Power to weight ratio or High performance

[JD]

You bodys power output = Car HP
The weight of the shovel lifted = Car's Torque
Number of lifts per min = Cars engine RPM
The work or effort require to accelarate the car = The amount of sand.
The sand falling through the glass = Friction (Wind, gears etc..)
The amount of sand in the top = Cars current speed

As a Human you can vary your shovel weight.

You need to shovel 1 metric tonne of sand from the bottom of an hourglass to
the top, the more sand in the top the faster it falls through to the bottom,
with one tonne of sand in the top the sand falls through at 30kgs per min.
Your bodys power output is fixed. Using a small shovel you can shift 1 kg
with each lift and you can do this fast say 30 lifts/min (30kgs/min). With
the large shovel you can lift 10kgs but it takes you longer to do this
(3lifts per min). When the hour glas is full you can only maintain the
amount of sand in there NOT add to it. If you wanted to add more you need
more power.

If you doubled the power output but kept the shovels the same you could lift
1 kg 60times/min or 10 kg 6 times/min, this getting to a full top of the
hour glass (accelaration) quicker. youd also be able to cope with 60kgs of
sand falling through per min.

Which is to say, a higher top speed assuming you aren't redline-limited.

 

[JD]

While you fellows discuss this, take into consideration:
* Torque is a force around a rotating axis.
* HP is a mathematical calc taking force, time & distance into
consideration. 33,000 ft-pounds per min.

Additionally torque and kilowatts aren't related. One is force the
other is a quantity of power. One kw = 1.34 HP

Mickey

They most definitely are related.
Torque = NM (Newton Meters) = KG x M^2/sec^2
Watt = KG x M^2/sec^3 = NM/sec
KW = 1000 Watts.

 

[JD]

"Cam Penner"

... but torque IS related to HP. It is calculated
mathematically by combining the RPM, the torque and a
constant.

As is torque and power or NM and KW

 

[Cam Penner]

Also, we don't worry about gas prices like they do.

This is likely the largest reason.

Because European speeds are higher on the highway, acceleration from a high
speed to a higher speed is more important than acceleration from a standing
stop and lighting up your tires. While it is still torque converted to
power, low-end torque is not as important as higher-end torque. So, KW at

This is more a matter of gear selection than location of
torque. Put the engine in the RPM range of the meat of the
HP curve, and torque doesn't matter. On an engine with low
torque and high HP, this means having a shorter first gear.

higher RPM is great for what they do with their cars; in Imperial or US
measurements, that equates to HP. But my point was, in the original post,
that torque, not HP is what an engine operates on, and since HP is really
just a calculation of torque for a given RPM, we can't look solely at HP
numbers to determine how high a performer a car really is (discounting what
it actually means to be a high performer).

Completely true. Gear ratios combined with the HP curve do
a much better job than the HP curve alone. The key to
performance is to keep the car in the meat of the HP curve
at all times.

But, I agree that it does influence the type of engines that sell well. In
N. America (except for motorcycle enthusiasts who know the difference) a
big-assed displacement engine that revs low with gobs of low-end grunt and a
transmission the size of a cattle barn, seems to reign supreme, while
small-displacement, high-revving engines are king everywhere else.

As a person with both a "high torque" engine and a "low
torque" engine in my garage, I can certainly appreciate the
differences in characteristics of the vehicles. But in
both cases, for maximum performance, I need to maximize HP
at the transmission input, and use the gears to maximize
the torque at the wheels.

 

[y_p_w]

But you don't know the power unless you know the revs since HP varies with
RPM the same as torque; because it is calculated as a function of torque and
RPM.




It does not change the fact that the instantaneous force applied by a
crankshaft, or the power measured over time, is rotational energy in a car;
torque. Since the engine only produces torque as useful output (it produces
heat, chemical emissions, etc. but these are not useful outputs per se),
then everything else you measure about the engine is derived from torque.

What the heck is "rotational energy"? The inertial mass of the
crankshaft is too small to act as a flywheel. Torque alone doesn't
tell you squat about how much energy is being produced by the engine.

Personally I don't particularly like the terms "high torque" or
"low torque" engine because they don't really describe the true
nature of the engine. I'd think "high grunt" and "high revving"
are better terms. A "high grunt" (your typical large displacement
[possibly diesel] engine) would produce more torque (and thus power)
at lower revs. This would be better suited towards automatic
transmissions and/or hauling large loads, since they can produce
adequate (but not peak) power at lower revs.

