Torque ratings - I'm bored

[harrygrey382]

Hmm, revision for finals... I reckon now's the time to compile a torque ratings chart - we all know the hp ratings of all the saws (well, I'm sure sawtroll does anyway). But I want to compare torques (I like torque...), purely for interest's sake. I've got them for 041,051 and 075, but is there anywhere I can look them up. Stihl only gives HP online, what about husky/Jred? Is there anywhere else I can look?

How about people post the torques from their service manuals and I can compile them all - is there anyone else out there as bored (work dodging) as me?

saw hp/rev lb-ft(Nm)/rev

041av 3.7/7500 5.2(3.8)/5000
051av 5.8/7000 8.0(5.9)/5000
075/076 7/7000 9.2(6.8)/5000

 

[belgian]

Where's Troll when you need him :hmm3grin2orange: :hmm3grin2orange:

 

[volks-man]

just a thought

in automobiles there is a formula to figure horsepower from a timed run divided by the weight of the car or something, ect.........
i believe there is a way to calculate torque from horsepower specs as well. it may not be very precise on a small engine because the margin for error may be close to what torque the engine makes.

 

[kevin j]

Understanding the concept is easy, the units get ugly.

Work done is force or torque applied through a distance
Power is work done per unit of time
Rpm is the distance turned in a unit of time,

so torque times rpm is power, with a bunch of unit conversions.


HP is (torque ft-lbs) x (rpm) / 5252

or (T inch-lbs x rpm) / ( 5252 x 12) = (t in-lbs x rpm ) / 63024

so algebra, rearranging to T = (HP x 63024 ) / rpm


I don't have the unit conversons here for newtons meters etc.

kcj

 

[harrygrey382]

Understanding the concept is easy, the units get ugly.

Work done is force or torque applied through a distance
Power is work done per unit of time
Rpm is the distance turned in a unit of time,

so torque times rpm is power, with a bunch of unit conversions.


HP is (torque ft-lbs) x (rpm) / 5252

or (T inch-lbs x rpm) / ( 5252 x 12) = (t in-lbs x rpm ) / 63024

so algebra, rearranging to T = (HP x 63024 ) / rpm


I don't have the unit conversons here for newtons meters etc.

kcj

Good eqns there kcj, (looking at similar(ish...) for my advanced dynamics at the mo!). But you still need to know the RPMs for peak torque - quicker to look them up if they exist. Or can you work it out purely from max hp/rpms, peak torque that is?

 

[SawTroll]

Where's Troll when you need him :hmm3grin2orange: :hmm3grin2orange:

In bed.....

 

[chrispy6822]

Understanding the concept is easy, the units get ugly.

Work done is force or torque applied through a distance
Power is work done per unit of time
Rpm is the distance turned in a unit of time,

so torque times rpm is power, with a bunch of unit conversions.


HP is (torque ft-lbs) x (rpm) / 5252

or (T inch-lbs x rpm) / ( 5252 x 12) = (t in-lbs x rpm ) / 63024

so algebra, rearranging to T = (HP x 63024 ) / rpm


I don't have the unit conversons here for newtons meters etc.

kcj

And for those who cannot see it from Kevin's excellent formulas torque and HP are always the same at 5252 RPM. That is a motor that makes 10hp at 5252rpm, also makes 10 ft-lbs.

 

[SawTroll]

Understanding the concept is easy, the units get ugly.

.....

Sure does, and max torque appears at much less rpms than max power - so you can't calculate the max torque from the max power.......


DLG and KWF dyno test their test objects, and list both numbers in the test reports. Those reports are the only place where I have seen torque numbers listed for Husky saws.

Stihl often list max torque in the workshop manuals.

 

[harrygrey382]

Yes but what I'm trying to say is, you can't work out peak torque from just the max hp@rpm, you need to be quoted peak torque... or have access to further graphs

edit - Troll beat me to it

 

[harrygrey382]

DLG and KWF dyno test their test objects, and list both numbers in the test reports. Those reports are the only place where I have seen torque numbers listed for Husky saws.

are these available online?

Stihl often list max torque in the workshop manuals.

yeah - I guess it's a long shot as someone has to be prepared to waste as much time as me and have the relevant manuals in front of them...

 

[chrispy6822]

Good eqns there kcj, (looking at similar(ish...) for my advanced dynamics at the mo!). But you still need to know the RPMs for peak torque - quicker to look them up if they exist. Or can you work it out purely from max hp/rpms, peak torque that is?

