Torque vs HP - again!

[mender]

The fact that BSFC uses horsepower and not torque should tell something about which one is more important. 

 

Mercedes is claiming their F1 engine has exceeded 50% thermal efficiency, a number only previously achieved by large marine diesels. 

Edited December 24, 2021 by mender

[Grant]

Power is what accelerates cars. Torque is just force around a circle. Like force it's an entirely meaningless number in this context unless paired with speed, in which case it becomes power.

[mender]

Close: force accelerates cars (mass), power brings time into the equation.

[Grant]

Force already has a time component. It's mass * distance / time^2. Power is force * speed, i.e. mass * distance^2 / time^3.

 

Force / time is momentum.

Edited December 25, 2021 by Grant

[mender]

That assumes there's a distance involved. 

[Bandit]

Torque is measured. Horsepower is calculated.

[wvumtnbkr]

Wait, does force actually have a distance involved, I don't think it does.  Power does.

 

I can exert 225 lbs of force on the ground with no distance measurement.

 

Work is force x distance.  Power is work / time.

 

Therfore power = (force x distance) / time.

Edited December 25, 2021 by wvumtnbkr

[wvumtnbkr]

16 hours ago, Bandit said:

Torque is measured. Horsepower is calculated.

Not exactly.  Force at the end of a moment arm is measured.  Torque is calculated knowing the moment arm length.

 

So, dynos actually measure force.  Then calculate torque.  Then calculate power.

[mender]

4 hours ago, wvumtnbkr said:

Wait, does force actually have a distance involved, I don't think it does.  Power does.

 

I can exert 225 lbs of force on the ground with no distance measurement.

 

Work is force x distance.  Power is work / time.

 

Therfore power = (force x distance) / time.

The other way to determine force is to see how quickly a known mass is accelerated. That one requires distance.

[hotchkis23]

This is why I love these forums, getting to see all the knowledge that members have is awesome!

[mender]

On 12/24/2021 at 8:25 PM, Grant said:

Force already has a time component. It's mass * distance / time^2. Power is force * speed, i.e. mass * distance^2 / time^3.

 

Force / time is momentum.

From what I've read, Force = Momentum/Time

 

To isolate Momentum, both sides get multiplied by time so Force*Time = Momentum.

 

As always, putting in the units helps to see how it all works. In metric (I'm Canadian!), a 15 newton force applied for 3 seconds = 45 kg m/s (momentum).

 

Edited December 26, 2021 by mender

[enginerd]

2 hours ago, mender said:

As always, putting in the units helps to see how it all works. In metric (I'm Canadian!), a 15 newton force applied for 3 seconds = 45 kg m/s (momentum).

Ya, the easy shortcut is that you don't have to remember the formulas if you remember the units. 

Velocity unit is m/s

Mass unit is kg

Force unit (N) is kg*m/s^2

Power unit (W) is kg*m/s^3

Acceleration unit is m/s^2

Torque unit is N*m which is kg*m/s^2*m which is kg*m^2/s^2

etc. etc. etc.

 

Anyway... once you know the end result, you can figure out which components need to be multiplied / divided to get you there

 

 

Anyway... on topic, I think when people say "torque in a race engine is really important torque torque torque blah blah torque" what they really mean is "there is typically a strong correlation between engines which have high measured torque and engines with a flat-ish power curve. And power is what is actually important. And a flat section at the peak power RPM range is great."

Edited December 26, 2021 by enginerd

[mender]

I would have scored a lot higher on my physics tests if I had shown my work.

 

Some popular fallacies:

1. An engine has a narrow power band if the torque peak and the hp peak are less than 1000 rpm apart.

2. I think this is related to people believing that the ideal shift point will have the engine at or very near the torque peak after the shift.

3. As a result, these people don't see the sense in going more than a few hundred rpm past the hp peak on the dyno. 

[mender]

Here's a fairly flat hp curve with a very early torque peak (not even on the graph!):

http://dynoplus.com/dyno_engines/2009/Paul_Lamoureaux/index.htm

 

And another that's similar:

http://dynoplus.com/dyno_engines/2009/Rej_Dejardins/index.htm

 

Then one that's not quite so flat:

http://dynoplus.com/dyno_engines/2009/Chris_Beck/index.htm

 

Then one that needs a close ratio transmission:

 

Always fun figuring out how to get the most out of a particular engine.   

 

[tyler_j]

[Robmink]

On 12/25/2021 at 3:28 PM, wvumtnbkr said:

Not exactly.  Force at the end of a moment arm is measured.  Torque is calculated knowing the moment arm length.

 

So, dynos actually measure force.  Then calculate torque.  Then calculate power.

 

Absolutely correct.

 

Horsepower = (Torque x RPM) / 5,252

 

They are forever linked through RPM. 

Edited December 27, 2021 by Robmink

[Grufton]

On 12/25/2021 at 9:20 PM, hotchkis23 said:

This is why I love these forums, getting to see all the knowledge that members have is awesome!

 

And then there's fluid volume relative to geographic location...

[wvumtnbkr]

3 hours ago, Grufton said:

 

And then there's fluid volume relative to geographic location...

Well, that does change.  Volume of a solid structure does not.  Lolz

[TiredBirds]

In drag racing we say, Torque gets you ot of the hole, HP gets you down the track....

[hotrod]

"Horsepower is how fast you hit the wall. Torque is how far you move it" 

[wvumtnbkr]

4 hours ago, hotrod said:

"Horsepower is how fast you hit the wall. Torque is how far you move it" 

Only if you keep your foot in it and it's geared like a rock crawler!  Lolz.

[mender]

On 1/2/2022 at 9:00 AM, TiredBirds said:

In drag racing we say, Torque gets you ot of the hole, HP gets you down the track....

In road racing, getting out of the hole is pretty low on the "needs" list, but getting down the track is pretty high!

[Fitsbain]

On 12/26/2021 at 4:04 PM, mender said:

I would have scored a lot higher on my physics tests if I had shown my work.

After I found a pattern in one of my professors math questions, I finished the test in 5 minutes with no work shown.

 

The next day he made me do a proof of my approach, which resulted in more work than if id just done it the way he taught us in the first place.

 

[atxe30]

1 hour ago, Fitsbain said:

After I found a pattern in one of my professors math questions, I finished the test in 5 minutes with no work shown.

 

The next day he made me do a proof of my approach, which resulted in more work than if id just done it the way he taught us in the first place.

 

you got a valuable lesson about academia out of that one!!!

[mender]

2 hours ago, Fitsbain said:

After I found a pattern in one of my professors math questions, I finished the test in 5 minutes with no work shown.

 

The next day he made me do a proof of my approach, which resulted in more work than if id just done it the way he taught us in the first place.

 

Yeah, I found shortcuts, too! And my calculus teacher was fine with my method - as long as I showed my work.