OK. So you don't like the terms. What I mean by 'high-torque' is an engine
which produces the majority of its torque at low RPM, while a high HP engine
is one that either produces very little torque at low RPM and higher torque
at high RPM, or maintains its low torque well past its peak; like an F1
engine.

There are all sorts of engines. Whenever you talk about the "torque"
of an engine at the crankshaft, the term is meaningless unless you
know the revs. Once you have that you know the power output. If
engine A produces twice the torque at 2000 RPM than engine B, that
means it's producing twice the power at 2000 RPM than engine B. My
biggest beef is those who think a single peak power or torque figure
is adequate to describe the acceleration of a car. It's far more
complicated than that.

And it's impossible to maintain torque past the power peak. Look at
any power/torque curve, and the power always peaks at higher revs
than the torque peak.

Knowing the power at the crankshaft (without knowing anything else
except the weight) gives a decent indication of acceleration.
Knowing the torque at the crankshaft indicates nothing unless you
know what revs, what gear, and the weight of the vehicle.

 

[JD]

torque.

What the heck is "rotational energy"? The inertial mass of the
crankshaft is too small to act as a flywheel. Torque alone doesn't
tell you squat about how much energy is being produced by the engine.

Torque. The engine's power take-off is essentially the end of the
crankshaft, which is spinning. Consequently, that is where you measure the
output of the engine; torque.

Personally I don't particularly like the terms "high torque" or
"low torque" engine because they don't really describe the true
nature of the engine. I'd think "high grunt" and "high revving"
are better terms. A "high grunt" (your typical large displacement
[possibly diesel] engine) would produce more torque (and thus power)
at lower revs. This would be better suited towards automatic
transmissions and/or hauling large loads, since they can produce
adequate (but not peak) power at lower revs.

OK. So you don't like the terms. What I mean by 'high-torque' is an engine
which produces the majority of its torque at low RPM, while a high HP engine
is one that either produces very little torque at low RPM and higher torque
at high RPM, or maintains its low torque well past its peak; like an F1
engine.

There are all sorts of engines. Whenever you talk about the "torque"
of an engine at the crankshaft, the term is meaningless unless you
know the revs. Once you have that you know the power output. If
engine A produces twice the torque at 2000 RPM than engine B, that
means it's producing twice the power at 2000 RPM than engine B. My
biggest beef is those who think a single peak power or torque figure
is adequate to describe the acceleration of a car. It's far more
complicated than that.

It isn't enough. However, neither is HP. HP varies with RPM as well. To
state what the peak HP is still not sufficient to tell you much of anything
without knowing what RPM the peak HP is, and what gears it is married to.

And it's impossible to maintain torque past the power peak. Look at
any power/torque curve, and the power always peaks at higher revs
than the torque peak.

Many high performance engines have very flat torque curves and will maintain
something close to peak torque well past the peak; ie the torque drops off
slowly after the peak.

Knowing the power at the crankshaft (without knowing anything else
except the weight) gives a decent indication of acceleration.

It does not.

Knowing the torque at the crankshaft indicates nothing unless you
know what revs, what gear, and the weight of the vehicle.

Same for HP.

 

[JD]

"Cam Penner"

This is likely the largest reason.
at

This is more a matter of gear selection than location of
torque. Put the engine in the RPM range of the meat of the
HP curve, and torque doesn't matter. On an engine with low
torque and high HP, this means having a shorter first gear.


Completely true. Gear ratios combined with the HP curve do
a much better job than the HP curve alone. The key to
performance is to keep the car in the meat of the HP curve
at all times.


As a person with both a "high torque" engine and a "low
torque" engine in my garage, I can certainly appreciate the
differences in characteristics of the vehicles. But in
both cases, for maximum performance, I need to maximize HP
at the transmission input, and use the gears to maximize
the torque at the wheels.

Agreed.

