Torque and Horsepower?

Question

Can someone please tell me in detail what is torque and what is horsepower? Also how can an engine produce more torque in the pistons at a lower rpm than high rpm? How is torque tested? How is horsepower the most at 7,000 rpm rather than maximum? Wouldn't the engine be able to handle more at a higher rpm? Basically i jus want a detailed explanation of torque and horsepower and how then engine produces more torque at lower rpm and higher horsepower not at the redline?

Answer 1

Measures of engine performance such as torque and horsepower are relatively simple, yet are often badly misunderstood by the public. Some of this misunderstanding is due to automobile advertising, some to people having just enough knowledge to be dangerous, and some to the continuing death-spiral of science education in America. I'll begin by explaining power vs. horsepower, then torque and how it is related to power. Finally I'll give examples of why knowing something about these concepts is important when comparing automobile engines.

First, let’s note that horsepower is a unit of measurement for power, in the scientific sense of the term, just as the foot is a unit of measurement for length. Horsepower measures the same thing that the watt does--the power that a device can create or consume. Just as the wattage of a light bulb tells you how much power it will use, the horsepower specification for an engine tells you how much power the engine can produce.

Power is measured in many other units besides horsepower, depending on location and application. Watts (W) and kilowatts (kW) are in common use worldwide. Less common measures include British thermal units per hour (Btu/hr) and foot-pound force per minute (ft-lbf/min). Since any or all of these could be valid performance measures, technically it's more correct to talk about an engine's power than its horsepower. However, in practice most people in the United States use the two words synonymously.

Standard mechanical horsepower is defined as about 33,000 ft-lbf/min, or 745.7 watts. However, there are many different official and unofficial definitions of horsepower. Some of these definitions refer to different ways of measuring power for a specific application. For example:

* “Brake horsepower” generally means that the power was measured on a type of dynamometer called a “prony brake" (sometimes incorrectly called a “pony brake”--prony refers to the inventor, Gaspard de Prony)
* “Drawbar horsepower,” used in railroad applications
* “Air horsepower,” used in fan calculations.

Some types of horsepower define power at different magnitudes. Listing them in terms of relationship to the standard horsepower, we see:
Definition Watts ft-lbf/min
Horsepower (also called “standard” or “mechanical”) 745.7 33,000
Boiler horsepower 9,809.5 434,107
Electric horsepower 746 33,013.3
Metric horsepower 735.499 32,548.6
Water horsepower 746.043 33,015.2

How did we end up with the “horse” in horsepower? The term was coined by James Watt (1736-1819), the British inventor best known for his improved steam engines, who used the term to relate steam engine performance to that of horses. At the time horses were the primary energy source for applications ranging from pumping water from mines and turning grinding mill wheels to pulling carts and loads. Although sources differ on exactly how Watt arrived at the number, it’s generally thought that in 1782, he noted how quickly a brewery horse could turn a mill wheel of a certain radius, estimated the amount of force the horse needed to exert to turn the wheel, did the math, and came up with a value of 32,400 ft-lbf/min, later rounded to 33,000 ft-lbf/min. Comparing the power output of a steam engine to an equivalent number of horses was an easy way for prospective engine purchasers to compare power ratings, so the term stuck.

What type of horse was a brewery horse? In England at the time a work horse most likely would have been one of the three British "heavy breeds" – the Suffolk punch, the shire horse, and the Clydesdale. The Clydesdale is said to have originated in the latter 1700s, perhaps too late to be a common work horse at the time Watt was doing his horsepower calculations. So it seems likely the horse in question was either a Suffolk punch or a shire horse.

Now let’s talk torque. Torque is turning force, which for automotive applications is most often measured in either foot-pounds (ft-lbf) or Newton-meters (N-m). Sometimes these are written as lbf-ft or m-N, a convention some use to differentiate torque from work, since they involve the same units . . . but I digress.

Here's a simple way to visualize torque: Imagine holding a 1-pound weight straight out, with your arm parallel to the ground. My arm measures about two feet from shoulder to wrist. If I hold a 1-pound weight straight out, the torque my shoulder experiences is roughly 2 foot-pounds (2 feet times 1 pound). If I were to hold a 10 pound weight in my hand, then the torque on my shoulder would be roughly 20 foot-pounds (2 feet times 10 pounds).

