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Discussion Starter #1 (Edited)
Well, here I am again. Wasting time to help you people I dearly love. It seems like a lot of people have no clue what the true meaning of a lot of car definitions are so I am going to type them all in one beautiful thread for your convenience.

*Note: Some of these definitions in which I understand but can not word to make you understand will be taken word for word out of the Lincoln Tech Automotive Division Automotive Technology text book. In which I have the right to use because I paid 23k for one year of school.*

Torque- A force that tends to rotate or turn things and is measured by the force applied and the distance traveled. The technically correct unit of measurement for torque is pounds per foot (lb-ft). An engine creates torque and uses it to rotate the crankshaft. The combustion of gasoline and air in the cylinder creates pressure against the top of a piston. That pressure creates a force on the piston and pushes it down. The force is transmitted from the piston to the connecting rod and from the connecting rod to the crankshaft. The engines crankshaft rotates with a torque that is transmitted through the drivetrain to turn the drive wheels of the vehicle.

Torque Multiplication- When gears with different numbers of teeth mesh, each rotates at a different speed and force. Torque is calculated by multiplying the force by the distance from the center of the shaft to the point where the force is exerted.

Power- Is a measurement for the rate, or speed, at which work is done

Horsepower- A rate at which torque is produced.
  • Example-An engine that produces 300 pound-feet of torque at 4,000 rpm produces 228 horsepower at 4,000 rpm. This is based on the formula that horsepower is equal to torque multiplied by engine speed and that sum divided by 5,252. The constant, 5,252, is used to convert the rpm for torque and horsepower into rpm's.
Wheel Horsepower- Based upon a lot of things, base horsepower, the loss of horsepower between moving parts, temperature, humidity, operation, dyno, altitude and other variables. That's why it is important to compare your own dynos to yourself. To not be discouraged if someone else got a higher wheel horsepower and you have more mods. Dynos should be used for your personal use in advancement through mods.

Volume- Is a measurement of size and is related to mass and weight. Volume is the amount of space occupied by an object in three dimensions: Length, width, and height.

Displacement- Is the volume of a cylinder between when the cylinders piston is at its lowest point of travel (BDC, Bottom Dead Center), and its highest point of travel (TDC, Top Dead Center). Displacement is usually measured in cubic inches, cubic centimeters, or liters.

Total Displacement- The sum of displacements for all cylinders in an engine. The total displacement of an engine (including all cylinders) is a rough indicator of its power output.
  • CID(Cubic Inch Displacement)=Pi(3.1416)x R^2(radius squared)x L(length of stroke)x N (number of cylinders)
Compression Ratio- Express' how much an engines air/fuel mixture will be compressed as the piston in a cylinder moves from BDC to TDC of the cylinder.

Gear- A toothed wheel that becomes a machine when it is meshed with another gear. Gears apply torque to other rotating parts of the drivetrain and are used to multiply torque.

Gear Ratio- An expression of gear size and tooth count of gears that are meshed together. The ratio reflects torque multiplication. To calculate a gear ratio, divide driven (output) by the drive (input).

Force- A push or pull and can be very large or very small.

Pressure- Is a force applied against an object and is measured in units of force per unit of surface area (PSI).

Speed- Is the distance an object travels in a set amount of time

Friction- A force that slows or prevents motion in two moving objects or surfaces that touch.

Current- Is the movement or flow of electricity. Current is measured in Amps.

Voltage- Is electrical pressure. Voltage is measure in Volts.

Resistance- Resistance is measure in Ohms

Ohms Law- V/AxR

Metric/USC Conversions- Take the first measurement then multiply it by the number next to it to get the measurement in the middle. Or you can reverse the problem if you have the oppistite measurement you want then multiply the number in the middle to the number next to it to get the measurement you understand.

Example- Converting Foot-pounds to Newton-meters
2 Foot-pounds x 1.3558=2.7116 Newton-meters
2 Newton-meters x .7376= 1.4752 Foot-pounds
  • Foot-pounds x 1.3558 = Newton-meters x .7376 = Foot-pounds
  • Horsepower x .7457 = Kilowatts x 1.341 = Horsepower
  • Inches x 25.4 = Millimeters x .03937 = Inches
  • Cubic Inches x .01639 = Liters x 61.024 = Cubic Inches
  • Pounds x .454 = Kilograms x 2.205 = Pounds
  • Miles Per Hour x 1.609 = Kilometers Per Hour x .6214 = MPH
  • Pounds Per Square Inch x .069 = Bar x 14.50 = PSI
  • Pounds Per Square Inch x 3.895 = kPa x .14503 = PSI
  • Fahrenheit-32 and then /1.8= Celsius x 1.8 + 32 = F
 

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Discussion Starter #6
NewbTuner said:
+1

Can you post the diff in all the horsepower measurments, ie. WHP,hhp etc.
i'll look it up tomorrow for you what each of them mean. Base HP, Brake HP, Hub HP, Wheel HP however there is no real calculation for the wheel HP.