 

[TG]

I don't even know what the skid numbers were stock but I added Tien HA
coilovers and stickier tires and I get a consistent reading of 1.1G. I have
never launched hard and never will...too easy to break things with that much
traction but I do drive fast and hard on occasion.
I could only afford a 12 year old VR-4...but it only has 59,000 miles on
it and is real sweet, love the four wheel steering and limited slips.
I also added a K&N FIPK and Magnaflow catback with gutted cats and Stillen
downpipe...runs good even with stock boost, but with it cranked up a bit
....WOW! TG

 

[JD]

I don't even know what the skid numbers were stock but I added Tien HA
coilovers and stickier tires and I get a consistent reading of 1.1G. I have
never launched hard and never will...too easy to break things with that much
traction but I do drive fast and hard on occasion.
I could only afford a 12 year old VR-4...but it only has 59,000 miles on
it and is real sweet, love the four wheel steering and limited slips.
I also added a K&N FIPK and Magnaflow catback with gutted cats and Stillen
downpipe...runs good even with stock boost, but with it cranked up a bit
...WOW! TG

No speed limiter on the Canadian STi. On a runway, we had mine turning a
little less that 6900 in sixth gear. It was limited by drag, and the window
seals were screetching from the wind coming off of the side mirrors. My
buddy is a highway cop and his static radar recorded a speed of 269 KPH. We
then calculated the speed based on the tire diameter, the final drive ratio
and 6900 RPMs. It works out to 271.24 KPH or 163.23 MPH. So we got it up
to a little less than 163 MPH.

 

[y_p_w]

Torque. The engine's power take-off is essentially the end of the
crankshaft, which is spinning. Consequently, that is where you measure the
output of the engine; torque.

No, no, no. Torque is a "static" variable. It has no time component.
All it tells is the amount of work that can be done per unit of
angular displacement. In English units (man how I hate them):

1 ft-lb is equivalent to the force of 1 lb of gravity acting on a 1 ft
lever. Work (energy produced) from a constant force is defined as:

work = force * distance force is applied.

The distance with that 1 ft lever is the circumference of the circle
at the edge of the lever (where the force is applied). So the amount
of work done with 1 ft-lb for one revolution is:

work = 1 lb * (2*pi * 1 ft)

You can apply force or torque to something that isn't moving (like a
rusty bolt). Until it starts moving, no work is being done even
though torque is more than 0.

Personally I don't particularly like the terms "high torque" or
"low torque" engine because they don't really describe the true
nature of the engine. I'd think "high grunt" and "high revving"
are better terms. A "high grunt" (your typical large displacement
[possibly diesel] engine) would produce more torque (and thus power)
at lower revs. This would be better suited towards automatic
transmissions and/or hauling large loads, since they can produce
adequate (but not peak) power at lower revs.


OK. So you don't like the terms. What I mean by 'high-torque' is an

engine

which produces the majority of its torque at low RPM, while a high HP

engine

is one that either produces very little torque at low RPM and higher

torque

at high RPM, or maintains its low torque well past its peak; like an F1
engine.

There are all sorts of engines. Whenever you talk about the "torque"
of an engine at the crankshaft, the term is meaningless unless you
know the revs. Once you have that you know the power output. If
engine A produces twice the torque at 2000 RPM than engine B, that
means it's producing twice the power at 2000 RPM than engine B. My
biggest beef is those who think a single peak power or torque figure
is adequate to describe the acceleration of a car. It's far more
complicated than that.

It isn't enough. However, neither is HP. HP varies with RPM as well. To
state what the peak HP is still not sufficient to tell you much of anything
without knowing what RPM the peak HP is, and what gears it is married to.

Sure. torque and power vary in a fixed relationship as long as the
engine is moving. What I'm saying is that knowing what the power
output at the crankshaft at any given instant (without knowing much
else) gives a good first order approximation of how quickly energy is
being turned into kinetic energy (E=0.5m*v^2). That's what power is -
how much energy is being produced per unit time. Torque at the
crankshaft at any given instant doesn't say squat.

Many high performance engines have very flat torque curves and will maintain
something close to peak torque well past the peak; ie the torque drops off
slowly after the peak.

I used to own a 1995 Acura Integra GS-R. The sucker redlined at 8000
RPM. There was a power/torque curve in the brochure. The torque
curve was flat from about 3000 RPM (~120 ft-lbs) to the torque peak
at about 6800 RPM (130 ft-lbs). It tailed off a little and dropped
quickly by the time it hit the redline. The power peak was just short
of the redline. This kind of high-revving engine has a relatively flat
torque up to the peak, which then drops quickly to about 100 ft-lbs
at redline.

This guy has some power/torque curves for his 1995 Honda Civic SiR:

It does not.




Same for HP.

