Serious Question

[Bazza-old]

can someone explain bhp

how and what is measured?

flywheel/wheels

[wildrnes]

How Horsepower Works

by Marshall Brain

› Introduction to How Horsepower Works

› Definition

› Measuring Horsepower

› Horsepower in High-Performance Cars

› Lots More Information

› Shop or Compare Prices

Definition

The term horsepower was invented by the engineer James Watt. Watt lived from 1736 to 1819 and is most famous for his work on improving the performance of steam engines. We are also reminded of him every day when we talk about 60-watt light bulbs.

The story goes that Watt was working with ponies lifting coal at a coal mine, and he wanted a way to talk about the power available from one of these animals. He found that, on average, a mine pony could do 22,000 foot-pounds of work in a minute. He then increased that number by 50 percent and pegged the measurement of horsepower at 33,000 foot-pounds of work in one minute. It is that arbitrary unit of measure that has made its way down through the centuries and now appears on your car, your lawn mower, your chain saw and even in some cases your vacuum cleaner!

Measuring Horsepower

If you want to know the horsepower of an engine, you hook the engine up to a dynamometer. A dynamometer places a load on the engine and measures the amount of power that the engine can produce against the load.

Torque

Imagine that you have a big socket wrench with a 2-foot-long handle on it, and you apply 50 pounds of force to that 2-foot handle. What you are doing is applying a torque, or turning force, of 100 pound-feet (50 pounds to a 2-foot-long handle) to the bolt. You could get the same 100 pound-feet of torque by applying 1 pound of force to the end of a 100-foot handle or 100 pounds of force to a 1-foot handle.

Similarly, if you attach a shaft to an engine, the engine can apply torque to the shaft. A dynamometer measures this torque. You can easily convert torque to horsepower by multiplying torque by rpm/5,252.

You can get an idea of how a dynamometer works in the following way: Imagine that you turn on a car engine, put it in neutral and floor it. The engine would run so fast it would explode. That's no good, so on a dynamometer you apply a load to the floored engine and measure the load the engine can handle at different engine speeds. You might hook an engine to a dynamometer, floor it and use the dynamometer to apply enough of a load to the engine to keep it at, say, 7,000 rpm. You record how much load the engine can handle. Then you apply additional load to knock the engine speed down to 6,500 rpm and record the load there. Then you apply additional load to get it down to 6,000 rpm, and so on. You can do the same thing starting down at 500 or 1,000 rpm and working your way up. What dynamometers actually measure is torque (in pound-feet), and to convert torque to horsepower you simply multiply torque by rpm/5,252.

If you plot the horsepower versus the rpm values for the engine, what you end up with is a horsepower curve for the engine. A typical horsepower curve for a high-performance engine might look like this (this happens to be the curve for the 300-horsepower engine in the Mitsubishi 3000 bi-turbo):

What a graph like this points out is that any engine has a peak horsepower -- an rpm value at which the power available from the engine is at its maximum. An engine also has a peak torque at a specific rpm. You will often see this expressed in a brochure or a review in a magazine as "320 HP @ 6500 rpm, 290 lb-ft torque @ 5000 rpm" (the figures for the 1999 Shelby Series 1). When people say an engine has "lots of low-end torque," what they mean is that the peak torque occurs at a fairly low rpm value, like 2,000 or 3,000 rpm.

Another thing you can see from a car's horsepower curve is the place where the engine has maximum power. When you are trying to accelerate quickly, you want to try to keep the engine close to its maximum horsepower point on the curve. That is why you often downshift to accelerate -- by downshifting, you increase engine rpm, which typically moves you closer to the peak horsepower point on the curve. If you want to "launch" your car from a traffic light, you would typically rev the engine to get the engine right at its peak horsepower rpm and then release the clutch to dump maximum power to the tires.

Horsepower in High-Performance Cars

A car is considered to be "high performance" if it has a lot of power relative to the weight of the car. This makes sense -- the more weight you have, the more power it takes to accelerate it. For a given amount of power you want to minimize the weight in order to maximize the acceleration.

The following table shows you the horsepower and weight for several high-performance cars (and one low-performance car for comparison). In the chart you can see the peak horsepower, the weight of the car, the power-to-weight ratio (horsepower divided by the weight), the number of seconds the car takes to accelerate from zero to 60 mph, and the price.

