You've finally said something that I can illustrate why I am correct. That statement, is 100% untrue. Torque does not move anything unless it has RPM...put the two together and you've got movement. Ironically, putting torque and RPM together....gives you horsepower!

Again, completely untrue.

A vehicle couldn't have 1000 hp if it didn't have torque (and lots of it). What gave you that 1000 horsepower, is lots of torque and lots of RPM.

Also, if you had 1000 ft-lbs of torque....great....but how is it going to spin w/o RPM? RPM and torque...combine into horsepower...

Don't you get it? Horsepower IS made up of torque and RPM....without either....you have no horsepower.

If you have 1000 ft-lbs of torque....you can't move without RPM......put it all together and you get horsepower dude.


Again, torque by itself doesn't move anything....what moves you is the torque and RPM. The horsepower is a combination of torque (power) and RPM (movement/speed)....

 

If horsepower is a function of torque how could one possibly build an engine without horsepower? I have a few of those engines - they are in parked vehicles!

This thread has gotten confusing. Torque is a twisting force, the POWER of the driveshaft. Horespower is a function of torque and RPM as has been pointed out here. Without torque there is no HP. Horsepower is the SPEED (acceleration) that the driveshaft moves. Watch a big truck when you are parked next to it - watch how slowly the driveshaft moves as the engine moves that amount of weight (Torque). Try watching the driveshaft on a floored Corvette - it will immediately spin too fast for you to see (HP).

 

TRUE

This is not true. Horsepower is NOT the speed that the driveshaft moves. I hope I don't offend you but, that driveshaft example just simply says nothing.

I was trying to make this as simple as I could and you're right, all it did was get confusing.


Horsepower is a number representing the relationship between torque and RPM.

Horsepower is related to acceleration.

Torque is ONLY how much twisting force an engine can produce. THATS IT, that's all there is to torque.

Horsepower is the confusing one. You're all confused.

 

No, I actually DO get it now after you've explained (patiently) but have a hard time explaining my thought. The driveshaft example is bad I admit. I'll just have to be satisfied that I finally get it now...

 

Horsepower is a very difficult concept to understand.....most people....don't have a clue. Most people on this board, don't have a clue. They've never really examined and analysed it.


My best suggestion is to just read the posts I've made here. It may take a couple times but what I've said will make sense to you, and if something I've said doesn't make sense to you...then ask me...I'll clarify...

Time for me to eat dinner!

 

Yall should read this page:

http://www.musclecarclub.com/library...ne-terms.shtml

 

Some interesting technical information on the way a conventional Otto engine generates HP and torque, looking at it mostly from a piston-to-crank perspective, can be found here: Physics In an Automotive Engine

 

"That high horsepower/low torque snowmobile engine pushing 700 lbs can accelerate very quickly. Load that engine up with another 2000 lbs, forget it...the acceleration would be drastically lowered"

- thats what i was saying.

 

MustangGT221-I misinterpreted what you said. My mistake, it sounded like you were trying to say that horsepower is the key factor in acceleration, and that torque didnt matter. After reading your other posts, I see you do have a pretty good grasp on it, and you said basically what I was trying to say in the beginning, lol.
Silver Streak's physics makes sense, but he is missing the message that MustangGT221 was trying to send.

 

I'm not exactly sure hoe it works but all i know is more torque means more power and when i pull i just want to know if it has enough to do the job horsepower is just a bonus. and oh yeah stop signs are over rated......like brakes

 

Ah, but to define HP and torque, one must use physics.

Torque is rotational force, and does determine acceleration, due to F = ma (Force equals mass times acceleration). For a given truck, we can measure its mass, and then whatever pedal you give it determines how much torque up to the engine's max torque. That torque moves through the driveline, resulting in a horizontal force where the rubber meets the ground. That is what accelerates the truck. As long as there is a net force in one direction, there will be acceleration. Once the wind resistance equals the force the tires are applying, constant speed is achieved. For a constant torque, if you increase mass, acceleration must decrease.

Horsepower is a measure of the rate at which work is being done. (Look at the metric equivalent--watts). Work is horsepower times time. Or, 1 hp = 550 ft*lb/sec = 746 W. And, horsepower is determined by measuring torque and RPM, then calculating, as others have stated, or by measuring the work done by the engine (i.e., moving a 5000lb. truck 1 mile at top speed and measuring the time and speed will allow you to calculate the hp).

So moving a fixed weight from here to there takes a certain amount of work (energy). More horsepower will mean that you can do that work faster. Torque applied to wheels under that weight will allow you to get it moving.