No - if you know how much power is being produced at the crankshaft,
you have a reasonable indication (there are frictional losses) of
the rate at which energy is being converted into kinetic energy.

Power at the crankshaft becomes torque at the wheels which turns into
force at the contact patch - more or less. It's not a linear
correlation to the F=ma equation, but it better than knowing torque
at the crankshaft alone.

 

[JD]

No, no, no. Torque is a "static" variable. It has no time component.
All it tells is the amount of work that can be done per unit of
angular displacement. In English units (man how I hate them):

You don't need a time component because you are measuring the potential
work. HP is still calculated from torque for a car. Consequently, if
torque is varying, so is HP and vice versa.

At any rate, in english it is lb-ft or force * distance. In SI it is NM or
force * distance

1 ft-lb is equivalent to the force of 1 lb of gravity acting on a 1 ft
lever. Work (energy produced) from a constant force is defined as:

work = force * distance force is applied.

The distance with that 1 ft lever is the circumference of the circle
at the edge of the lever (where the force is applied). So the amount
of work done with 1 ft-lb for one revolution is:

work = 1 lb * (2*pi * 1 ft)

You can apply force or torque to something that isn't moving (like a
rusty bolt). Until it starts moving, no work is being done even
though torque is more than 0.
True

Personally I don't particularly like the terms "high torque" or
"low torque" engine because they don't really describe the true
nature of the engine. I'd think "high grunt" and "high revving"
are better terms. A "high grunt" (your typical large displacement
[possibly diesel] engine) would produce more torque (and thus power)
at lower revs. This would be better suited towards automatic
transmissions and/or hauling large loads, since they can produce
adequate (but not peak) power at lower revs.


OK. So you don't like the terms. What I mean by 'high-torque' is an
engine

which produces the majority of its torque at low RPM, while a high HP
engine

is one that either produces very little torque at low RPM and higher
torque

at high RPM, or maintains its low torque well past its peak; like an F1
engine.

There are all sorts of engines. Whenever you talk about the "torque"
of an engine at the crankshaft, the term is meaningless unless you
know the revs. Once you have that you know the power output. If
engine A produces twice the torque at 2000 RPM than engine B, that
means it's producing twice the power at 2000 RPM than engine B. My
biggest beef is those who think a single peak power or torque figure
is adequate to describe the acceleration of a car. It's far more
complicated than that.

It isn't enough. However, neither is HP. HP varies with RPM as well. To
state what the peak HP is still not sufficient to tell you much of anything
without knowing what RPM the peak HP is, and what gears it is married

to.

Sure. torque and power vary in a fixed relationship as long as the
engine is moving. What I'm saying is that knowing what the power
output at the crankshaft at any given instant (without knowing much
else) gives a good first order approximation of how quickly energy is
being turned into kinetic energy (E=0.5m*v^2). That's what power is -
how much energy is being produced per unit time. Torque at the
crankshaft at any given instant doesn't say squat.

Sure it does. It tells you what the potential work is. HP doesn't tell you
any more since the peak HP could be at very high revs which still gives no
indication of acceleration unless you know the revs, the gearing, and the
weight; same as the torque output.

I used to own a 1995 Acura Integra GS-R. The sucker redlined at 8000
RPM. There was a power/torque curve in the brochure. The torque
curve was flat from about 3000 RPM (~120 ft-lbs) to the torque peak
at about 6800 RPM (130 ft-lbs). It tailed off a little and dropped
quickly by the time it hit the redline. The power peak was just short
of the redline. This kind of high-revving engine has a relatively flat
torque up to the peak, which then drops quickly to about 100 ft-lbs
at redline.

This guy has some power/torque curves for his 1995 Honda Civic SiR:

<http://www.eireann.org/specs.html>

Then what were you talking about above?

No - if you know how much power is being produced at the crankshaft,
you have a reasonable indication (there are frictional losses) of
the rate at which energy is being converted into kinetic energy.

Not if you don't know how fast the engine is turning.

Power at the crankshaft becomes torque at the wheels which turns into
force at the contact patch - more or less. It's not a linear
correlation to the F=ma equation, but it better than knowing torque
at the crankshaft alone.

First of all, I never said anything about knowing torque at the crankshaft
alone. What I said was, that HP is simply a function of torque and RPM.
Dynos do not measure HP, they measure torque at a specific RP and calculate
HP. Then engine rotates. As far as the engine is concerned, there is only
torque and RPM.