Wheel horsepower is based upon a lot of things, base HP, the loss of hp between moving parts, temperature, humidity, operation, dyno, altitude. I'll add that to the post tomorrow morning.
 

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truflip said:
what is BDC and TDC?
Bottom Dead Center, Top Dead Center. This terms refer to the points of crankshaft rotation at which the piston is at the absolute bottom most point of travel and at the absolute topmost point of travel. The Dead Center part refers to the connecting rod being centered under the piston, i.e. completely vertical, not offset in either direction.
 

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good post, just one thing id like to elaborate on.

Horsepower- A rate at which torque is produced.
Example-An engine that produces 300 pound-feet of torque at 4,000 rpm produces 228 horsepower at 4,000 rpm. This is based on the formula that horsepower is equal to torque multiplied by engine speed and that sum divided by 5,252. The constant, 5,252, is used to convert the rpm for torque and horsepower into rpm's.
Torque is Work in a rotation, so if HP is the rate of Torque its also the rate of work, ie its not different than power.

it has been defined that a horse can do 33,000 ft-lbs of work in 1 minute. (this doesnt come from anywhere, just somebody a long time said they think this is what a horse can do) since the Torque is a rotational force, to get the distance multiplier we need to factor out 2pi (since 2 x pi x r = the distance around a circle) so 33000/(2x3.1415) = 5252 and thats where 5252 comes from in case anyone was wondering.
 

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Can you please read my thread in the mechanical problem forum(car broke down)?????Any suggestions would be great....

Good luck on the job.......:thumb:
 

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I'll post several links and quotes. This is not my .02 but simple math. Pictures will follow later today. Makes it easy to see and understand with the pics!

Horsepower and Torque - Craig's Website at Backfire.ca

Torque​

Torque is a force that tends to cause a rotation. A force applied at a non-zero distance from an object's centre will tend to rotate the object. This is easily seen in real life. If you put a wrench on a bolt and pull on the end of the wrench, the bolt will turn. If you apply the same pulling force directly on the bolt, it will not turn, because the force is not distant from the object's centre. The amount of torque is determined by multiplying the magnitude of the force by the force's distance from centre.

Work​

Work is something that is not talked about much when talking about cars. Work is defined as the transfer of energy from one system to another, such as a person pushing a box across a floor. Mathematically, work is a force times a distance, and has units such as foot-pounds or Newton-metres. The direction of force (or at least a component of it) must match the direction of motion for the force to be considered to be doing work.

The force is doing work on the object, because it is causing the object to move along a distance.



Difference Between Torque and Work​

Notice that the units for torque and work are basically the same, yet torque and work are two different things. Torque is a force that causes a rotation, which means that it does not actually cause an object to move along a distance. Therefore, torque is not work.



The difference between torque and work.​

On a rotating shaft, the work is done by the torque. This is because torque is a force about a circle, and the shaft is a circle. The force is going round and round, and so is the shaft, so if we "unroll" the shaft, we have a force traveling across a linear distance. That's work.

On a rotating shaft, the torque is doing the work.

Power​
not horsepower but Power.

Power is the amount of work that can be done in a certain amount of time, or "the rate of work", or "the rate of energy transfer between systems". Therefore, the units for power are in the form below:



Power is always a force multiplied by a distance over a period of time.

The above equation can be rewritten in terms of force and speed, as seen below:

Using the definition of speed, power can be expressed in terms of force and speed.




Shaft Power​

On a rotating shaft (like an axle), the torque is doing the work, and the shaft's rotational speed is time-dependent, so shaft power is the product of its rotational speed and its torque. Using arbitrary units, the power formula for a rotating shaft is:


Shaft power using arbitrary units.
 

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Units of Shaft Power​

When using pound-feet as units of torque, revolutions per minute (RPM) for shaft speed, and horsepower for power, shaft power can be expressed with the following formula:


Shaft power in horsepower.

