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I have always wondered what is the difference between Horse Power and Torque. :-?

What do each mean?
What do each do for the car?
Better to have more HP, or more Torque?

Just for an example.....
No flames please but I have a R/T Dakota StdCab with 250HP, and 350 Torque (5.9 Liter 360ci). I have this to tide me over till I get a Z06. What do thoes numbers say about the truck. It also has a 392 auto rear end.
http://home1.gte.net/res0aae8/rtdakota/rtdakota.html

Thanks
Z49Z06
 

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I cheated and found this through an internet search. :lol:

HORSEPOWER

Horsepower is a measure of the work an engine can do. The word "horsepower" was coined by James Watt, an engineer from Scotland who compared the work of his invention, the steam engine, to that of a horse. Watt wanted to know how many horses his steam engine would replace. He found that a robust horse could lift a 150-pound weight 220 feet in the air (using a pulley system) in 60 seconds. This measurement of work became the standard we still use today. More precisely, horsepower is the force needed to move a specific amount of weight a specific distance in a specific amount of time. Two key words come into play here: "work" and "power." Work is the amount of force than can be applied over a specific distance (WORK = FORCE x DISTANCE). Power is a measurement of the time it takes to accomplish the work. An understanding of the word "horsepower" hinges on grasping the literal meaning of these two words.

Visualize a man pushing his 4x4 off the trail after completely torching his overburdened alternator. The man has to push his 6,000-pound truck on 44-inch Gumbo Monster Mudders (force) 15 feet (distance) to get it off the road. If the man succeeds all by himself, he will have accomplished 9,000 lb-ft of work. On the other hand, he won't have done any work, no matter how hard he tries, if the truck doesn't budge. The only thing that would make his job easier is if he had the power to push his rig off the trial in 10 seconds rather than 30 seconds. More physical power, in combination with his work effort, is needed move the truck more quickly. Whether he moves the truck in 10 seconds or 30 seconds, the man will have done the same amount of work.

HORSEPOWER = TORQUE x RPM/5,252

TORQUE

Think "twisting force" when you consider the word torque. It differs from "work" in that torque is a measure of force that produces rotation or twisting action around an axis. In essence, torque is twisting force. Torque is the product of the force, measured in pounds, and a radius perpendicular to the axis of the force extending to the point where the force originates, measured in feet. This resulting figure is expressed in pounds-feet, or lb-ft. As an object rotates around a given point (the axis), the speed of its rotation depends on both the applied force (the twisting force) and the torque arm (or moment arm). The torque arm represents the distance from the point of rotation to the point where the force is applied. Torque, then, is the product of the force and the torque arm.

You apply torque every time you affix a wrench to the head of a bolt and turn it. When you place that wrench on a bolt head, you're going to hang onto the wrench handle with all 200 pounds of your body weight. If the wrench is two feet (the wrench handle acts as the torque arm) in length, the mathematical expression would be: 2(distance) x 200 pounds (force applied) = 400 lb-ft (torque). Another way to look at it is to visualize a rope wrapped around a drum with a 1-foot radius. If the rope were to be pulled with 550 pounds of force, the torque would equal 550 lb-ft.

TOQUE = DISTANCE x WEIGHT
 

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Thanks for the info Frank, that was helpful!

Z40 Z06, sweet truck, I always liked the looks of those Dodge R/T's.

Paul
 

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Here some real world equations using torque. You should be able to calculated the acceleration of your car using it.

Newton has an equation F = ma

Some Greek Palto? had this equation

Torque = F * lenght

Think of a torque wrench. You put 10 pounds of force at the end of a 1 foot long wrench and you create 10 foot - lbs of torque.

OK for a little Alegbra if F = ma and Torque = F * lenght then you can solve for a (acceleration) with torque.


So you have an equation a = Torque/(lenght*m)

So if you know your car's weight (m) and the torque at the rear wheels and the radius of the rear wheel you can calculate the acceleration.

There is one little thing to remember is that gear ratios are multiplers on torque.

If this make sense I can show an example calculation using a 2002 Z06 in first at 400 lbs - of torque.
 

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Just give me a BIG FAT torque sandwich anyday:D
:cheers:
 

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As someone quoted here before me:

Horsepower is measured by how fast you hit the wall.

Torque is measured by how far the wall moves. :D
 

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OK here is the acceleration that is on the car at 4800 RPM, which is when 400 ft-lbs of torque are produce.

The gear ratios multiply the torque from the flywheel. So the torque is 400- ft-lbs at the flywheel. After first gear and before the rear end the torque is 400 ft ?lbs * 2.97 (first gear ratio) 1188 ft-lbs of torque. Then at the axle after the rear end gear ratio 1188 ft-lbs and 3.42 (rear end gear ratio) 3606 ft-lbs of torque. However you have drive line loss due to friction. 14% is a good figure. So the torque is about 3101 ft-lbs.

Now to get the force at the ground. F = Torque / Length of moment arm. The moment arm is the radius of the wheel (rim plus tire side wall). The moment arm is 1.09 ft. So the force is 3101 ft-lbs / 1.09 ft or 2844 lbs of force.

