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Horsepower

What is Horsepower?
A typical car in America has something around a 120-horsepower engine. A big SUV might have a 200-horsepower engine, and a tiny car might have only 70 horsepower. A moped, on the other hand has only a 1- or 2- horsepower engine, and it gets great gas mileage -- 70 or 80 miles per gallon. So why not put a little engine in a car to give its mileage a boost?

2013 Chevrolet Caprice Specifications

Horsepower:301hp @ 6,700RPM
Fuel tank capacity:19.0gal.
Torque:265 lb.-ft. @ 4,800RPM

How to Increase a Car Engine's Horsepower

A car engine's horsepower is its raw strength, its ability to move the vehicle quickly, accelerate past trouble and haul increasingly large loads. Though stock engines from the dealer often provide plenty of horsepower to move the vehicle in question, you can increase the horsepower your engine generates by employing a few basic modification strategies.

Instructions

1 Increase the size of your car's air filter or reduce the size of its intake piping. This allows air to enter the engine more freely, which lets the pistons work more efficiently and increases the engine's horsepower.

2 Replace your intake manifold with one made of smoother material, or simply polish it to buff out any imperfections. That will lower the air's resistance as it moves into the engine's pistons and increase its effective horsepower.

3 Add a high-performance exhaust system to your car. The engine's exhaust must exit as freely as possible, or else it causes the car to lose horsepower. The inclusion of a header, a free-flowing muffler or a larger tail pipe--all components of a high-performance exhaust system--will reduce the air resistance out of your engine and help exhaust to escape.

4 Install an intercooler. Cool air contracts, which means you can fit more of it into the engine's cylinder than hot air. The more air you fit in the engine, the more horsepower when the cylinder fires. An intercooler is the most effective way to achieve this, though some high-performance cars already have them installed.

5 Add a turbo charger to the car engine. Turbo chargers compress the air entering the engine, which adds more oxygen to the combustion process and will increase the power under the hood.

6 Switch the engine's head with one that has multiple intake values and exhaust valves. Most standard engines only have one of each. With multiple valves, the engine's airflow will increase and the horsepower will improve.

7 Exchange the ROM chip in the engine control unit of the car. However, this technique is only applicable to late-model cars, and it isn't always guaranteed to increase the horsepower. Check the chip carefully before you purchase it and get an independent opinion on its quality, if possible.

8 Decrease the weight of the car. The lighter the vehicle, the faster it moves and the more effective its existing horsepower. You can do this by replacing individual elements with lighter materials or simply by unloading some of the detritus you may be carrying around in the back seat or the trunk.

How do you define horsepower?

Horsepower (HP) is a measure of how much power is being produced from a motor. 1 HP is equal to 550 foot-pounds per second or 746 Watts. An actual horse puts out about 15 HP at max speed and about 1 HP for sustained activity. All though a car's weight and torque play a huge roll in its speed, horsepower ultimately determines the power. (the power that a device can create or consume.)

What's the difference between horsepower and torque?

The power an engine produces is called horsepower. In mathematical terms, one horsepower is the power needed to move 550 pounds one foot in one second, or the power needed to move 33,000 pounds one foot in one minute. Power, in physics, is defined simply as the rate of doing work.

Engine horsepower is measured using a dynamometer. The dynamometer places a load on the engine and measures the twisting force the engine crankshaft places against the load. The load is usually a brake preventing the wheels from spinning.

What the dynamometer is really doing, however, is measuring the torque output of the engine. In a vehicle, torque is measured at various engine speeds, or revolutions per minute (RPM). These two numbers are fed into a formula -- torque times RPM divided by 5,252 -- to arrive at horsepower. The Society of Automotive Engineers has two standards for determining horsepower: net and gross. Gross horsepower removes most loads from the engine, including emission controls, before testing. Net horsepower is what's found by testing the same kind of stock vehicle you'd find at the showroom, and that's the measurement now used in advertising and manufacturer literature.

Horsepower is determined from torque because torque is easier to measure. Torque is defined specifically as a rotating force that may or may not result in motion. It's measured as the amount of force multiplied by the length of the lever through which it acts. For example, if you use a one-foot-long wrench to apply 10 pounds of force to a bolt head, you're generating 10-pound-feet of torque.

