torque.....what the...?

69.5Mav":krr3vi6t said:
.... you could never build an engine with, for the sake of argument, 1000 f/lbs of torque and only say 50 HP. But if you could its Acceleration would be very high because Torque is directly proportional to Acc....

Oh really? In 1921 the Rumley OilPull model 30-60 tractor was tested at the Nebraska Tractor test station. It developed 75.6 hp @ 375 rpm for a torque rating of 1058 lbs/ft. This from a two-cylinder engine displacing 1,884 cubic inches. I daresay its accelleration wasn't gonna put the scare into Don Garlits, however.

A 50 hp engine @ 1000 lbs/ft torque would be operating at about 262 rpm. This would require a lot of displacement and a really long stroke.

Acceleration means some work is being accomplished in a given time frame. This is properly measured in Horsepower. Torque does zero work.
Joe
 
With a flat torque and hp from 100 to 10,000 rpm?

I guess I should have stated that in the first place. I never thought anyone would get so caught up in the details.

I have simplified these engines to the extreme in order to illustrate the effects of Torque and HP. They are not real engines and could never be built.

No torque does work. Torque at any given rpm is also associated with a HP rating which is the maximum work that can be done at that RPM.

Torque at the rear wheels divided by the radius of those rear wheels is equal to force twisting them which in turn is the force accelerating the Vehicle if there is no wheel slippage. Force times distance moved equals work. See http://hyperphysics.phy-astr.gsu.edu/hbase/work2.html .

Now for your tractor example. I am a city boy so what I know of farm stuff is extremely limited but here goes. Because torque equals force * radius the tall tires of the tractor would significantly reduce the force available to Acc. the tractor. Also the engine is specific built for a tractor and as such will have lots of engineering compromises that will limit its use for any other purpose. A red line of 262 rpm would be one of those limits. At the same time using Don Garlits’s drag engine in a tractor would be silly for oh so many reasons not the least of which is that it probably wouldn’t work to well. At only 76.5 HP the tractor engine would have a top speed of only about 110 mph so even if it could acc up to that speed faster then Don Garlits he would still blow by it at 200+ mph.
Now if you had 1000 HP and a reasonable rpm curve you'd probably have a good drag car.

I was not aware that any body actually built an engine with 1000 ft/lbs torque at 50 HP so let me change the specs of the engine, since its imaginary It can take any value, to 10,000 ft/lbs torque and 50 HP flat from 100 rpm to 10,000 rpm. It’s a thought experiment and does not have to be an engine that anyone could build.
 
Isn't acceleration the slope of the rise in speed? Force is pressure and work is force moving through a distance. IIRC from high school physics, great force can be exerted on an immovable object without work being done. On the other hand, a small object can be moved through space with little force but work is being done.
If a force is allowed to act through a distance, it is doing mechanical work. Similarly, if torque is allowed to act through a rotational distance, it is doing work. Power is the work per unit time.
So torque is angular force.
Mathematically, the equation may be rearranged to compute torque for a given power output. However in practice there is no direct way to measure power whereas torque and angular speed can be measured directly.
That is because torque is measured as a function of the distance from the axle whereas power applies to every point of the object in motion.
However, time and rotational distance are related by the angular speed where each revolution results in the circumference of the circle being travelled by the force that is generating the torque.

I wonder if Issac Newton's enemies will go in there and change some of that stuff around just to get to us.
 
I would suspect the primary reasons for tractors and the like having relatively low rpm engines are for longer life cycle, fuel economy, cooler engine, higher compression, etc. And if you have ever been behind a tractor for 10 hours at a time, you don't want to be manipulating an accelerator pedal for every slight incline or depression, let alone having an engine screaming at you .... the concentration is on what the terrain ahead is and if the equipment you're dragging behind is working.

To get the tractor to change from say 600 rpm to 1000 rpm takes a fair amount of time, probably longer than it takes an oversquare engine to go from 3000 rpm to 6000 rpm. Just the reciprocating mass and inertia tends to slow things down on a grunter. So to say engine torque is an indicator of vehicle acceleration is not necessarily correct, it's the wheel torque that is an indicator of car acceleration. While you're still winding out your 5500 rpm redline big V8 in first, that little turbocharged equal powered car next to you has already snapped into third with an average torque at the wheels greater than yours over the time and he's beating you.
 
ludwig":2wytmrqw said:
....
If a force is allowed to act through a distance, it is doing mechanical work. Similarly, if torque is allowed to act through a rotational distance, it is doing work. Power is the work per unit time.

