# Horsepower and rpm relationship

### Relation between torque and rpm | Physics Forums

The following calculations show the relationship between power, torque and velocity in radians/sec, T is torque in N.m, and n is rotational speed in rpm. Power-Torque. Torque (changethru.info) = 63, x Power (HP) / Speed (RPM). Power (HP) = Torque (changethru.info) x Speed (RPM) / 63, Torque (N.m) = x Power (kW). Not really any direct correlation - you cannot take RPM (revs er minute), multiply or divide by something to get HP (horsepower) - however as a GENERAL rule.

The red line has a torque peak at about It will feel sluggish from a stop and seem to wake up as the rpms increased. From tothe red engine will out-accelerate the solid engine by a significant margin. This is roughly what we would expect from a smaller engine and forced injection would only increase this late-rpm peak.

## - Power and Torque -

The question for the customer is: The early torque peak of the solid line is fun from a standing start but you will need to shift early trading mechanical advantage to get back to the torque peak. Hopefully, you have enough gears to get you to top speed. This profile is often preferred in a street car. The later peaks of the dotted line is sluggish from a standing start but becomes progressively more exciting as revs increase.

But remember, the transmission ultimately gives the force to the wheels, not the engine. The torque at the wheels is the torque at the engine combined with the torque magnification given by the transmission through gearing.

And RPMs are what allow us to use gearing effectively, which gives us more torque at the wheels. Notes For any comments, corrections, flames, or other types of input, feel free to contact me.

Gearing is extremely important because it controls RPMs and therefore horsepower. Gears magnify torque — hence the acceleration available in first gear. Low torque, high horsepower. Another excellent explanation of the topics at allpar.

But it runs out quickly. Racecars have high horsepower due to high RPMs, not due to high torque see gearing. At RPMs the horsepower and torque will be exactly the same.

### How to Calculate Horsepower & RPM | Sciencing

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.

जानिए Torque / bHP / RPM के बारे मे -

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. Those characteristics are usually dictated by the parameters of the application for which the engine is intended. An example of that is shown in Figure 4 below.

It is the same as the graph in Figure 3 aboveEXCEPT, the blue torque curve has been altered as shown by the green line so that it doesn't drop off as quickly.

Note how that causes the green power line to increase well beyond the torque peak. Alterations intended to broaden the torque peak will inevitable reduce the peak torque value, but the desirability of a given change is determined by the application. Figure 4 Derivation of the Power Equation for anyone interested This part might not be of interest to most readers, but several people have asked: First, determine the distance it moves in one revolution: Now we know how far the crank moves in one revolution.