This might help. Torque is measured not HP (most likely on a dynamometer). HP is derived from a formula, as Kevin posted HP= T x rpm / 5252.

Given the nature of the formula max HP and Max torque the max and min are not relative in a linear fashion except of course at 5252 RPM.

In the case of chainsaws with their very narrow powerband (read high HP across a narrow range of RPMS), one could argue that the ft-lbs of torque is most likely within 5% of the HP rating.

 

[SawTroll]

....
In the case of chainsaws with their very narrow powerband (read high HP across a narrow range of RPMS), one could argue that the ft-lbs of torque is most likely within 5% of the HP rating.

Not at all, because the max power usually is at much higher rpms than 5252....

Btw, I have never seen a good defination of powerband.

 

[SawTroll]

are these available online? ...

There are links in the "Reference links" tread.

 

[harrygrey382]

This might help. Torque is measured not HP (most likely on a dynamometer). HP is derived from a formula, as Kevin posted HP= T x rpm / 5252.

Given the nature of the formula max HP and Max torque the max and min are not relative in a linear fashion except of course at 5252 RPM.

In the case of chainsaws with their very narrow powerband (read high HP across a narrow range of RPMS), one could argue that the ft-lbs of torque is most likely within 5% of the HP rating.

But it's not - look at the ratings I posted at the top - 5000 is within 30% of the max hp rpm (7000)...

They are different, and I think torque should be quoted along side HP, just like when you look at car specs.

Not at all, because the max power usually is at much higher rpms than 5252....

Btw, I have never seen a good defination of powerband.

Isn't it pretty loose - as in RPM range of useful hp or torque?

There are links in the "Reference links" tread.

heading there now...

 

[chrispy6822]

Not at all, because the max power usually is at much higher rpms than 5252....

Btw, I have never seen a good defination of powerband.

I agree. Maybe I did not say it right Torque and HP are the same at 5252 rpm but that does not equate to the max HP or torque.

I think you are correct on a definition of powerband and it surely is a subjective measure. I always defined it as a very narrow RPM range where most of the useful power is available.

 

[SawTroll]

.... Isn't it pretty loose - as in RPM range of useful hp or torque? ...

That is a pretty common one, but wrong imo - as many saws have useful power way above the max hp rpms, while others fall off pretty fast above that rpm number.

To judge what performance to expect, we really need the complete curves, not only the peak numbers - and then a lot of other factors enter the picture as well - so it really is a lost case..........

 

[chrispy6822]

But it's not - look at the ratings I posted at the top - 5000 is within 30% of the max hp rpm (7000)...

Not following you there.

They are different, and I think torque should be quoted along side HP, just like when you look at car specs.

I am pretty sure it is pure marketing rating only in HP. Even like you mentioned with cars we only see the peak HP and Toque advertised. What really should be advertised or available from the manufactures is the chart.

That is why you have kids today thinking a 4 banger with a max rating of 200hp will outrun a V8 with a max of 200hp.

 

[chrispy6822]

That is a pretty common one, but wrong imo - as many saws have useful power way above the max hp rpms, while others fall off pretty fast above that rpm number.

Then that would assume that the max torque is close to the max HP or at least the torque is very flat along the RPM range.

To judge what performance to expect, we really need the complete curves, not only the peak numbers - and then a lot of other factors enter the picture as well.

Agreed. But I was about to question what other factors? Then it dawned on me clutch performance. Almost like we need a BHP for saws as well as the complete power curve to see the true performance of a saw rather then crank HP.

Having that info could or could not really turn the world of chainsaws around.

 

[SawTroll]

.....
That is why you have kids today thinking a 4 banger with a max rating of 200hp will outrun a V8 with a max of 200hp.

It may very well do just that, if the 4 cylinder one is a Turbo.....

 

[harrygrey382]

Not following you there.

I was just saying the peak torque was 30% of the rpm of peak HP not 5%! In the case of an 051

I am pretty sure it is pure marketing rating only in HP. Even like you mentioned with cars we only see the peak HP and Toque advertised. What really should be advertised or available from the manufactures is the chart.

That is why you have kids today thinking a 4 banger with a max rating of 200hp will outrun a V8 with a max of 200hp.

I can believe that - and as for the outrunning of a 4cyl, I guess it depends on how quick revving and light the car was, but I'd put money on the V8...

It may very well do just that, if the 4 cylinder one is a Turbo.....

Just so long as it was light and unlayden. Personally I think revvy screaming power is a w4nk