so torque's pulling power, and horsepower is how fast you will get it done. thats why trucks have torque and mustangs have hp.

ex. powerstroke has around 600 ft lbs and around 300 h.p. (i think). then theres a random truck with 600 ft. lbs. and around 600 h.p. they are towing 7000 lbs. They pull the same, (if they had the same gears), but the random truck with 600 hp is gonna tow that load faster. If the 2 trucks in my example were drag racing, the one with 600 hp is gonna win.

 

And don't forget that torque can be manipulated through your gears. My F-100 will run 90+ on the freeway, but is slow up hill and even slower carrying loads. It has rather tall gears for a truck resulting in better gas mileage and top speed and less torque at the wheels. My Jeep is the other way around. Maybe 100 HP. Torque probably under 200lb/ft but due to the ratio in the rear, I can idle around the block and up hill in 4th gear in 2wh at 25mph. Top speed is 60 and my gas mileage is horrible. But it will pull all day.

 

You're got the right idea here. But Mustangs have torque AND horsepower, it's not very biased to either one. Reason being, mustangs are sorta heavy for a car, so they need torque. Mustangs are kinda torquey cars (depending on what you compair it to). Thats just me being particular thou.

...your in the right ballpark

 

[QUOTE=MustangGT221]I've had some practice at explaining this, so hopefully I do a good job.


An electric table saw....lots of power right? Wrong, it has lots of horsepower, but very little torque. Try to turn that saw on with a piece of wood touching the blades, it doesn't have enough torque to turn the blade when it has a big load on it. When it's on, it's spinning really fast and it uses that momentum to power through cutting a piece of wood. Cutting the wood doesn't require a lot of torque, it requres speed.

[QUOTE]

I agree with everything you said except this one. Electric motors actually produce maximum torque at stall. That is one reason you need a 5hp gasoline engine to power an air compressor that only needs an (honestly rated) 1hp electric motor, because of the high starting load. Locomotives use electric traction motors instead of just gearing down the diesel engines for the same reason.

Jim

 

If you want to get real technical (some might), Hot Rod Magazine just printed a great article of Stroke vs. Bore in relation to seeing which is better for Torque and HP and if T or HP is better in general. I know they've printed other articles about it before too.

Also FYI...the new Motor Trend just printed an article about the Ford GT vs another Ferrari out in Italy, and the Ford came out of the article looking incredible. It was a great read, if for nothing else, to hear someone say how great this AMERICAN made exotic is.

 

I wasn't intending to get that technical...I was just trying to make examples...

 

since were talkin about this stuff, whats stall? i never have had any idea of what stall/torque converters do either. So if someone I know has a 5500 torque converter in his tranny, whats it do?

 

The stall speed I believe is were the tourqe converter starts to engage?? Correct me if I'm wrong but I believe thats what it is. A high stall rpm is used in drag cars so it puts converter engagment right along the lines of peak tourqe, or further up the curve anyways. Think of it as in a standard, if you just dump the clutch in a car, even slipping it fast, most cars and trucks will stall out. Raise the rpm to say 1100 rpm and do the same thing and many cars may not stall but depending on how high peak tourqe is it will bog down and you wont achieve an efficiant launch. Now raise that rpm to say peak tourqe and you may very well break the tires loose and still not get an efficient launch because all the power is being spun thru the rubber and into the pavement.

so if you install a torque converter that works nicely with the tourqe curve you can get a smooth luanch that just starts to slip the tires without boggin the engine down.

