Posted by www.procivic.com
Deriving the Relationship
To be clear, torque is a force that causes something to rotate. That something is usually circular, but it doesn't have to be. The distance part of torque is also called a lever-arm (or moment arm). The lever-arm acts to multiply the force being exerted. Think of opening a door, if you try pushing near the hinge, it takes a lot more force than pushing form near the handle. The distance from where you push to the hinge is the length of the lever-arm. Again, don't confuse torque with work. Think of torque as an instantaneous push on the door, where as work would be pushing the door over a distance.
Horsepower is how quickly you can apply torque over a given distance. Watt's definition says that 1 hp = 550 ft-lb/s. Now, how do we convert horsepower into something that relates to torque and engine rpm? Well, keep in mind that horsepower is force times distance divided by time, and our distance is going to be in a circle (i.e. in revolutions)....
While talking to BenFenner he mentioned this example
Originally Posted by BenFenner
BenFenner: ...Torque can be though of as a puff of air pushing on the back of the car. Power is how many puffs of air you get per second...
....
BenFenner: Torque is the strength of the single puff of air.
BenFenner: Power is how many you get per second.
BenFenner: So having 1,000 ft lbs of torque from an electric engine at 0 rpm is like having a huge puff of air zero times a second. =/
Originally Posted by www.procivic.com
horsepower = torque * rpm / 5252
Now you know exactly how horsepower and torque are related. There are no exceptions to this rule; they will always be related by this formula. In fact, it might be better to see them as just flip sides of the same coin. One result of this formula is that below 5252 rpm, torque will always be more than horsepower, at 5252 rpm they will be equal, and above 5252 rpm torque will be less. Note that a dyno never measures horsepower; it can only measure torque and then use the above formula to get horsepower.
Originally Posted by www.procivic.com
Acceleration
So we now know that horsepower and torque are basically two different views of the same thing - change one and the other most also change. What we are really interested in is how they work together to affect a car's overall acceleration. Using Newton's Second Law, we know that F = ma.
....
So, our acceleration at any given moment is only dependent on the torque at the wheels (again, assuming that traction is not broken). That means the acceleration of the car is constantly changing to match the torque curve, and the car accelerates hardest at the torque peak. The name of the game is to keep your car producing as much torque as possible, for the longest amount of time possible. That will give you the best acceleration and fastest quarter mile times.
Now to stray away a little, this is why we dyno in 1:1 gears (Meaning the transmission is not multiplying torque). As mentioned earlier a dyno doesn't measure Horsepower, it measures torque then converts it into a Horsepower number. If you were to dyno in a non 1:1 gear, aka lower gear, then torque numbers would be higher, thus a dyno would see higher HP numbers, when in reality your HP would still be the same.
Originally Posted by www.procivic.com
The Transmission Effect
Now comes the tricky part: the transmission. The fact that our engines cannot rev indefinitely means we must have transmissions to allow our wheels to keep spinning faster while keeping the revs under redline. A transmission essentially makes engine torque meaningless because it can multiple your flywheel torque to any amount it pleases, and is only limited by physical gear size. This is because gears can be arranged to increase or decrease their lever-arms and thus change the final torque output.
However, don't go out and buy yourself a giant gear set just yet: transmissions cannot amplify horsepower. This would violate the law of conservation of energy and change the world as we know it. Instead, as we increase the torque output for a certain gear, we decrease the maximum speed that we can have in that gear. Would you want your Honda Civic to have 400 lb-ft of torque in 1st gear but only be able to go 8 mph in that gear? Probably not. The opposite is also true; as you decrease the torque output of a certain gear, you increase maximum speed, assuming you can reach it. That is the main reason why you accelerate slower in higher gears.
Originally Posted by www.procivic.com
The Verdict
So what advantage does a higher horsepower engine have compared to a lower one, assuming they both have similar torque curves? In short, the higher horsepower one will perform much better. The car with the high-reving, high-horsepower engine can run a more aggressive set of gears while still being able to spend the same amount of time in each gear as the slower car. This will give it better overall acceleration because of increased torque to the wheels. If both cars run the same gears, then the high-power one will be able to spend a shorter time in each gear, giving it better overall acceleration. Either way, it is an advantage. If you take away anything from this article, let it be that gearing is extremely important in determining a car's overall performance.
Taking advantage of horsepower, don't cut yourself short by shifting at peak torque. Even shifting at peak Horsepower might not be a good idea. Check your car's dynograph, if your power is not falling off majorly after peak Horsepower, take the car to redline!
Originally Posted by www.procivic.com
As far as shifting goes, always shift to maximize transmission output torque. It turns out this is exactly the same as saying shift to maximize engine power. Never shift at torque peak, even if your best friend tells you he swears it's faster that way. You will lose the overall higher torque of the current gear and it will also put you in a worse spot in the next gear. Most cars (Honda Civics included) will obtain their best quarter mile times by shifting at redline, but it is not true for every car. For some cars, it is necessary to look at a dyno graph to really see where the best point is.
While this is true, keep in mind this applies mostly for racing. If you daily drive or tow, having more torque helps tremendously because it's low end horsepower!
Originally Posted by www.procivic.com
And that's it. Now if someone claims your Honda Civic can't go fast because it doesn't have enough torque, you can prove them wrong!