The above power formula is often misinterpreted as showing that power and torque are the same thing, or that they somehow trade hands with each other at 5252RPM. This mistake is from the fact that a graph of torque in pound-feet and power in horsepower versus engine RPM has crossing lines at 5252RPM. Torque and power play the same role whether the engine is revving below, at, or above 5252RPM. Many diesel engines, and even some gas engines, are not even capable of revving that high at all.
The above statements can be proven by changing the units for power and torque. Let's use kilowatts for power, and Newton-metres for torque, just like the Aussies do. With that, we get:


Shaft power when using metric units.

The constant used for calculation is now 9549, not 5252 like it was when we were using pound-feet and horsepower. This means that a graph of power and torque versus revs using metric units would have crossing curves at 9549RPM instead of 5252RPM. :coffee:
 

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Gears

Gears are used to change the torque and rotational speed of a part of a system of rotating shafts, or to change the direction of the transmitted motion. An example of the former would be the car's transmission, while an example of the latter would be the rear axle gears.
An ideal (lossless) gear set transmits an equal amount of power to the output shaft as it received from the input shaft. This means that if a gearbox has a 2:1 gear ratio, the output shaft will be rotating half as fast as the input shaft, but will have double the torque. Below is a drawing that shows the effects of a gear set, using an abitrary ratio, GR.



The gearbox is given a certain amount of power (from the engine), in the form of torque and revs (tq x revs = hp). It then puts out an equal amount of power, with the revs and torque adjusted according to the gear ratio.

Formulae used for gears.




Drivetrain Gearing​

A car's drivetrain uses multiple sets of gears to control how much of the engine's total power is going to torque, and how much is going to rotating the wheels.

All gasoline piston engines produce too little torque and too many revs to properly turn the wheels. With 27 inch tires (13.5" radius), 6000RPM at the wheels is 450mph! It also takes a lot more than a few hundred pounds of force to even move something as heavy as a passenger car. This is why all cars have drivetrains that divide the revs and multiply the torque. (divide revs portion is what the high rev Honda engines do best it is how they can make a 130ft'lb of torque Si compete with turbochaged 250ftlbs from the GTI. :vtec:)

To accomplish this, most cars are fitted with two sets of gearing between the engine and the wheels. The first set is the transmission, which multiplies the torque a certain amount, depending on what gear it is in. Typically, first gear has a ratio near 3:1, while the top gear has a ratio near 0.8:1. After the transmission, there is another set of gears which usually have a ratio of around 2.5:1 through 4.8:1, depending on the vehicle. Below is a diagram of a typical drivetrain found in most cars:


The drivetrain of a car is fitted with a transmission and final drive gearing to adjust the engine's torque and revs to accelerate the car.



The wheel torque and revs vary with the engine torque and revs, and the gear ratios in between.



The reason that cars have transmissions with multiple gears is so that the engine can be kept within its operating rev range (which is why a good flat torque curve is great) while the vehicle accelerates from rest to possibly over 200mph. In first gear, there is plenty of acceleration because of the torque multiplication, but very little speed before the engine hits its redline. In second gear, there is slightly less acceleration, but a slightly higher top speed before hitting the redline. This trend continues through each gear in the transmission.

The combination of speed and acceleration is related to the power available (not HP but power as described above that reaches the ground).

 

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Accelerating a Car​

Newton's second law of motion states that the acceleration of a body is related to the force being applied and the mass of the body, as seen below:

Newton's second law of motion. A greater force or a lower mass will result in a greater acceleration.


In order for there to be any acceleration, the force must be applied at the same speed that the object is traveling, for a non-zero length of time. A force being applied at a certain speed for a period of time is power, therefore, the acceleration force on a moving object is determined by the power being applied at that speed.

The wheels receive torque and rotational speed from the engine, and lay down a force onto the pavement. It is this force which accelerates the vehicle. The car's speed is determined by the rotational speed of the wheel.


The acceleration of a moving car is equal to the power divided by the speed and the mass. The product of speed and mass is known as momentum.

The acceleration force of a car comes from the torque at the wheels. This is why the acceleration is often calculated from engine torque by using the large formula seen below:


The acceleration force can be calculated by passing the engine torque through the entire drivetrain to the road.




The acceleration force can be calculated by passing the engine torque through the entire drivetrain to the road.



If the speed of a car and the power of its engine is known at a given instant, the force of acceleration can be calculated without knowing anything about the drivetrain gearing, tire diameter, or even the engine torque, as demonstrated below using imperial units:

When the power and speed are known, the acceleration force can be calculated directly without knowing anything about the drivetrain.



The torque method and the power method will both produce the same results, as seen in the example below.



The calculated acceleration force is the same when using the torque method or the power method.
 
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