Now think of this turning force applied to a wheel, such as if a lever was attached to the center of an automobile wheel. The more force you apply on that lever, the more torque you apply to the wheel, the more readily the wheel turns, and the faster the car starts moving. See where I’m going with this? Torque is a measure of the ability of an engine to do work. It's a component of, but not the same as, the (horse) power of the engine, which is the rate at which work can be done. In an automotive engine, power and torque are related by a simple equation that considers torque, engine speed (in revolutions per minute), and a conversion factor:

In this equation, torque is expressed in terms of ft-lbf, the engine speed is given in revolutions per minute, and 5252 is a conversion constant. An engine's horsepower, then, isn't constant, but rather varies with its speed. The numbers you see quoted in brochures and so on indicate peak horsepower. Such figures can be misleading, as we shall now see.

Let’s say we're trying to decide between Engine A and Engine B for a high-performance car. Here's a chart showing the peak power and torque for each engine:

Power, hp Torque, ft-lbf
Engine A

224


300
Engine B

247


210


At first glance, Engine B looks like the better choice – it has 23 more peak horsepower! However, a graph of the power curves of these two engines, showing their power as a function of engine speed. Although Engine B has more peak horsepower, Engine A has more power at speeds up to 5500 rpm. What's more, it has significantly more power in the 1500-4000 rpm range (highlighted area), the range of engine speeds in which you'd typically operate a car.

Now let's talk about the torque curves of the two engines:

Engine A puts out much greater torque, especially over the typical engine speed range, indicating that under normal conditions Engine A will give you much more “oomph” than Engine B. Peak numbers are nice to brag about but often don't mean much, since few people operate their engines at peak conditions (which would generally be full throttle) in a typical day.

I'm oversimplifying things with this example, as many other factors come into play when selecting an engine, such as fuel efficiency, emissions, weight, cost, etc. Depending on circumstances, a performance enthusiast or racer might opt for Engine B, especially if she can mate it with transmission gearing that will take advantage of the power available at high engine speeds. But how many of us are shopping for that kind of performance when we head down to the dealership for the ritual shakedown known as buying a new car?

Answer 2

Torque by definition is the ability to twist or turn,so torque is a car/truck is what gets the vehicle moving, Horsepower is a rating the measures the engines overall power 1 HP means the engine can more 33 thousand pounds 1 foot in 1 minute. The answer to the redline and torque curve questions is simple. A motor with low rpm torque is a work vehicle(diesel,big block v-8's mainly) High rpm HP usually a 4 cylinder car. The reasons why the engines make power at these specific rpms' is a list a mile long, they have to do with (compression, cam shaft measurments,piston design,ignition timing and spark strength..there are TONS of reasons) All cars are built with a specific purpose in mind and the motors chosen for the aplication are with good reason. If you question why become an engineer and change everything lol

Answer 3

Not quite. Horsepower is the potential ability to do work and how much. Torque is the twisting force applied in the case of a car to the wheels. Loads of horsepower without torque = no movement at all. Torque can be multiplied by the gearing and is in all automotive applications. generally the best performance in a car or on a bike is when the gearbox is used to keep the engine spinning between the lower highest torque rev speed and the higher best power rev speed. There is no magic formula but it is fair to say that with a reasonable amount of torque available them power output will determine top speed if all other things are equal. In vehicles the rolling resistance, mass and drag are what the power has to overcome with the result that a high torque 600 bhp volvo lorry is a lot slower than a 50 bhp motorcycle. As you can see because of this there is no direct correlation between power torque and speed.

Answer 4

Torque is a twisting force. Torque is measured in lb-ft.

Horsepower is = torque x rpm '/. 5252
or 33,000 ft-lb or work per min
One HP = 746 Watts
Engine HP rises as the RPM goes up, but only until the inertia of the fuel air mix cannot be drawn into the combustion chamber because of valve timing. HP drops off when the engine breathing is too poor to draw in more fuel air mix.
Max. Torque usually occurs at a lower engine RPM because
the fuel air mix can create a better charge for ignition and cylinder pressure rise, (combustion) with which to push the piston downwards during the power stroke.

Answer 5

Torque is part of the basic specification of an engine: the power output of an engine is expressed as its torque multiplied by its rotational speed. Internal-combustion engines produce useful torque only over a limited range of rotational speeds (typically from around 1,000–6,000 rpm for a small car). The varying torque output over that range can be measured with a dynamometer, and shown as a torque curve. The peak of that torque curve usually occurs somewhat below the overall power peak. The torque peak cannot, by definition, appear at higher rpm than the power peak.

Understanding the relationship between torque, power and engine speed is vital in automotive engineering, concerned as it is with transmitting power from the engine through the drive train to the wheels. Typically power is a function of torque and engine speed. The gearing of the drive train must be chosen appropriately to make the most of the motor's torque characteristics


http://en.wikipedia.org/wiki/Torque
This explains it pretty good. Click the shortcut.