The torque's non existing influence on cutting speed.

[peter399]

I just have to make a comment on this "torque issue" that I see in many many threads. Torque is a thing invented by car magazines that has totally overtaken peoples minds: Statements like: My car (or chainsaw like we discuss here ) performs so great because it has tons of torque... is totally BS IMO.

What we want for a car to accelerate or a saw to cut fast is high torque on the WHEELS/DRIVE SPROCKET, not in the engine! The only thing that determines the speed of the car / saw / whatever machine you want, is POWER. Now, for those of you that have done some physics it's easily described the following way:

Power = Torque * angular velocity (1)

we also have:

Torque 1 * angular velocity 1 = torque 2 * angular velocity 2 (2)

now, let's say that

Torque 1 = engine torque
Torque 2 = drive sprocket torque
angular velocity 1 = engine rpm
angular velocity 2 = sprocket rpm

Combining (1) and (2) we get:

drive sprocket torque = (engine torque * engine rpm / sprocket rpm) = engine POWER / sprocket rpm !

So what you want is high power and a low transmission. There is a reason why they build F1 cars with high power at high rpms with low transmission..

A Formula 1 engine with 601 HP and 400Nm of torque will hence pull a fully loaded truck up the hill quicker than would the truck engine with 600HP with 2500Nm torque. The reason trucks use 16liters diesel engines is because they will last a bit longer than the F1 engine..

Same goes for chainsaws: A 5,4hp chainsaw will always cut faster than a 5,3hp chainsaw . If the 5,3hp chainsaw has higher torque in it's technincal spec. the only thing that this figure says is: This saw has it's max power at a lower rpm than the 5,4hp saw. But the higher rpm of the 5,4hp saw gives a smaller drive sprocket for the same chain speed (= lower transmission) and consequently the 5,3hp saw will be outcut, regardless of it's torque.

I hope it wasn't too fuzzy, just wanted to clear this out. Drop torque and go for high power!

- Peter

 

[Freakingstang]

This is gonna get ugly, mark my words. I don't agree with you , but will wait 24hours before responding.....

Remember HP is a function of torque and RPM......

 

[Canyon Angler]

What's a "low transmission"? :monkey: opcorn:

 

[Sprig]

opcorn: opcorn: opcorn:
Gawd I love dirty talk!opcorn:
opcorn: opcorn: opcorn:









nm, gtg ta bed *yawn*

 

[blis]

Man, i wish everything was so simple, but we dont live in perfect world....

 

[SmokinDodge]

Power = Torque

- Peter

I'd say you summed it up nicely Pete.

 

[peter399]

Yes, maybe We'll see. Especially since there are so many Americans here that like GMC , Chevys and so on. Not to mention Harleys! Can't wait to have the discussion But seriously, this is an important issue since many of the discussions in this forum can be related to this in some way.

/Peter

 

[Canyon Angler]

So...let's see.

By your logic, if I have an 9 horsepower chainsaw geared/sprocketed such that it has a chain speed of only 50 feet per second, it's still going to out-cut a 3 horsepower chainsaw with a chain speed of 500 feet per second, simply because it has more horsepower?

I don't think so, bud.

 

[peter399]

What's a "low transmission"? :monkey: opcorn:

Sorry, as english is not my mother tongue I don't know the correct expression for it. What I want to say is for example:

if you have 200 Nm on the crank shaft in your car and your transmission is 10:1, you will have 2000 Nm on the outgoing shaft from the gear box.

That describes how insignificant the torque (of the engine!) is when it's connected to a gearbox. Power however, is how much work can the engine do (per time unit) and that is important!

/Peter

 

[peter399]

So...let's see.

By your logic, if I have an 9 horsepower chainsaw geared/sprocketed such that it has a chain speed of only 50 feet per second, it's still going to out-cut a 3 horsepower chainsaw with a chain speed of 500 feet per second, simply because it has more horsepower?

I don't think so, bud.

No, that's not what I wrote. If they have the SAME chain speed, the saw with the higest power will always win. Read the example again. Again sorry for not being clear enough.

/Peter

 

[blis]

if there are 2 engines, with lets say 5nm and 10nm torque, the first one has to rev twice as much than the other one to produce same power...

just a thought...

 

[Freakingstang]

What's a "low transmission"? :monkey: opcorn:

A torque multiplying apperatus.... LOL

 

[Freakingstang]

ok, try this.

two motors, same end horsepower. same basic engine size. Same chain speed

One has a long rod (stroke) and the other is shorter.

Which one is faster and why?

Which one will have more torque?

 

[Canyon Angler]

I like the new Shimano saltwater reels that claim to have BOTH more torque (for more winching power) AND a higher gear ratio (for more inches of line retrieved per revolution of the heel handle) all in ONE!

