Power and torque relationship

Power, Torque and Speed Relation

power and torque relationship

This means that torque that is causing the angular speed to increase is doing work and the generated power may be calculated as: Mathematically, the equation. The following calculations show the relationship between power, torque and rotational speed as the rotational motion passes through the gearbox, with power in. Most commercials you see for big trucks advertise the impressive amount of horsepower and torque the engine provides. It seems, as usual, the bigger the.

For example, if you use a hoist to lift a pound engine 6 feet in the air, the work done would be 6 feet x pounds or 3, foot-pounds ft-lb.

Engine Power Delivery – What is Torque Vs. Horsepower

But engines as well as nuts and bolts when they are tightened or loosened rotate around an axis. What is engine torque? The expression of this rotational or twisting force around an axis is called torque, which is measured in units of force times distance from the axis of rotation.

If you have a 1-foot-long wrench and you exert a force of 10 pounds on the end of it then you apply a torque of 10 pound-feet 10 lb-ft. If the wrench were 2 feet long, the same force would apply a torque of 20 lb-ft.

To avoid confusion in the U. Just recall your geometry: With a 1-foot lever: The more power that is generated, the more work is done in a given time-period. Suppose it takes a constant lb-ft of torque to spin a nut onto a bolt one complete revolution. Your girlfriend takes 10 seconds to do this. You, being a real stud pun intendedtake only 5 seconds to perform the same task.

You would be twice as powerful, because you performed the same work in half the time. Here, D is the distance in feet the weight is to be moved; F, the force in pounds required to move the weight; and t, the time in minutes required to move the weight F through distance D. The result is the classic equation with which we are all familiar. Suppose an engine makes lb-ft at 3, rpm. The equation tells us that at 3, rpm it would produce hp.

power and torque relationship

But if the engine made lb-ft at 6, rpm, it would produce hp. It is simply unrealistic to expect a normally aspirated engine to produce both big torque and big power numbers under 6, rpm-unless the engine is really huge. For example, I was contacted by a reader who wanted to build a big-block Chevy not exactly a small-fry!

What is Torque vs. Horsepower - Engine Power Delivery Explained - Hot Rod - Hot Rod Network

In round numbers, that means the torque peak usually occurs 1, rpm below the horsepower peak-so for power to peak at 5, rpm, the torque peak would be no higher than 4, rpm. At 4, rpm, a lb-ft engine would already be making hp.

power and torque relationship

Theoretically, this combo would be on the way to making hp. Actual dyno tests show that a mechanical roller cam 0. This car is competitive with the high-compression, high-rpm and ci engines in his class, but it lasts longer and requires less maintenance.

The big inches just mean you make more torque earlier, which means big horsepower sooner. In other words, the most effective way to raise torque output is to increase engine size.

AND, in reality, the car with the lighter 2-liter engine will likely weigh less than the big V8-powered car, so will be a better race car for several reasons.

power and torque relationship

Measuring Power A dynamometer determines the POWER an engine produces by applying a load to the engine output shaft by means of a water brake, a generator, an eddy-current absorber, or any other controllable device capable of absorbing power. Then it applies various factors air temperature, barometric pressure, relative humidity in order to correct the observed power to the value it would have been if it had been measured at standard atmospheric conditions, called corrected power.

What's the difference between torque and horsepower?

Power to Drive a Pump In the course of working with lots of different engine projects, we often hear the suggestion that engine power can be increased by the use of a "better" oil pump. Implicit in that suggestion is the belief that a "better" oil pump has higher pumping efficiency, and can, therefore, deliver the required flow at the required pressure while consuming less power from the crankshaft to do so.

While that is technically true, the magnitude of the improvement number is surprisingly small. How much power does it take to drive a pump delivering a known flow at a known pressure? We have already shown that power is work per unit time, and we will stick with good old American units for the time being foot-pounds per minute and inch-pounds per minute.

power and torque relationship

Since flow is more freqently given in gallons per minute, and since it is well known that there are cubic inches in a gallon, then: Since, as explained above, 1 HP is 33, foot-pounds of work per minute, multiplying that number by 12 produces the number of inch-pounds of work per minute in one HPDividingby gives the units-conversion factor of Therefore, the simple equation is: When the equation is modified to include pump efficiency, it becomes: So suppose your all-aluminum V8 engine requires 10 GPM at 50 psi.

The oil pump will have been sized to maintain some preferred level of oil pressure at idle when the engine and oil are hot, so the pump will have far more capacity than is required to maintain the 10 GPM at 50 psi at operating speed. That's what the "relief" valve does: It is actually pumping roughly 50 GPM 10 of which goes through the engine, and the remaining 40 goes through the relief valve at 50 psi. The power to drive that pressure pump stage is: That pump at the same flow and pressure will consume: General Observations In order to design an engine for a particular application, it is helpful to plot out the optimal power curve for that specific application, then from that design information, determine the torque curve which is required to produce the desired power curve.

By evaluating the torque requirements against realistic BMEP values you can determine the reasonableness of the target power curve. Typically, the torque peak will occur at a substantially lower RPM than the power peak. For a race engine, it is often beneficial within the boundary conditions of the application to operate the engine well beyond the power peak, in order to produce the maximum average power within a required RPM band.

However, for an engine which operates in a relatively narrow RPM band, such as an aircraft engine, it is generally a requirement that the engine produce maximum power at the maximum RPM. That requires the torque peak to be fairly close to the maximum RPM. For an aircraft engine, you typically design the torque curve to peak at the normal cruise setting and stay flat up to maximum RPM.

That positioning of the torque curve would allow the engine to produce significantly more power if it could operate at a higher RPM, but the goal is to optimize the performance within the operating range.

An example of that concept is shown Figure 3 below. The three dashed lines represent three different torque curves, each having exactly the same shape and torque values, but with the peak torque values located at different RPM values.

The solid lines show the power produced by the torque curves of the same color. Again, moving the same torque curve to the right another RPM blue, lb-ft torque peak at RPM causes the power to peak at about HP at RPM Using the black curves as an example, note that the engine produces HP at both and RPM, which means the engine can do the same amount of work per unit time power at as it can at The RPM band within which the engine produces its peak torque is limited.

You can tailor an engine to have a high peak torque with a very narrow band, or a lower peak torque value over a wider band.