Horsepower vs. Torque at PRO Civic
Here are some exerts from the article:
Originally Posted by www.procivic.comDeriving the Relationship
To be clear, torque is a force that causes something to rotate. That something is usually circular, but it doesn't have to be. The distance part of torque is also called a lever-arm (or moment arm). The lever-arm acts to multiply the force being exerted. Think of opening a door, if you try pushing near the hinge, it takes a lot more force than pushing form near the handle. The distance from where you push to the hinge is the length of the lever-arm. Again, don't confuse torque with work. Think of torque as an instantaneous push on the door, where as work would be pushing the door over a distance.
Horsepower is how quickly you can apply torque over a given distance. Watt's definition says that 1 hp = 550 ft-lb/s. Now, how do we convert horsepower into something that relates to torque and engine rpm? Well, keep in mind that horsepower is force times distance divided by time, and our distance is going to be in a circle (i.e. in revolutions)....
While talking to BenFenner he mentioned this example
Originally Posted by BenFennerBenFenner: ...Torque can be though of as a puff of air pushing on the back of the car. Power is how many puffs of air you get per second...
....
BenFenner: Torque is the strength of the single puff of air.
BenFenner: Power is how many you get per second.
BenFenner: So having 1,000 ft lbs of torque from an electric engine at 0 rpm is like having a huge puff of air zero times a second. =/
Originally Posted by www.procivic.comhorsepower = torque * rpm / 5252
Now you know exactly how horsepower and torque are related. There are no exceptions to this rule; they will always be related by this formula. In fact, it might be better to see them as just flip sides of the same coin. One result of this formula is that below 5252 rpm, torque will always be more than horsepower, at 5252 rpm they will be equal, and above 5252 rpm torque will be less. Note that a dyno never measures horsepower; it can only measure torque and then use the above formula to get horsepower.
Originally Posted by www.procivic.comAcceleration
So we now know that horsepower and torque are basically two different views of the same thing - change one and the other most also change. What we are really interested in is how they work together to affect a car's overall acceleration. Using Newton's Second Law, we know that F = ma.
....
So, our acceleration at any given moment is only dependent on the torque at the wheels (again, assuming that traction is not broken). That means the acceleration of the car is constantly changing to match the torque curve, and the car accelerates hardest at the torque peak. The name of the game is to keep your car producing as much torque as possible, for the longest amount of time possible. That will give you the best acceleration and fastest quarter mile times.
Now to stray away a little, this is why we dyno in 1:1 gears (Meaning the transmission is not multiplying torque). As mentioned earlier a dyno doesn't measure Horsepower, it measures torque then converts it into a Horsepower number. If you were to dyno in a non 1:1 gear, aka lower gear, then torque numbers would be higher, thus a dyno would see higher HP numbers, when in reality your HP would still be the same.
Originally Posted by www.procivic.comThe Transmission Effect
Now comes the tricky part: the transmission. The fact that our engines cannot rev indefinitely means we must have transmissions to allow our wheels to keep spinning faster while keeping the revs under redline. A transmission essentially makes engine torque meaningless because it can multiple your flywheel torque to any amount it pleases, and is only limited by physical gear size. This is because gears can be arranged to increase or decrease their lever-arms and thus change the final torque output.
However, don't go out and buy yourself a giant gear set just yet: transmissions cannot amplify horsepower. This would violate the law of conservation of energy and change the world as we know it. Instead, as we increase the torque output for a certain gear, we decrease the maximum speed that we can have in that gear. Would you want your Honda Civic to have 400 lb-ft of torque in 1st gear but only be able to go 8 mph in that gear? Probably not. The opposite is also true; as you decrease the torque output of a certain gear, you increase maximum speed, assuming you can reach it. That is the main reason why you accelerate slower in higher gears.
Originally Posted by www.procivic.comThe Verdict
So what advantage does a higher horsepower engine have compared to a lower one, assuming they both have similar torque curves? In short, the higher horsepower one will perform much better. The car with the high-reving, high-horsepower engine can run a more aggressive set of gears while still being able to spend the same amount of time in each gear as the slower car. This will give it better overall acceleration because of increased torque to the wheels. If both cars run the same gears, then the high-power one will be able to spend a shorter time in each gear, giving it better overall acceleration. Either way, it is an advantage. If you take away anything from this article, let it be that gearing is extremely important in determining a car's overall performance.
Taking advantage of horsepower, don't cut yourself short by shifting at peak torque. Even shifting at peak Horsepower might not be a good idea. Check your car's dynograph, if your power is not falling off majorly after peak Horsepower, take the car to redline!
Originally Posted by www.procivic.comAs far as shifting goes, always shift to maximize transmission output torque. It turns out this is exactly the same as saying shift to maximize engine power. Never shift at torque peak, even if your best friend tells you he swears it's faster that way. You will lose the overall higher torque of the current gear and it will also put you in a worse spot in the next gear. Most cars (Honda Civics included) will obtain their best quarter mile times by shifting at redline, but it is not true for every car. For some cars, it is necessary to look at a dyno graph to really see where the best point is.
While this is true, keep in mind this applies mostly for racing. If you daily drive or tow, having more torque helps tremendously because it's low end horsepower!
Originally Posted by www.procivic.comAnd that's it. Now if someone claims your Honda Civic can't go fast because it doesn't have enough torque, you can prove them wrong!
Last edited by Vadim
on 2011-11-15
at 19-37-01.
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