Horsepower Weight (lbs) Power:Weight 0-60 mph (seconds) Price

Dodge Viper 450 3,320 0.136 4.1 $66,000

Ferrari 355 F1 375 2,975 0.126 4.6 $134,000

Shelby Series 1 320 2,650 0.121 4.4 $108,000

Lotus Esprit V8 350 3,045 0.115 4.4 $83,000

Chevrolet Corvette 345 3,245 0.106 4.8 $42,000

Porsche Carrera 300 2,900 0.103 5.0 $70,000

Mitsubishi 3000GT bi-turbo 320 3,740 0.086 5.8 $45,000

Ford Escort 110 2,470 0.045 10.9 $12,000

You can see a very definite correlation between the power-to-weight ratio and the 0-to-60 time -- in most cases, a higher ratio indicates a quicker car. Interestingly, there is less of a correlation between speed and price. The Viper actually looks like a pretty good value on this particular table!

If you want a fast car, you want a good power-to-weight ratio. You want lots of power and minimal weight. So the first place to start is by cleaning out your trunk!

took me ages to type that

[Monster-Mat]

Horse power \Horse" pow`er\

1. The power which a horse exerts.

2. (Mach.) A unit of power, used in stating the power

required to drive machinery, and in estimating the

capabilities of animals or steam engines and other prime

movers for doing work. It is the power required for the

performance of work at the rate of 33,000 English units of

work per minute; hence, it is the power that must be

exerted in lifting 33,000 pounds at the rate of one foot

per minute, or 550 pounds at the rate of one foot per

second, or 55 pounds at the rate of ten feet per second,

etc.

Note: The power of a draught horse, of average strength,

working eight hours per day, is about four fifths of a

standard horse power.

Brake horse power, the net effective power of a prime

mover, as a steam engine, water wheel, etc., in horse

powers, as shown by a friction brake. See Friction

brake, under Friction.

Indicated horse power, the power exerted in the cylinder of

an engine, stated in horse powers, estimated from the

diameter and speed of the piston, and the mean effective

pressure upon it as shown by an indicator. See

Indicator.

Nominal horse power (Steam Engine), a term still sometimes

used in England to express certain proportions of

cylinder, but having no value as a standard of

measurement.

3. A machine worked by a horse, for driving other machinery;

a horse motor.

[Bazza-old]

thank you mat

what about the values of fly wheel against wheel ??????????????????

jees took me ages to think that question up :duh:

[Monster-Mat]

)RPM stands for Revolutions Per Minute. It is the number of times the engine crank-shaft turns in ONE minute.

2)Torque is the turning force which turns the crank-shaft of the engine. It is measured in units of Kilogram-Metres, usually written as KgM. ONE KgM is the turning (or bending) force exerted by a force of ONE kilogram acting on the free end of a bar of length ONE metre, the other end of which is held rigidly. Suppose, the length of your arm from shoulder to palm is ONE metre and you are holding a weight of one kg. in your palm with your arm fully extended horizontally (parallel to the ground), then the torque which this one Kg. weight is producing at your shoulder is ONE KgM.

3)Now, understand that ONE Horsepower (Metric) is defined as the POWER required to lift 75 kilograms of weight by ONE metre in ONE second. (Which would be mathematically the same as the POWER to lift ONE kilogram of weight by 75 metres in ONE second. This METRIC horsepower is correctly written at PS (a German abbreviation meaning Pferd Stark) and not BHP. Though they both mean the same thing (i.e. Brake Horse Power), the term PS is used to distinguish it from BHP because earlier (when we used the British system) BHP used to mean British Horse Power. Now (since Bharat Sarkar has adopted Metric System by Law), even where you see the word BHP, it means Brake Horse Power and NOT British HP.

The way to calculate BHP is by the formula BHP=

(2 x pye x Revs.Per Second x Torque) divided by 75.

Since turning (revolutions) of the engine (crank-shaft) is usually measured in Revolutions Per Minute (RPM), and there are 60 seconds in one minute,

Therefore RPM=Revs.Per Second x 60. BHP=(2 x pye x Revs.Per Sec. x 60 x Torque) divided by 75x60.

which is the same as BHP=(2 x pye x RPM x T) divided by 4500 (because 60x75=4500).

Now 2 is the number 2 pye=22/7 (22 upon 7) RPM=say N revs. per minute Torque=T (unit of torque is Kilogram-Metre, written as KgM)

Thus BHP=(2 x pye x N x T) divided by 4500. As you can see, in the above formula, the numbers 2, 22/7 and 4500 are pure numbers which will not (cannot) change for any engine. Only N and T will (can) change.

Thus you can see that for two cars having same BHP but different RPM, the Torque will have to be different.

Now Bazza for the different values you need to know the losses that are found in transmissions.......hope this helps