Torque, as mentioned above, can be generated without moving an object. However, when it does move an object, it then becomes "work," and this is what most people think of when they think of torque (usually in terms of towing). The more torque produced by an engine, the more work potential it has.

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).

Mechanical horsepower hp(I)

Metric horsepower
hp(M) - also PS, ''cv, hk, pk, ks or ch

Electrical horsepower hp(E)

Boiler horsepower hp(S)

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

Hydraulic horsepower

In certain situations it is necessary to distinguish between the various definitions of horsepower and thus a suffix is added: hp(I) for mechanical (or imperial) horsepower, hp(M) for metric horsepower, hp(S) for boiler (or steam) horsepower and hp(E) for electrical horsepower.

One mechanical horsepower also equals 745.699 watts or .746 kW (kilowatts) of electrical horsepower.

Hydraulic horsepower is equivalent to mechanical horsepower. Convert Thrust to Horsepower

Is it possible to covert between pounds of thrust and horsepower for an airplane engine? How is it done?

One of the most frequent questions we receive concerns the difference between thrust and horsepower and how to convert between the two. The problem is that these quantities are not directly related, so it is not simple to convert one to the other. The dictionary defines thrust as a force or pressure exerted on an object, and it is typically measured in units of pounds (lb) or newtons (N). Power, however, is a measurement of work, which is defined as the amount of motion a force creates when it is exerted on a body over a certain amount of time. Power is typically measured in units of horsepower (hp) or kilowatts (kW). The most common equation used to relate these quantities is as follows.
where
P = power
F = force
d = distance
t = time

To understand what these definitions mean, let's consider a simple example. Say you had to move a heavy desk 10 ft (3 m) from one side of the room to another. You push on the desk with a force of 90 lb (400 N), but the desk doesn't budge. In this case, a force has been applied, but since the desk remains in the same place, you didn't perform any work. Now you ask a friend to help you, and he pushes on the desk with the same force as you. Your combined force of 180 lb (800 N) allows you to move the desk to its new location in half a minute (30 seconds).vv Based on the above equation, the power you and your friend generated to perform that work was 60 foot-pounds per second or 80 newton-meters per second. In the Metric system, the unit of a watt (W) is defined as a newton-meter per second, so the power it took to move the desk is 80 W or 0.08 kW. The English system equivalent of a watt is horsepower, and 1 hp is defined as being equal to 550 ft-lb/s. In other words, our 60 ft-lb/s is equivalent to 0.11 hp. In this case and this case only, we can say that a force of 180 lb converts to 0.11 hp. As we have seen, however, that conversion depends on the variables distance and time. If you and your friend used the same force to move the desk the same distance but it took only 15 seconds, the power would double to 0.22 hp (0.16 kW).

We can also think of this equation in two slightly different ways. Some readers may recognize that the force multiplied by distance represents another quantity called torque (T), so we can say power is equivalent to the torque a system generates over time.

Others may recognize the term distance over time as the definition of velocity (v), so we can also say that power is equivalent to the force it takes to move an object at a constant speed.

It is these two forms of the power equation that are most applicable to aviation. For example, one of the common types of question we receive asks how to convert the pounds of thrust generated by the jet engine(s) on a particular plane into horsepower. The first factor we must consider is that the thrust figures provided for most planes are in "static" units. Consider for a moment the Boeing 747-200 with its Pratt & Whitney JT9D turbofans. These four engines generate a total static force rating of 219,000 lb (973 kN). However, this force is measured by placing the engine on a device called a test stand.

A simple propulsion test stand is conceptually no different than standing on a bathroom scale and measuring how much you weigh, or how much force you exert standing on the surface of the Earth. The stand is fixed to the ground and an engine is strapped onto it. When turned on, the engine pushes against a scale (or load cell) that measures how much force the engine produces. Since the engine doesn't actually move but is rigidly held in place, we say that the force measured by the stand is in static pounds, or newtons, of force.

