Horsepower VS Torque

[XLR8]

;help Ok all you gearheads (and I use the term with the greatest respect), here's your chance to educate a novice and help a girl out.

As my understanding is very limited, I am not even clear on how to phrase my question so please keep that in mind and limit the flaming. I'm really going to display my ignorance here.

I've read lots of posts which refer to horsepower and torque and I am interested in learning more about both and their relation to each other and performance. I seem to recall the basic concept that HP is the power of said number of horses to do a certain amount of work, but I haven't a clue about torque. Is torque the force applied to turn the wheels? And is the drive shaft the means of delivering that torque (force)? So how does one know what torque their car produces? I know that my 1998 convertible has an LS1 345 HP engine, but what about torque? I also know that horsepower can be increased through modifications, so can the same be said for torque? I've also seen the abbreviation RWHP and take it this means rear wheel horsepower - what's the difference?

Enough with the questions already! Sorry guys, but as you can see I'm totally ignorant on the subject. Any info and even links to places I can read up on the subject would be much appreciated.

Thanks in advance...
JAG

 

[Bioscache2]

;help Ok all you gearheads (and I use the term with the greatest respect), here's your chance to educate a novice and help a girl out.

As my understanding is very limited, I am not even clear on how to phrase my question so please keep that in mind and limit the flaming. I'm really going to display my ignorance here.

No worries, everyone has to ask the question sometimes. I'll start from the top and work down.

I've read lots of posts which refer to horsepower and torque and I am interested in learning more about both and their relation to each other and performance. I seem to recall the basic concept that HP is the power of said number of horses to do a certain amount of work, but I haven't a clue about torque. Is torque the force applied to turn the wheels?

You are correct that torque is a measure of force. Most torque numbers from a car have to do with the force present at the crank or engine. Torque is measured in ft-lbs. Your vette will produce 450 ft-lbs. This is eqivalent to the amount of turning force that is present if you get a rod that is 1 foot long and put 450 lbs on it in the downward motion You multiply the length by the force to get ft-lbs. So the same amount of force is applied if you got a 2 foot rod and put 225 lbs on the end (2*225=450). Thats torque. Horsepower is measure of force applied of time. For example if the engine turns over 1000 times in a minute, a certain amount of power is produced in that time. If you increase the engine speed you increase your power (generally, not always) since now you are applying the force of turning, more often. HP = (Torque * RPM)/5252.
Now torque and HP vary at different RPM's (has to do with air filling effciencies, but thats the advanced course). 450 is the max but that only comes at a certain RPM. The higher RPM it comes at, the more horsepower the car produces (see equation). Torque is the feeling that throws you in the back of the seat but Horsepower produces high speed.
You can go here for a bigger explanation http://vettenet.org/torquehp.html

And is the drive shaft the means of delivering that torque (force)? So how does one know what torque their car produces? I know that my 1998 convertible has an LS1 345 HP engine, but what about torque? I also know that horsepower can be increased through modifications, so can the same be said for torque? I've also seen the abbreviation RWHP and take it this means rear wheel horsepower - what's the difference?

The drive shaft is part of what delivers the torque. All the pieces do, transmission, drive shaft, differential, etc. These pieces aren't perfect and some of the force is lost due to friction so the force created at the engine isn't what is applied to the wheels. A conservative estimation is you lose 15% of what is at the crank (engine) for both engine and torque. So RWHP is what is present at the wheels, it is also the reading you will get from a dyno.
As for modifications, they do generally affect both HP and Torque. Most of the time they increase it but sometimes they just alter the RPM's it is produced at (remember if the max torque comes at a higher RPM than you have more horsepower). Modification may also help "flatten the line." This means instead of producing lots of torque at one RPM and low torque elsewhere you get high torque at more RPM's. This is ideal. (You wouldn't want to have to rev your engine real high just to move right). Well I think I've covered everything you've asked. If theres anything else you're wondering about feel free to ask.

Enough with the questions already! Sorry guys, but as you can see I'm totally ignorant on the subject. Any info and even links to places I can read up on the subject would be much appreciated.

