my definition of torque:

Trying to take a pee in the morning with morning wood................

 

Torgue is simply the rotational force applied to an axis. If measured in pounds at a distance in feet from the axis (center of rotation), then it is expressed in foot pounds or pound feet. If measured in pounds and inches, then it is expressed as inch pounds (commonly used to compare cordless drills to each other). In the metric system it is measured in newtons (force) and meters (distance).

If you take a lug wrench with a 10 foot long handle for example, and apply 100 pounds of force to it exactly 1 foot from the lug center, you are generating 100 foot pounds of torque. If you apply 10 pounds of force 10 feet from the lug (i.e., at the end of the handle) you are also generating 100 foot pounds of torque. So you might say that it is easier to generate that 100 foot pounds of torque by applying 10 pounds to the end of a 10 foot lug wrench, rather than 100 pounds at 1 foot from the lug. Well, that's true, but to turn that lug one complete revolution, you will have to apply that 10 pounds of force through a distance of 62.83 feet, whereas with the 100 pounds at one foot you only have to apply the 100 pound force through a distance of 6.283 feet. If you can perform one rotation of the lug in the same amount of time for each case, you are generating the same amount of power.

One horsepower is the amount of power required to lift 550 pounds, 1 foot in one second or ((550 pounds x 1 foot)/second)). This was determined a long time ago as the amount of power the average horse could put out over a relatively long time. A human can put out one horse power for a few seconds, for example a weight lifter bench pressing 550 pounds one foot in one second would be one horsepower. If you lift 110 pounds 5 feet in one second you are also generating one horsepower. Since torque and horsepower are usually expressed as a function of revolutions per minute (RPM) not revolutions per second (RPS) it helps to think of one horsepower as the amount of power required to lift 33000 pounds, 1 foot in one minute, or 1 pound 33000 feet in one minute. This is just taking 550 x 60 seconds = 33000. Keep in mind that a circle with a radius of one foot has a circumference of 2 x PI or 6.2831853 feet. Also, 33000/6.2831853=5252. To determine the Horsepower, you need to know the torque (in foot pounds) at a given RPM using the equation HP = Torque x RPM/5252. To determine Torque, you need to know the Horsepower at a given RPM using the equation Torque = HP x 5252/RPM

So now think of the crankshaft of a V8 engine rated at 200 horsepower and 250 foot pounds of torque. The torque is the maximum twisting force that the V8 can generate (250 foot pounds) and this peak torque is only spec'd at a specific rpm. At all other rpms it is less. So lets say the 250 foot pounds of peak torque comes at 2500 RPM and that the 200 horsepower comes at 4500 RPM.

At 2500 RPM, 250 foot pounds is equivalent to lifting 250 pounds through a distance of 15707.963 feet in one minute (2500x 2 x PI, where PI =3.1415927). This is equivalent to lifting 1 pound a distance of 3926990.8 feet (250 x 15707.963). So dividing that by 33000 = 119 horsepower. A simpler way to do it is to first divide 33000 by 2xPI which equals 33000/6.2831853 = 5252. So then just take torque (in foot pounds) x rpm/5252, or 250 x 2500/5252=119 HP.

So if the V8 generates 200 HP at 4500 RPM, thats 200 x 5252/4500=233.4 foot pounds of torque.

So you can see that even though the V8 is generating less torque at 4500 RPM, it is generating 1.68 times as much horsepower as it does at 2500 RPM.

Another way to think of torque is the ability to create an increase in RPM. An engine with a large amount of torque at a low RPM but relatively low horsepower will have the ability to quickly increase that RPM, giving you that instant, neck snapping accelaration when you punch the throttle versus an engine with relatively low torque but high horsepower at high RPM, where when you punch the throttle the accelaration comes on in a more gradual but steady surge.

 

Well this is almost true, but one thing you have to include in this discussion is inertia. If the inertia of the engine and drivetrain is too high, your acceleration is low. A good example is a diesel engine. These engines crank out high torque at low rpm. And the throttle response is faster than a gas engine. However, one reason it cannot accelerate as fast because they typically have much higher inertia than the gas engines. Let me give you a starting equation:
Torque=Inertia*Acceleration
To state it another way, the acceleration is directly proportional to torque and inversely proportional to inertia.
BryceGTX