How much power does the 747's Pratt & Whitney engine produce? As we discussed earlier, a static engine does no work no matter how much thrust it produces because it results in no motion. We must instead focus our attention on a plane that is in motion. For example, our 747 typically cruises around 600 mph (970 km/h). However, we are faced with a new problem because the plane does not necessarily need every bit of its static thrust to fly at that speed. In fact, static thrust is really an ideal maximum amount of thrust that an engine can produce in a test environment. As discussed in a previous question about thrust ratings, any jet engine will produce less thrust in actual use than the static value.

Furthermore, aircraft are equipped with throttles that allow a pilot to adjust the amount of thrust an engine produces. A good example is the SR-71 Blackbird equipped with Pratt & Whitney J58 turboramjets that produced a combined static thrust of 65,000 lb (289 kN). Even though the Blackbird could reach speeds in excess of Mach 3, however, it actually needed very little of this thrust in cruise flight. Most of the thrust was required to accelerate through the speed of sound, but once at Mach 3, the SR-71 engines were throttled back to only 30% or so.

The conclusion of this explanation is that in order to determine the power a jet creates in flight, we need to know the exact amount of thrust necessary to fly at a particular speed. We typically know the static thrust rating of an engine or the airspeed of a plane during flight, but the problem is that we usually don't know the amount of thrust that corresponds to a particular speed at a specific point in time. It is because of this disconnect that it is so difficult to calculate the power generated by the engines on a particular plane.

Luckily, we do have access to data from a NASA report that does provide all the data we need to illustrate a sample case. The data is provided for a Boeing 747-200 cruising at Mach 0.9 at 40,000 ft (12,190 m). In this example, the aircraft's engines produce 55,145 lb (245,295 N) of thrust, only a quarter of its rated static thrust, to cruise at a velocity of 871 ft/s (265 m/s). Using the equations provided above, we calculate the power generated by the 747 to be 87,325 hp (65,100 kW).

The NASA data also includes a few other planes, so let's compare the power generated by the subsonic 747 airliner to a supersonic fighter like the F-4 Phantom II. In this example, the F-4 cruises at Mach 1.8 at 55,000 ft (16,765 m). The aircraft's two turbojet engines produce 11,560 lb (51,430 N) of thrust at its cruise speed of 1,742 ft/s (531 m/s). This combination of force and speed equates to a power of 36,620 hp (27,310 kW).

These examples illustrate how cumbersome it is to convert between thrust and power. However, you may be wondering why jet engines or rocket engines are rated in units of thrust but propeller-driven engines are rated in units of power. For example, the F119 turbofans used on the F-22 are rated at 35,000 lb (310 kN) of thrust each and one of the main liquid rocket engines of the Space Shuttle produces 418,000 lb (1,860 kN) at lift off. Meanwhile, a turboprop engine of a C-130 is rated at 4,508 hp (3,362 kW) and the piston engine of a Cessna 172 generates 180 hp (135 kW) of power. Why the distinction?

How a jet engine works

The answer relates to the fundamental way in which each of these engines works. Turbojet, turbofan, and rocket engines all work by directly accelerating a fluid to produce a thrust force, so it is most straightforward to rate these engines in terms of the size of that force. A piston engine, turboprop, or turboshaft is designed to perform mechanical work that turns a shaft. In other words, the engine creates a torque, and we saw earlier that one of the forms of the power equation relates power to the amount of torque created over time. The shaft that such an engine turns is connected to a propeller, which is an aerodynamic device that converts that power into thrust. The engine itself doesn't produce the thrust, but it turns a propeller that does. Also, two engines that generate the same power may not necessarily result in the same thrust since one may use a more efficient propeller than the other. For these reasons, it is more logical to rate these kinds of engines in terms of the power they create since that is the most direct quantity they produce.

How a turboprop or turboshaft engine works

Based on what we have seen, you ought to have a better appreciation for why it is preferable to compare jet engines in terms of thrust rather than power and propeller-driven engines in terms of power rather than thrust. While the opposite can be done, the process of converting between power and thrust requires us to know or assume additional information that is usually difficult or awkward to estimate.