 

[y_p_w]

Sure it does. It tells you what the potential work is. HP doesn't tell you
any more since the peak HP could be at very high revs which still gives no
indication of acceleration unless you know the revs, the gearing, and the
weight; same as the torque output.

I didn't say anything about knowing peak power. What I said is that
as long as you know the power at **any given instance** you know the
rate at which energy is being added to the system **at that instant**.
If all you know is the power and torque peaks as well as the weight
of the car, the power figure gives a closer approximation, as long as
the gears are properly chosen for the engine characteristics. Of
course
this isn't always the case, but it's a very rough approximation.

will drops

Then what were you talking about above?

That it does drop. Not to zero, but definitely less than the fat
part of the torque curve.

Not if you don't know how fast the engine is turning.

Sorry - I worded that kind of strange. It should have said "indication
of the rate at which kinetic energy is being added to the system". If
you told me that an engine is producing 150 HP at any given instant, I
can tell you that it's adding energy to the system at the rate of
111.9 kilijoules per second (minus frictional losses). I don't need to
know the gear it's in, the engine speed, the car's speed, or the weight
of the car. Of course there are all sorts of frictional losses, such
as wind resistance, tire rolling resistance, transmission losses. Much
of any engine's crankshaft output goes towards making heat, noise, and
vibrations that don't make the car go faster (or that keeps it from
slowing down).

First of all, I never said anything about knowing torque at the crankshaft
alone. What I said was, that HP is simply a function of torque and RPM.
Dynos do not measure HP, they measure torque at a specific RP and calculate
HP. Then engine rotates. As far as the engine is concerned, there is only
torque and RPM.

Of course. However - torque at the crankshaft (i.e. the published
"torque
figure" in the specs) is one of those nebulous things that say little
about how quickly a car can get up to speed. Power at the crankshaft
tells a whole lot more. All I've said is that if **ALL** you know is
the power and torque numbers at any given instance, the power gives a
considerably better indication of engine performance.

 

[y_p_w]

Of course. However - torque at the crankshaft (i.e. the published
"torque
figure" in the specs) is one of those nebulous things that say little
about how quickly a car can get up to speed. Power at the crankshaft
tells a whole lot more. All I've said is that if **ALL** you know is
the power and torque numbers at any given instance, the power gives a
considerably better indication of engine performance.

Actually - if I'm given both torque and power at any given instant,
I should be able to plug it into the power/torque equation and
figure out what the rev rate is.

 

[Mickey]

... but torque IS related to HP. It is calculated
mathematically by combining the RPM, the torque and a
constant.

Did you not read my post completely? The force mentioned is torque
for rotating engines/motors but a calc for determining HP (work,
energy expended over time and distance) isn't limited to rotational
forces.

Mickey

 

[y_p_w]

Did you not read my post completely? The force mentioned is torque
for rotating engines/motors but a calc for determining HP (work,
energy expended over time and distance) isn't limited to rotational
forces.

Here's the thing that gets to me. The torque number at the crankshaft
(i.e. the number in the spec sheet or on the graphed torque curve) has
no direct correlation to any kind of output at the wheels. Power at
the crankshaft (minus frictional losses) has a direct correlation with
output at the wheels. Power is the rate at which energy is output by
the engine. The higher this rate (aka "Power") of producing energy,
the faster a car accelerates. It's that simple. Now getting to the
point where the most power is available is a different matter.

When anyone says that engine A has 1.5 times the torque of engine B at
X RPM, all that means is that engine A also has 1.5 time the power of
engine B at X RPM. The so-called "high-torque at lower RPM" engines
simply produce relatively more power at lower revs than engines with
lower torque at those revs, alhtough this power is going to be less
than the peak power output. Crankshaft power and torque are always
linked. However - crankshaft power can be directly linked to force
at the tire contact patch. Crankshaft torque is meaningless unless
one knows the rev rate.

 

[JD]

I didn't say anything about knowing peak power. What I said is that
as long as you know the power at **any given instance** you know the
rate at which energy is being added to the system **at that instant**.
If all you know is the power and torque peaks as well as the weight
of the car, the power figure gives a closer approximation, as long as
the gears are properly chosen for the engine characteristics. Of
course
this isn't always the case, but it's a very rough approximation.