Now say your truck has no engine or driveline, only a rocket. That rocket will apply a certain horizontal force to accelerate you, replacing the force applied where the rubber meets the road in a truck with an engine and driveline. No torque involved, but the horsepower can still be determined, because you can measure/calculate the rate at which the rocket is doing work.

Oversimplification will just lead to some major misgivings about horsepower and torque. You can't really understand them without understanding the physics involved.

Jason

 

I know that that was what you were trying to say...I was helpin' ya get there

Understandable mistake...I understand why ya got mixed up, it's confusing. It did sound that way...horsepower is the key to acceleration but that doesn't mean torque didn't matter cuz it's in there too, no torque = no horsepower.


Pretty good Jason...nice job of explaining what you had to say.

I just try to help people visualize it through examples...then try to explain the details about how it works and what it's all about.


Most people understand what torque is, it's just the twisting force...

Horsepower is the difficult one, it's just the relationship between torque and RPM. It's measuring how much work can be done in X amount of time...torque is the amount of work and RPM is the amount of time.

The horsepower in a vehicle is what determines it's acceleration because it tells you how much work is done in what amount of time...

Two identical vehicles with the same torque but different horsepower....the one with the higher horsepower will accelerate faster because it can do the same amount of work in a shorter amount of time.

I think that is a short and sweet way to explain it without using physics.

Again....anyone have questions?? I like teaching people this stuff. My suggestion is to go out and try to make your own conclusions, it'll help you understand the concept. I came up with the examples I gave (snowmobile/saturn, monster truck, school bus)...I just simply analysed their behavior and came to the conclusion that....thats how horsepower works...tieing it all together is what makes you fully understand.

 

Your last statement in the above quote is entirely correct, but the first statements have some slight, but significant errors. The definition I gave for horsepower in my above post is straight out of a physics textbook. Your definition, "...measuring how much work can be done in X amount of time" is energy, not horsepower. Horsepower is an instantaneous quantity--it's work per unit of time, ft-lb per second. The problem is that you said RPM is the amount of time, but it's not, because RPM have the units of 1/time (revolutions is a scalar quantity--no units,). HP is basically how fast energy is being expended. To move X load Y distance will take a fixed energy, but applying 100hp will get it done 100 times faster than applying 1hp to do it. Both (assuming 100% efficiencies for a direct comparison) will expend the same energy, or do the same amount of work to do it. The 100hp worker has to have more torque also, to get that load moved faster, since it would have to have a greater propulsion force (torque applied to wheels), resulting in greater acceleration (F=ma, F is higher, m is the same, so a is higher). If the load is large enough, the 1hp worker may not even be able to overcome the frictional forces to get the load moving.

I think you're just having trouble using your terms precisely and accurately because you're trying to avoid using physics. Introduction of fuzzy definitions to try to simplify will only lead to confusion.

The reason big trucks don't have more hp is due to the torque curve, and the construction of the engine. The heavy, durable components prevent the engine from spinning at higher rpm, so at low rpm, there is little hp (dividing 1500 rpm by 5252, times 1500 ft-lbs is 428hp). If the engine were built with much lighter components, you might be able to spin it up to 5000 or 6000 rpm and have much higher hp (1500 ft-lbs times 6000rpm div by 5252rpm is 1713hp). The problem is, the lighter components wouldn't handle that for very long, since that is a LOT of energy going through them --valves slamming open and closed much harder, pistons exerting much more lateral motion in cylinder, more cycles to the crankshaft at high torque, etc. But for that short time it sure would be yanking that trailer around at high speed.

In the end, the horsepower vs. rpm curve follows/is based on the torque vs. rpm curve. If two engines have the same torque at different rpm, they're doing work at different rates (different hp, but applying the same force to/through the driveline), and their hp and torque curves will be different.

We'll get there...we're starting to zero in on the concepts...

Jason

 

Too Funny!

Let me further confuse the issue with a new interpretation:

Ok, think of a using a two-foot breaker bar on crank pulley of your truck. If you weighed 200 pounds you could apply up to 400 foot-pounds of torque. The available torque is more than your stock motor. Put the truck in neutral and you can move it easily by applying force to the breaker bar. You could even shift the gears to move it faster or slower. However beyond changing gears you could not appreciably accelerate the truck because the rate that you could perform the work (the horsepower) is severely limited.

 

Sigma - this is closer to what I was trying to say earlier with my very bad driveshaft example...