Raw torque and HP can be masked by alot of stuff, tourqe can be made up by gears, look at most tractors, I have a kabota with a 3 cylinder desiel(a whopping 60 ftlb and 18 horsepower!) and given enough traction may pull the same weight as my F-250(325ftlb) stock for stock, put lower gears in the F250 tho and the kabota wont be able to touch the 351. I ussually run out of traction tho long before I do power. torque can make a car feel faster then it is. My F250 has 325ftlbs and 210HP all at a low rpm. It sets you back in the seat as soon as you go full throttle. My nissan has 285 ftlbs of tourqe but peaks at 4000 rpm and 265 HP, it needs to build RPM before you ever feel anything, but when it does build up that power, its actually around 8 seconds or less 0-60 were as the F250 is maybe 10- 11 seconds(which considering the weight difference aint all that bad of a difference haha, 4500 pounds to 6500 pounds)

 

I dont want to come across negative here, or start anything, but you just contrudicted(sp?) yourself with these statements. HP is not going to be the only factor in acceleration-From launch, torque, gearing and weight will be the key factors on whether or not you get good acceleration. Which is exactly what you stated in the second statement that I highlighted. Until you can get high enough into the RPM range for the HP to come into play, torque will be the deciding factor.At highway speeds, a certain amount of HP is needed to say pass, or accelerate to even higher speeds.
Power is determined by how much work is done over the amount of time, so more work, and less time equals more power. Torque however, is a measured force, a twisting force. So HP can be calculated by torque as stated before.

 

I didn't contradict myself, I'll try to explain why.

I basically said when you hear horsepower, have acceleration in your mind (not in those words) because horsepower is a measure of how quickly work is done....horsepower is what gives you acceleration, torque (by itself) does not give you acceleration. Horsepower is just a mathematical calculation of torque and RPM...whenever you see horsepower, torque is there. So when I say horsepower is what accelerates you...I am also saying that torque is there as well, because torque is a part of horsepower (RPM is the other part). Get it? I said what you don't think I said.

Torque (in this context) is considered the measured twisting force at a particular RPM. The RPM has to change to see acceleration, therefore torque doesn't (by itself) give you acceleration.

I was trying to be as simplistic as possible for explanational purposes. You can pick my sentences apart but I'm just trying to explain it (generally), not write an encyclopedia...if I get too informative/descriptive...it'll just confuse people...so I leave some of the details out so people can grasp the basics of this concept.


Horsepower and torque can be very difficult to fully understand. You need experience with it to really understand it. We're only talking torque/horsepower here.....and what it actually is...some of you are starting to talk about weight/gears etc ...you're just making it confusing...stick to the basic discussion...horsepower and torque.

On a side note, this may help as well...

If you have a light car with high horsepower and low torque...like a honda S2000...it'll move a light load quickly....if you have an engine with low horsepower and high torque (big rig) it'll pull a heavy load slowly....

This can just be summed up by basic gear knowledge. If you have two gears...one gear twice as large as the other....the bigger one will spin at 1/2 the speed, but give twice as much torque (if you had a shaft connected to it). The smaller one will spin twice as fast as the larger one, but put out 1/2 the torque. Gearing is a whole different discussion...


I hope you all are getting it, I know it's hard. Speak up if you're confused.

 

"This can just be summed up by basic gear knowledge. If you have two gears...one gear twice as large as the other....the bigger one will spin at 1/2 the speed, but give twice as much torque (if you had a shaft connected to it). The smaller one will spin twice as fast as the larger one, but put out 1/2 the torque. Gearing is a whole different discussion..."

thats why when your'e hauling 2000lbs in the bed of your pick up, you start off in first gear instead of 2nd, because more torque is being put to the wheels in firsrt. in second there is less torque being put to the wheels, but you can go faster, top speed wise.

with lots of horsepower and not a lot of torque, you can move a snowmobile very fast, but not pull any weight. with a lot a torque and not a lot of horsepower, that snowmobile wont go very fast, but and tow more...if you tow with a snow mobile.

 