So torque is angular force..

Yup. As explained above, torque is a twisting force. No more, no less. When torque is applied with no movement, no work is done.

In electricity, Voltage is the force. You can have voltage present at the wall outlet, but until current flows (something moves) no work is done.

Gravity is also a force. And since it is holding me down in this chair, no work is being done. And if I don't go pack some forewood in for the night, Mama is likely to do some work by taking a broom to me.

It is easy to confuse "Force" with "Work". No matter how much force is applied, if no nothing moves, then no work is done. And no matter how little force is applied, if something moves, then work is done.
Joe
 
Just so.

As a ham radio manual explained it, carrying a rock up to the top of a stepladder is adding potential energy to the rock. When you set the rock on the step and climb down, the energy in the rock is stored and it remains stored as long as the rock sits there. When the rock falls, the potential energy is realeased.
 
RMT

It looks like your post is misquoting me as I did not say that.

XPC66

Of course you have to factor in the trans and diff. gear ratios but those are know quantities and a set ratio for any trans gear and diff gear if it has more than one speed. Also the tire radius is usually fairly constant unless you have a drag slick. So Acc = (( torque/ tire radius)*gear ratios)/ ( vehicle mass). So ACC is directly proportional to torque, in other words Acc = torque * Constants.

Lazy JW

Just so. If there is no movement then no work is done. I suspect we're tripping over semantics here as I agree that work is properly measured in HP * time. One of the tests I use to see if a formula is correct is to examine it for unit equality. I mean the if one side of an equation is looking for ft/sec the other sides units should resolve out to ft/sec. So (( torque/ tire radius)*gear ratios)/ ( vehicle mass) should be equal to HP * Time. Unfortunately I don't have my Physics Reference at work other wise I could check.
 
Mav:

Yes it looks that way, but I was quoting Joe. Sorry, didn't have my clicks down properly.

It just seems odd to me that if someone asks "what muffler sounds best?" there will be responses ad nauseum. But if a thread is about the stuff we should all know first before we do anything else, and someone makes a statement (like Joe did) that should (seems to me) lead someone to ask for more information, no one does. I figured the link might give a quick tutelage on the subject.

Ludwig, some study found that in Wikipedia most of the objective stuff is really quite accurate due to the open form it has. If something is wrong, a date, a formula, whatever, someone else will fix it. Where Wikipedia might fall flat is the subjective stuff. The date of a battle between the French and the English will be accurate, why the battle was fought?, well...
 
Just click over to Discussion section on Wikipedia. There will be egg heads haggling over the law of gravity and whatever else. Heck, they didn't even formalize the order of operations [MDAS] in Algebra until the late 1800's so that could be a hot topic too. There are guys currently trying to disprove relativity. So it's no joke. On the other hand, those Newtonian calcs have worked out pretty well for NASA, so I'll go with them on that (and with you too).
 
rmt":oty9jk3i said:
....

It just seems odd to me that if someone asks "what muffler sounds best?" there will be responses ad nauseum. But if a thread is about the stuff we should all know first before we do anything else, and someone makes a statement (like Joe did) that should (seems to me) lead someone to ask for more information, no one does....

Amazing, isn't it? I made that statement hoping to stir things up a bit and stimulate some thought :D Seems like most of the youngsters only are interested in shiny wheels and loud pipes though :roll:
Joe
 
I have a thought, that being that since "Acceleration is the time rate of change of velocity and/or direction", and a rotating mass is constantly changing direction then torque might be considered a product of rotational acceleration.
 
rmt":3k61l7ii said:
Lazy JW":3k61l7ii said:
69.5Mav":3k61l7ii said:
Acceleration means some work is being accomplished in a given time frame. This is properly measured in Horsepower. Torque does zero work.
Joe

I guess no one else will say it, so I will.

WHAT!?


I'll give him an amen. Its like the mathemtician verses the engineer. The mathematicain says it can't be done. The engineer says, yes, but I'll get blQQdy close!