That it does drop. Not to zero, but definitely less than the fat
part of the torque curve.


Sorry - I worded that kind of strange. It should have said "indication
of the rate at which kinetic energy is being added to the system". If
you told me that an engine is producing 150 HP at any given instant, I
can tell you that it's adding energy to the system at the rate of
111.9 kilijoules per second (minus frictional losses). I don't need to
know the gear it's in, the engine speed, the car's speed, or the weight
of the car. Of course there are all sorts of frictional losses, such
as wind resistance, tire rolling resistance, transmission losses. Much
of any engine's crankshaft output goes towards making heat, noise, and
vibrations that don't make the car go faster (or that keeps it from
slowing down).

And if you know how much HP the engine is producing at any moment in time,
then you also know its RPM at that same moment in time.

Of course. However - torque at the crankshaft (i.e. the published
"torque
figure" in the specs) is one of those nebulous things that say little
about how quickly a car can get up to speed. Power at the crankshaft
tells a whole lot more. All I've said is that if **ALL** you know is
the power and torque numbers at any given instance, the power gives a
considerably better indication of engine performance.

But not car performance.

 

[JD]

Actually - if I'm given both torque and power at any given instant,
I should be able to plug it into the power/torque equation and
figure out what the rev rate is.

Yup. And if you are given the torque and RPM, you can figure out the HP,
and HP as well as REPM, you can figure out the torque; because they are all
related.

 

[JD]

I didn't say anything about knowing peak power. What I said is that
as long as you know the power at **any given instance** you know the
rate at which energy is being added to the system **at that instant**.
If all you know is the power and torque peaks as well as the weight
of the car, the power figure gives a closer approximation, as long as
the gears are properly chosen for the engine characteristics. Of
course
this isn't always the case, but it's a very rough approximation.

Which means you know the RPM and, hence, torque... since HP is calculated
from torque and RPM.

That it does drop. Not to zero, but definitely less than the fat
part of the torque curve.


Sorry - I worded that kind of strange. It should have said "indication
of the rate at which kinetic energy is being added to the system". If
you told me that an engine is producing 150 HP at any given instant, I
can tell you that it's adding energy to the system at the rate of
111.9 kilijoules per second (minus frictional losses). I don't need to
know the gear it's in, the engine speed, the car's speed, or the weight
of the car. Of course there are all sorts of frictional losses, such
as wind resistance, tire rolling resistance, transmission losses. Much
of any engine's crankshaft output goes towards making heat, noise, and
vibrations that don't make the car go faster (or that keeps it from
slowing down).

So, how does that tell you anything about the car's performance, or its
potential performance?

 

[y_p_w]

And if you know how much HP the engine is producing at any moment in time,
then you also know its RPM at that same moment in time.

Not necessarily. Suppose I have no knowledge of: the car in question,
what speed it's currently travelling, or what rev rate it's running at.
If you tell me the engine is outputting 150 HP at a given instant,
it's still trasferring energy to the car at the rate of 111.9
kilijoules/sec, regardless of engine speed. It could be at 2000/3000/
4000/10,000/100,000/etc RPM, and the rate at which energy is added to
increase speed and/or offset parasitic losses would be the same.
That's what power is - the rate that energy is made available in one
form or another.

I'll keep on saying that knowing torque at the crankshaft, devoid of
knowing other factors (rev rate), will not tell how much energy is
being transferred from the engine to the rest of the car. Knowing
the power output at the crankshaft, devoid of knowing other factors,
does indicate the rate of energy being transferred to the rest of the
car.

 

[JD]

Not necessarily. Suppose I have no knowledge of: the car in question,
what speed it's currently travelling, or what rev rate it's running at.
If you tell me the engine is outputting 150 HP at a given instant,
it's still trasferring energy to the car at the rate of 111.9
kilijoules/sec, regardless of engine speed. It could be at 2000/3000/
4000/10,000/100,000/etc RPM, and the rate at which energy is added to
increase speed and/or offset parasitic losses would be the same.
That's what power is - the rate that energy is made available in one
form or another.

I'll keep on saying that knowing torque at the crankshaft, devoid of
knowing other factors (rev rate), will not tell how much energy is
being transferred from the engine to the rest of the car. Knowing
the power output at the crankshaft, devoid of knowing other factors,
does indicate the rate of energy being transferred to the rest of the
car.

So? It still gives zero indication as to the performance of the car