You've got it backwards. All the horsepower in the world will not accelerate anything. Acceleration = force/mass. Horsepower is not in that formula anywhere. If you apply a 500 lb net force to an object it will accelerate the same whether it is going 100 mph or standing still. The key word here is net. I'll use my truck as an example since I now what its power curve looks like. It makes about 170 hp @ 3200 rpm and 320 ft-lbs at 2000 rpm. 2000 rpm is conveniently the rpm when I'm going 60 mph. The truck is a 5 speed with 3.08 gears and tires that are 12.75" from centerline to pavement. For arguments sake, let's say it takes 400 lbs of force to push the truck down the road at 60 mph (88 ft/sec). 400 x 88=35200 ft-lbs/sec. There are 550 ft-lbs/sec in a horsepower, so it takes 64 hp to push the truck down the road at 60 mph. At 2000 rpm, 64 hp = 168 ft-lbs. If we check our math by multiplying that through the gears we get 168x.8x3.08/1.0625 = 389.6 lbs. 168 is the torque required, .8 = 5th gear, 3.08 = axle gear, and 1.0625= tire height/24. We're within 3-4%, so the numbers should be good. We know it takes 64 hp to go 60 mph, and we know that it takes 168 ft-lbs of torque to do that. If you put the pedal to the floor and the torque goes to 320 ft-lbs you accelerate using the 152 ft-lbs that aren't being used to go down the road. The force at the wheels goes to 320 x .8 x 3.08/1.0625 = 742 lbs. If the truck weighs 4000 lbs the initial acceleration will be about 6 ft/sec/sec, or 4 mph/sec. As the force required to maintain speed increases, the rate of acceleration decreases because there is less net force available to do work on the truck. The hp available at 2000 rpm is 122, so at 60 mph the truck is capable of maintaining speed as long as the force required to do so does not exceed about (drum roll please) 742 lbs.

 

yeah SS you lost me on that one...

 

Yes, it's basic gear reduction princples.

Be careful with wording here. With lots of horsepower and low torque, you can acclerate a light vehicle (the snowmobile) quickly. If you made that snowmobile much heavier, there wouldn't be enough torque to help make it accelerate quickly. It's not that it "won't pull any weight"....it's that if you added more weight, it's ability to accelerate quickly would decline*.


When I gave my examples of snowmobile vs saturn, I wasn't thinking of the snowmobile towing something, I was just comparing the 700 lb snowmobile vs a 2500-3000lb car because they both have an engine with the same horsepower rating, but very different torque and weight.

Let me re-phrase your statement a little bit. "with a lot of torque and not a lot of horsepower, that snowmobile won't accelerate as quickly." Let me give you another example to illustrate the second 1/2 of your statement ("tow more").

Take a big diesel school bus. Low hp, high torque. Does it's acceleration change that much when it's loaded with kids? No, it doesn't. When it's loaded up with kids or when it's not loaded up, its acceleration will be slower when heavier but the change is not drastic. Thats because it has low horsepower and high torque. Since it has low horsepower, the amount of weight on it doesn't affect acceleration all that much. It'll acclerate slowly anyway because the horsepower is so low. If it was a high horsepower/high torque school bus (cool!) it would accelerate quickly loaded or unloaded (monster truck example). Notice how both the school bus and monster truck are heavy vehicles, and they both have lots of torque. The school bus accelerates slowly because it doesn't have much horsepower, the monster truck accelerates very quickly because it has a lot of horsepower.

*say instead that the diesel engine in that bus had high horsepower and low torque. When it got loaded up with kids, the lack of torque would be very obvious, and lower the vehicle's acceleration considerably. This coincides with my snowmobile/saturn example. 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.



I don't have it backwards...you don't understand the point I'm trying to make here.

You're bringing physics into the mix here...and your example is just confusing me as well as others.

All we're trying to do in this thread, is define horsepower and torque. All I've been doing here is trying to explain what horsepower and torque is. I've stated what they are...and given examples of how it works. Leave physics out of it for now please. They're just trying to grasp the basics.

If you want to be 100% correct, horsepower is VERY RELATED to acceleration. Again, I am trying to teach you guys what horsepower and torque is. It's a very difficult concept to explain over the internet. When you're trying to teach somebody something, you've got to be careful how you word things so you don't confuse them, lets not be so politically correct.

 

And you've said repeatedly that horsepower accelerates a vehicle and that is 100% wrong. Torque is the one and only thing that causes a vehicle to accelerate. You could build an engine with 1000 hp and it won't go anywhere unless there is some torque behind it. Conversely, if you build an engine with 1000 ft-lbs of torque it will do about anything you want it to. Horsepower is a facade!