Horsepower and torque relationship

What's the difference between torque and horsepower? | HowStuffWorks

horsepower and torque relationship

I purchased a new car recently and in doing so became (for the first time) moderately curious about vehicle performance. I set about to see how. I had several requests to revisit this subject and explain the relationship between HP and torque across a broad range of frequencies. Mathematically, horsepower equals torque multiplied by rpm. exhaust cleanliness into the development equation and it's clear why engine.

James Watt came up with the concept of horsepower — which is a measure of, interestingly enough, power. Torque is nothing more than a measurement of twisting, or rotational, force. Hanging on the bottom of one end is a rope with a weight attached — a very heavy weight.

The Relationship Between Horsepower, Torque, and Acceleration | Daniel Miessler

Now imagine someone trying to, using their hands, twist the shaft so as to lift the weight. Think of them as essentially trying to act like a winch and reel it up. One unit for measurement of this is the foot-pound. The Common Mistake The mistake most people make when engaging in this debate is considering horsepower and torque independently. Almost everyone argues as if they are separate, unrelated values.

The fact of the matter is that horsepower is the product of torque and another value — RPMs divided by The Physics of Acceleration So now for the most important thing on the page. The formula for acceleration is seen below. 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.

horsepower and torque relationship

At 4, rpm, a lb-ft engine would already be making hp. 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.

What's the difference between torque and horsepower?

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. If the engine were to operate primarily under 5, rpm, says noted engine-builder David Reher, favoring a longer stroke helps get piston speed up.

That gives a better signal to the intake tract and makes the motor more responsive. The larger bore unshrouds the valves and depending on available cylinder head configurations, allows running bigger valves. With ultra-high-rpm over 8,normally aspirated racing engines, an extremely high-rpm power peak may slightly reduce the amount of peak torque compared to the same basic engine setup in street trim.

At the extremes, breathing restrictions due to reduced time to fill the cylinders and friction losses increase exponentially, leading to significant efficiency losses.

Anything you can do to reduce friction in a high-rpm engine is therefore extremely important. The short-stroke configuration in and of itself enhances engine durability by relieving cylinder wall thrust-loading, reducing piston speed, and reducing internal friction from what it otherwise would be with the long-stroke combo. Besides shortening the stroke, consider long rods, short pistons, low-friction rings, reduced bearing diameters, and positive crankcase evacuation.

The High-RPM Engine Horsepower is what gets you down the track quickly, and world-class professional race engines are built to achieve maximum horsepower.

horsepower and torque relationship

The extreme example are the tiny Formula I motors that make big power numbers but turn upward of 18, rpm to do it, and use seven-speed close-ratio gearboxes to stay within their narrow operating bands.

All that costs money…lots of money. And the inevitable result is that raising the torque peak to make more top-end horsepower means less torque down low. In this example, consider the shaft to be fixed to the wall. Let the arrow represent a lb. Because the shaft is fixed to the wall, the shaft does not turn, but there is a torque of pound-feet pounds times 1 foot applied to the shaft.

In the same way that one ton is a large amount of weight by definition, poundsone horsepower is a large amount of power. The definition of one horsepower is 33, foot-pounds per minute. Consider the following change to the handle-and-crank-arm sketch above.

The handle is still 12" from the center of the shaft, but now, instead of being fixed to the wall, the shaft now goes through the wall, supported by frictionless bearings, and is attached to a generator behind the wall. Suppose, as illustrated in Figure 2, that a constant force of lbs. In other words, the "arrow" rotates with the handle and remains in the same position relative to the crank and handle, as shown in the sequence below.

That is called a "tangential force". Figure 2 If that constant lb. The output shaft of the gearbox of the engine in Example 4 above turns at RPM. The point to be taken from those numbers is that a given amount of horsepower can be made from an infinite number of combinations of torque and RPM. Think of it another way: In fact, in cars of equal weight, the smaller engine will probably race BETTER because it's much lighter, therefore puts less weight on the front end.

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: Understanding the Relationship Between the Two, by EPI Inc.

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. 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?