Using Newton?s equation a = f/m 2844 lbf/ (3115 lb car + 185 lb driver) you have an acceleration of .86 g?s or 27.7 ft/sec2. Man that is a lot of acceleration. You can see why weight is so important when you want a car to accelerate faster.

I would like to add that peak torque at a RPM and peak horsepower at a RPM tells a little about the car. But when you have a torque curve vs RPM or Hp vs RPM curve you know a lot. Remember from one you can calculate the other. And for all the vehicle dynamics calculations you need to have a Force.

Makes sense?

There is a bunch of other stuff that is behind all these calculations. I recommend a book Fundamentals of Vehicle Dynamics written by Thomas D. Gillespie. It is published by SAE. It is packed with all the equations an Automotive Engineer needs to do analysis on a vehicles dynamics.
 

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Forgot to comment to Frank

I cheated and found this through an internet search
You may have cheated but it is a great explaination :cheers:

I find a lot of times people get very confused on all this physics and it really is pretty simple if the explaination is ever day common sense. In fact I find most folks really have a hard time understanding this subject fully.

I am going to make a dig at some of my professors I had in college. Been a long time ago so most are to old to care. Always found that those who explained the material in every day common sense examples understood the material cold.
 

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TX02Z06 - very eloquent!

Drag race machines thrive on HP because time is critical (more work per unit of time). Real drag engines always operate above peak torque (highest volumetric efficency and the 5252 in the equation). Get the needed torque with gears.
 

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Roger,

I see from your profile that you are an Aero head. Which company do you work for?
 

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TX02Z06 said:
Roger,

I see from your profile that you are an Aero head. Which company do you work for?
Spent my career in power systems (fuel, hydraulics, propulsion) and testing of high perf military aircraft (F-4, F-15, AV-8, F/A-18) for McDonnell - now Boeing. They were so appreciative they send me a check every month.
 

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To me the hp v. torque thing is a lot like electricity. Very few people understand it and even fewer need to. The most important thing to know about hp and torque is a little more is a little better and a lot more is a lot better. It's that simple. :D
 

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Based on my experience testing heavy duty diesel engines in the Engineering Laboratory, we use this mathematical formula to measure hp:

Torque x engine RPM, divided by 5250.

The 5,250 value is a constant used in the calculation.

Of course, with today's computer controlled dynamometer testing, HP, torque, and dozens of other engine operating parameters are monitored and recorded instantly on computer files.

Zippy :z: :z:
 

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Roger Ramjet said:


Spent my career in power systems (fuel, hydraulics, propulsion) and testing of high perf military aircraft (F-4, F-15, AV-8, F/A-18) for McDonnell - now Boeing. They were so appreciative they send me a check every month.
Hey Roger!

I helped build the first seven pre-contract F-18s from the cockpit back back in 78-79 at No Throw Up Air Crash Company in Long Beach! :lol: :lol: :lol:

Started out structural installer, because I was big enough to drill holes through titanium and pound titanium rivets. Ended up putting the ECS up in the porkchop and air-brake hydraulics.

As an extra aside, my wife started working for McDonnell Douglas back in 93. She's a Boeing "wienie" now! I think a lot of those folks still resent the Boeing "bug" just a bit.:lol:

Small world isn't it?

Take care,

Dan Farmer
 

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Spent my career in power systems (fuel, hydraulics, propulsion) and testing of high perf military aircraft (F-4, F-15, AV-8, F/A-18) for McDonnell - now Boeing. They were so appreciative they send me a check every month.
Have to say that is great!!! Sounds like you had a great Career at Mac Air.

My wife was a hydraulics engineer on F-22. She has moved on to System Engineering for better or worst. I am doing Flight Control design.


Dan;
I almost when to work for Douglas in 1978 in the propulsion group, ended up at Boeing, then Lockheed, then Northrup, then Lockheed, then General Dynamics, which Lockheed purchased and then merged with Martin. The amazing thing with all the moving around is I have 21 years of service at Lockheed Martin. Aerospace what a business!!!!
 

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By TX02Z06:
There is a bunch of other stuff that is behind all these calculations. I recommend a book Fundamentals of Vehicle Dynamics written by Thomas D. Gillespie. It is published by SAE. It is packed with all the equations an Automotive Engineer needs to do analysis on a vehicles dynamics.
Thanks for the tip! I ordered it from Amazon.
 

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Really quick explanation: engine output power determines acceleration, engine torque has nothing to do with it.

To maximize acceleration, you maximize engine power output at any given time. With a CVT you would run the engine at its power peak to get the best 0-60, 1/4 mile, etc.

Going back to wrench example, it will take a certain amount of torque to break a bolt loose (overcome the friction/stiction/and other forces), but the power used will determine how fast you can run it out of the hole.

Search google for 'horsepower torque acceleration' and you can find some decent articles on explaining the principles of horsepower and torque.

I tried to keep this short and sweet but can rant for quite some time if provoked ;-)
 
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