Torque.........Defined???

[rahtreelimbs]

Another thread question whether Stihl or Husky has better torque. Some will argue that the term "torque" doesn't apply to chainsaws. So what do we refer this low-end power too? There is a difference........just want to know the best terminology.

 

[sedanman]

When you wake up with "wood" and have to urinate badly. You stand in front of the bowl pushing down on your manhood, when your heels come off the ground, THAT'S TORQUE!

 

[glens]

torque is a twisting force.  In a typical engine it's the amount of twisting force present at the crankshaft journal.  All engines such as used in chainsaws produce torque, and produce varying amounts at varying engine speeds.  When you know any two values of torque, RPM, or horsepower, you can determine the third value.

Japanese motorcycles historically produced their best torque at higher RPM; Harley did so at low engine speeds.  Using that comparison, which saw, Husky or Stihl, is typically the Harley?  That's the question that's usually being asked.  But we all know that while those hogs were busy pulling stumps, the Jap bikes would run 30 rings around them...

http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm

Glen

 

[ehp]

Rich , torque does apply to saws that is why we have gears to plays with,

now torque would be a 090 compared to a 242xp ,


well at least for me , on a woodsaw i am after torque more than rpm's cause torque makes a better saw in my mind and easier to run, i like to have the saw make its max. hp. for the 80cc class in the 12000 to 12500 rpm's , now what a saw turns out of the wood does nothing ,it is what she does in the cut under load that counts


you can get the same horsepower reading from 2 different saws , one at 7000 rpm's and a screamer at 13500 rpm's just the screamer will have alot less torque

 

[scottr]

Torque

Glen, the stump pulling torque is low end torque and the ring running torque is high end torque . Paul , the heel lifting torque is ball bustin torque . What is midrange torque ?

 

[flipjack]

Power (hp) = Torque(ft-lb) * RPM / 5252. Horsepower is basically the rate at which work is done.

 

[Gypo Logger]

There's nothing quite as handy as a saw with alot of low end grunt. You know, like when you can see the chain turning around at 12"/sec. This low end grunt thing is probably just as important as the "dealer support", that gets us thru our busy cutting day.
So for that low end grunt torquey thing, I opted for an O-9-Oh with 59" bar and helpers handle, but then I got smart and said hey, why not put the 59" french frier on an 025 at full throttle?
This way, I accomplish the same thing with less weight and expense, but my dealer won't give me much support. He thinks I've spun a bearing. All I need now to complete the pkg., is a diff lock on my 025.
John

 

[glens]

Scott,

Midrange torque was my Honda V45 Interceptor.  As I recall, 3000rpm was about 50mph in top gear.  Just roll on the throttle and arms grow increasingly (linearly) longer all the way to about 11000rpm.  Or you could drop a gear (or two) and lift the front wheel, but for all-around real-world use it was the absolute ideal, and a nickel would stand on edge on the cases with the engine idling, it was that smooth.

But for cruising around town, as opposed to the mountain roads, I guess I'd like a Harley...

Glen

 

[bwalker]

When most people toque of torque what there are describing is a wide power curve. That is to say a engine that makes power down low all the way up to high rpm.

 

[Al Smith]

Torque,

a learning experiance,is running an old gear drive,and failing to properly engage the bucking spike,or dawg.That experiance,much like trying to stop a clydesdale, as the saw is dragging you over the log,you are bucking,can be defined as torque,in it's simplest form.

 

[RandD]

Torque and power diagramm

Find attached an example for the measured power output and torque for some machines. The measurement was done on a certified dyno for type approval.

You have the maximum power output when the product of torque and engine speed reaches the maximum:

Pe [kW] = Md [Nm] * rpm [1/s] * 2 * 3,14 / 1000

Example: 4,73 [Nm] * 9500 / 60 * 2 * 3,14 = 4703 W = 4,7 kW


PS: The PS-7900 RS is a limited edition (300 pcs.) with selected piston and cylinders.

 

[Crofter]

Originally posted by glens
torque is a twisting force.  In a typical engine it's the amount of twisting force present at the crankshaft journal. 

Japanese motorcycles historically produced their
best torque
at higher RPM;
Glen

Glen I am surprised to see you applying the term "best" to describe torque especially in a thread on defining torque. Torque values can be only properly defined as being "more" or "less" (or higher or lower); you are usually a stickler for being precise! lol!

Ben, I think what you are describing is generally what we prefer. We are really describing the feel of an engine. That is why there is so much confusion; feelings are very hard to accurately discribe! Actually it is the shape of the torque curve, whether it is a smooth curve or peaky, that greatly affects the feel. If it is peaky, it is hard to find and stay on it. If it is focused strongly at either low or high end of RPM range, it loses flexibility and takes more dedicated gearing to properly harness. Though it may measure higher in absolute terms of either torque or horsepower, we will likely say, subjectively, that the other more flexible engine is the more "powerful". In the right hands the one may win the race but its not what you want to operate day in day out in a relaxed fashion.