Thanks in advance...
JAG

 

[RJS91RGTP]

Torque vs Horsepower

Hello XLR8, I saw your question and can provide only the basic answer to you but I am sure more responses will come from those techies that can really explain it. The short answer to your long question is that Torque is what gets you off the starting line quickly, makes your head snap back when you jump on the gas. Torque gets you going from 0-60 mph fast!! Horsepower is what keeps you going and gets your Vette to top speed and can keep it there. They usually go hand in hand, more HP gets you more torque if done properly. I hope this helps as it is just a simple answer. I suspect the torque on your 345 HP engine is about 340 foot pounds. I have an 02 coupe that has 350 HP and 350 foot pounds of torque.

RJ - Suburban Chicago

 

[Ken]

It was just about a year ago that I once again brought the subject of horsepower and torque to the table: Something new re: Horsepower vs. Torque.

 

[XLR8]

Bioscache2 and RJS91RGTP (and Ken too I see as writing this response) - thanks for sharing your time and knowledge with me.

Gotta love that G force! And the simple answer was appreciated just as much as the more in depth explanation.

HP = (Torque * RPM)/5252

Where does the 5252 figure come from in the equation? Is this the RPM at which the stock LS1 produces maximum HP and torque or am I off base in that assumption?

If you increase the engine speed you increase your power (generally, not always) since now you are applying the force of turning, more often.

This would explain why I've seen statements by other owners, mostly in their signatures, that their cars have X HP at 5000 rpm or X torque at 5000 rpm.

Thanks for the invitation to post more questions. I'll read up on the links you all have supplied and undertake some self study.

 

[Ken]

Where does the 5252 figure come from in the equation?

From epi-eng.com:

"OK, where does the 5252 come from?"

Here is the answer.

By definition,

POWER = FORCE x DISTANCE ÷ TIME​

Using the example above where a constant tangential force of 100 pounds was applied to the rotating handle at a 12" radius, we know the force, so to calculate power, we need the distance the handle travels per unit time.

Power = 100 pounds x distance per minute​

OK, how far does the crank handle move in one minute? First, determine the distance it moves in one revolution:​

DISTANCE per revolution = 2 x p x radius​

DISTANCE = 2 x 3.1416 x 1 ft = 6.283 ft. per revolution.​

Now we know how far the crank moves in one revolution. How far does the crank move in one minute?​

DISTANCE per min. = 6.283 ft .per rev. x 60 rev. per min. = 377 feet per minute​

Now we know enough to calculate the power, defined as:​

POWER = FORCE x DISTANCE ÷ TIME​

so

Power = 100 lb x 377 ft. per minute = 37,700 ft-lb per minute​

Swell, but how about HORSEPOWER?

Remember that one HORSEPOWER is defined as 33000 foot-pounds of work per minute.

Therefore,

HP = POWER (ft-lb per min) ÷ 33,000​

So the power being applied to the crank-wheel above is: 37,700 ft-lb per minute, or 1.14 HP (37,700 ÷ 33,000).

Now we combine some stuff we already know to produce the magic 5252.

We already know that TORQUE = FORCE x RADIUS.​

If we divide both sides by RADIUS, we get:

FORCE = TORQUE ÷ RADIUS (a)​

Now, if DISTANCE per revolution = RADIUS x 2 x p​

then​

DISTANCE per minute = RADIUS x 2 x p x RPM (b)​

We already know POWER = FORCE x DISTANCE per minute (c) so if we plug the equivalent for FORCE from (a) and distance per minute from (b) into (c), we get:​

POWER = (TORQUE ÷ RADIUS) x (RPM x RADIUS x 2 x p)​

Dividing both sides by 33,000 to find HP,

HP = TORQUE ÷ RADIUS x RPM x RADIUS x 2 x p ÷ 33,000​

By reducing, we get

HP = TORQUE x RPM x 6.28 ÷ 33,000​

Since

6.2832 ÷ 33000 = 1 ÷ 5252​

therefore

HP = TORQUE x RPM ÷ 5252​

Note that at 5252 RPM, torque and HP are equal. At any RPM below 5252, the value of torque is greater than the value of HP; Above 5252 RPM, the value of torque is less than the value of HP.