That's a pretty good trick!

 

[peter399]

ok, try this.

two motors, same end horsepower. same basic engine size. Same chain speed

One has a long rod (stroke) and the other is shorter.

Which one is faster and why?

Which one will have more torque?

Once they have both reached their peak power they will be equally fast.
I would hovever choose the faster reving "big bore and short stroker" than the more "steam machine" like "long stroker". Since they have the same power, the one with the lower rpm will have the most torque. But there are other factors than bore/stroke that determines max rpm I guess? (I'm not an expert on that I must say.)

/Peter


/Peter

 

[blis]

Once they have both reached their peak power they will be equally fast.
I would hovever choose the faster reving "big bore and short stroker" than the more "steam machine" like "long stroker". Since they have the same power, the one with the lower rpm will have the most torque. But there are other factors than bore/stroke that determines max rpm I guess? (I'm not an expert on that I must say.)

/Peter


/Peter

The max speed is determined by porting, exhaust, stroke lenght, piston diameter and piston speed...

 

[Ianab]

The HP rating determines how fast a saw can theoretically cut, assuming you can keep the saw at those revs.

Back in the real world, a saw with a better torque curve may cut faster because as the revs drop off the saw still has the torque to keep cutting. An engine designed for max power only drops off very quick once the revs drop below it's optimum rpm.

A saw with good torque is just easier to use, and out in the real world usually cuts better than a peak horsepower engine that has to be run 'just right'. A high torque saw you notice the revs are dropping a bit, and ease up on the cut and keep going, a saw with poor torque curve just bogs as soon as the revs drop.

The difference between theory and practice

Cheers

Ian

 

[peter399]

The HP rating determines how fast a saw can theoretically cut, assuming you can keep the saw at those revs.

Back in the real world, a saw with a better torque curve may cut faster because as the revs drop off the saw still has the torque to keep cutting. An engine designed for max power only drops off very quick once the revs drop below it's optimum rpm.

A saw with good torque is just easier to use, and out in the real world usually cuts better than a peak horsepower engine that has to be run 'just right'. A high torque saw you notice the revs are dropping a bit, and ease up on the cut and keep going, a saw with poor torque curve just bogs as soon as the revs drop.

The difference between theory and practice

Cheers

Ian

I agree with you Ian. Very good point. Like with cars, the high torque car is easier to drive because you don't have to be an expert on changing gears. But if you have modern automatic , the electronics will handle that for you .

Anyway, my point is that the torque itself doesn't have anything to do with performace or max cutting capacity. When you refer to a saw having higher torque at lower rpm's, it actually has the same power at lower rpm's, or a more flat power curve and hence a wider useable power band, making it user friendly in everyday cutting. Like comparing a 346 to a 353. The 346 is less forgiving than the 353 for mistakes ( not running at peak power rpm). But if you can handle it, the 346 will be faster since it has more horsepower.

I like to refer to Harleys 1100 cc and lot's of torque but slower than a 250cc Japanese motorcycle with more horsepowers.

 

[BostonBull]

I like to refer to Harleys 1100 cc and lot's of torque but slower than a 250cc Japanese motorcycle with more horsepowers.

Now you are comparing apples and oranges....stick with chainsaws!

Harley doesnt make an 1100 cc right now 1000 and 1200 is the closest. And the Harley is an air cooled, 45 degree engine, made for.........wait for it.......................TORQUE!!!!!!

250cc Japanese engines are USUALLY 90 degree, liquid cooled, made for PEAK HP.

Harley will usually grab most of these bikes off the line for a VERY short distance because of their TQ.

Dont forget TQ gets you off the line HP carries you the rest of the way. If TQ isnt as important in saws than why do most of the saw builders build it into their engines? So that we can push down harder, which in turn makes the saw cut faster, and we dont have to worry about losing the max power as soon and thus bogging the saw down or even stalling it in the cut.

*I am no expert I just believe this guy doesnt have the whole story.....and you opened a huge can of worms!!* opcorn: opcorn: opcorn:

 

[Crofter]

If you have to use gearing to make an engines output suitable for the work, it is often too expensive, complicated or energy consuming to include gear reduction. In a chainsaw you really practically only have a choice of 7 or 8 tooth sprocket on a standard setup.. With blowers or pumps there is loss of efficiency if you attempt to simply turn a smaller impeller faster. Bearing survival and other mechanical issues become limiting factors if you start to pursue high rpm and low torque to produce your horsepower. Really high rpm output of a chainsaw gets more and more dependant on resonant charging and the powerband becomes increasingly narrow; it just takes tons more attention to work with a narrow power band machine whether it is a bike, a saw or whaterver!