 

[flipjack]

Re: Torque and power diagramm

Originally posted by RandD
Find attached an example for the measured power output and torque for some machines. The measurement was done on a certified dyno for type approval.

You have the maximum power output when the product of torque and engine speed reaches the maximum:

Pe [kW] = Md [Nm] * rpm [1/s] * 2 * 3,14 / 1000

Example: 4,73 [Nm] * 9500 / 60 * 2 * 3,14 = 4703 W = 4,7 kW


PS: The PS-7900 RS is a limited edition (300 pcs.) with selected piston and cylinders.

Wow! Who are competitors A & B? (or will you get sued if you tell us) Also, I'm curious as to what the torque curves look like below 6500 RPM. Are they relatively flat, or do they drop off.

 

[Crofter]

Flipjack, these are chainsaws, not stump grinders; what the torque curve is below 6500rpm is pretty unimportant. The curves on the chart are very similar for all three saws, both in horsepower and torque. Operating characteristics would be very similar. My guess is that the other two saws are of a smaller displacement than the 7900. Possibly more restricted exhaust too, but just a guess. Look up the specs on 044 sthl and 372 Husky and see how close they match A and B. Think 046 and 385 would be closer on HP but heavier.

 

[RandD]

Re: Re: Torque and power diagramm

Originally posted by flipjack
Wow! Who are competitors A & B? (or will you get sued if you tell us) ...

The competitors have a little bit less displacement (77 cc & 71 cc), but nearly the same weigth 6,1 to 6,5 kg. The rated power output was not achieved (see also the measurements in this document http://www.arboristsite.com/attach/14834.pdf).

... Also, I'm curious as to what the torque curves look like below 6500 RPM. Are they relatively flat, or do they drop off.

The measurement below 6000 rpm is only a problem of the centrifugal force clutch. Ther is no drop off.

 

[WoodTick007]

Torque

Its my understanding that if two motors have the same piston size, resulting in the same compression ratio, but different crank stroke lengths. That the motor with a greater crankshaft stroke will produce more torque. I believe that this is greatly related to the inertia that is created by the greater dementions of the rotating assembly.

Maybe Rocky will have something to add. And why wouldn't he?

 

[RandD]

Re: Torque

Originally posted by WoodTick007
Its my understanding that if two motors have the same piston size, resulting in the same compression ratio, but different crank stroke lengths. That the motor with a greater crankshaft stroke will produce more torque. I believe that this is greatly related to the inertia that is created by the greater dementions of the rotating assembly.

Maybe Rocky will have something to add. And why wouldn't he?

Hi WoodTick007,

generally have the engines with more displacement a higher torque / power output.

With a higher displacement you get more charge (air and fuel) into the combustion chamber. The power (torque) is coming from the burning fuel. In a 2-stroke engine you have some leakage of unburned charge during the scavenging process. A good engine has less scavenging losses and burns most of the fuel to produce the torque at the crankshaft.

To judge the efficency of the engine, the developer of the engines are comparing the specific power output (hp per litre displacment) or the specific torque (Nm per litre displacement).

A very good value has the PS-7900 with 80,15 hp/l (= 6,3 hp / 78,6 cc).

A higher value stands for a better scavenging process and a higher efficency of the engine.

 

[Crofter]

wood tick' nothing like betting on a sure thing! If the two motors have same piston size and compression ratio but different strokes they will also have different displacements so the longer stroke one will have more torque for sure.

Usually with a given displacement, the engine with the longer stroke will have more torque. Dont bet money though without controlling all the other factors such as compression ratio and all the separate things that effect induction and exhaust.

You are joking about the heavier mass of a long stroke engine contributing to its higher torque, aren't you? Lol!

 

[glens]

Originally posted by Crofter

Originally posted by glens
Japanese motorcycles historically produced their best torque at higher RPM;

Glen I am surprised to see you applying the term "best" to describe torque especially in a thread on defining torque. Torque values can be only properly defined as being "more" or "less" (or higher or lower); you are usually a stickler for being precise! lol!

Maybe I should have said "produced their torque best at higher RPM"?

More factors than just bore/stroke ratio come into play.  If two engines of the same displacement having different bore and stroke configurations are built using the same valve sizes and timing, the one for which the valve configuration is more "correct" (better suited [subjective]) will likely be the nicer-to-use engine (for the person who prefers that type of response).

As to the torque v. RPM curves shown earlier, they are utterly meaningless as comparisons unless the full conditions and identification of the other saws and who's doing the testing for whom are all known.

Glen

 

[Crofter]

Glen, I have to agree about the room for doubt on that data as presented. It could be correct, but nothing indicates that all saws were tested under identical conditions. Temperature, accessories (such as air cleaners, mufflers), length of time tested, etc., could possibly not have been the same for the competition. I think there is sufficient similarity in the relationships to predict that characteristic operation would be similar though.