Granted, before power was, there must be torque, as power is a dependant variable. Torque is the independent product of the PLAN formula. By dimensional analysis, torque is fundamental, and to dispecne with it is absurd. Nonetheless, hear me out:-


'Maximum indicated Torque ratings' are totally irrelevent to the performance of the car, if the car is geared to suit. Honda, Mazda, Ferrari, Lamborghini proved that years ago. For a 1979 Mazda RX-7 125 HP does 125 hp of work. For a 375 HP car, 375 hp does 375 hp of work. It doesn't matter if the 125 hp car has a 12a rotory engine or 125 hp 250 i6.

Indeed, even an early 375 hp at 8000 rpm 4 litre LP 400 Countach S V12 verses say, a 429 big block yielding 375 hp in a Pantera, 375 hp does 375 hp of work. The Countach has about 268lb-ft of torque at 5000 rpm, the big block could have about 500lb-ft at 3500 rpm.

Power is Torque, with a speed factor. When all is said and done, the 125 hp at 5250 rpm engine with 125 lb-ft torque at 2500 rpm will not beat or loose against the 125 hp at 3500 rpm engine that has, say, 215 lb-ft at 1800 rpm, so long as all else is equal with regard to the car its in, ites weight, its areodynamics, and as long as its gearing is optimised to the power curve.


So a 1979 Mazda RX-7 weighing 2400 pounds will not beat a 250 I6 engine if its in the same 2400 pound car.

The only time torque is of value is when you can't gear a car to suit. A perfect example was a 1982 Mazda RX-7 verses a 5735 cc Chev Z28 at Bathurst, Mount Panarama in 1982. Both cars had the same power to weight ratio, similar drag factor, and yet the Five speed Mazda lost seconds every lap becasue the 4 speed Zee 28 never had to make a third the gear changes the RX-7 driver did. At every other race of the Australian Touring car champoionship, the Mazda romped ahead, but when a 3.85 mile track with 625 feet to climb each lap is used, and the car doesn't have seven gears to cover for the relative lack of torque, it'll loose everytime. A journalist drove the 350 hp at 8000 rpm Rx-7 racer, and asked the owner, Alan Moffat, how much torque it had. He said, "you've driven the thing, it doesn't have any". As a mathematician, he was dead wrong, but as a race car engineer, he was dead right.
 
JackFish":gm75rom8 said:
I have a thought, that being that since "Acceleration is the time rate of change of velocity and/or direction", and a rotating mass is constantly changing direction then torque might be considered a product of rotational acceleration.

Think in polar co-ordinates. The equations all change units. Instead of F = M x A you get T = J x α where T is torque, J is the polar moment of inertia and α is angular acceleration. Similarly work changes from W= F x S (work= force x distance) to W = T x ω (work = torque x angle of rotation)
 
xecute

rmt said:
Lazy JW wrote:
69.5Mav wrote:

Acceleration means some work is being accomplished in a given time frame. This is properly measured in Horsepower. Torque does zero work.
Joe


I guess no one else will say it, so I will.

WHAT!?


The above is a misquote since I never wrote the above quoted line RMT started it. Please dod not continue it.

About the body of your post I agree. HP the the amount of work an engine can do. That work will be done over coming the various frictional losses involved in propelling a vehical forward, mostly air resistance. If you have the gearing to match the load to the engine then any engine with the same HP rating will reach the same top speed with in reason. I mean a nuclear pile rated at 125 HP, if such a thing exsisted, would either weight to must with proper shielding or go through drivers on a regular bassis.
 
69.5Mav":10poybzm said:
The above is a misquote since I never wrote the above quoted line RMT started it. Please dod not continue it.

Come on, Mav. I apologized for my sloppy clickwork, that is, quoting Joe while in the midst of your post. It really is NO BIG DEAL. I left his name in it, everyone knows I was quoting Joe not you. I simply quoted him from your post, that's all.

69.5Mav":10poybzm said:
I never thought anyone would get so caught up in the details.

Me neither. :wink:

Roger
 
RMT

I know and I'm not triing to harp on you but when I see it repeated I fill I have to correct it but Am at a loss as to how to explain with out mentioning you. It is not a complaint but an explanation so anyone who repeats it will know where it started. I really hope this is the last we will see of it. I hope that some people gainedsome new insight into their engines from this lively debate, I know I did.
 
Back
Top