M4 dyno test by Sportauto 465hp/577 nm

[bradleyland]

I can't believe this thread is turning in to a "HP vs torque" argument. Which, for the record, is the dumbest argument since the dawn of the internet. You can't pit torque and horsepower against each other any more than you can pit gallons against inches. "Which is better, gallons or inches?" Anyone asking that question will be laughed out of the room.

Here's the simplest illustration I use to dispatch the "ZOMG torque is what matters" viewpoint:

I can, and have, generated in excess of 250 lb ft of torque with my own body while tightening the nuts on taper fit hydraulic wheel hubs. This is roughly as much torque as the N20 generates in our X3.

Anyone positing that "torque is what matters" must sufficiently explain why I can't simply attach a 1/2"-drive breaker bar to my axle shaft and wrench my way to the grocery store.

The answer you will arrive at is that I cannot generate 250 lb ft of torque at a very high RPM. To which I must immediately refer you to the formula for horsepower: ft-lbs(rpm)/5,252

Eureka! HP is a derivative of torque with rate factored in, which is exactly what we're all trying to understand: how much force does it generate, and at what rate can it do so. If you want to know the rate at which an engine generates force, horsepower is your answer.

[F104]

I think I’ve a decent understanding of metric power/accel etc calculations. Re the BHP/torque discussion it’s really simple. The only thing a tyre understands is torque (or tractive power). If you twist an axle with X torque, that gives X / wheel-radius tractive power. And tractive effort gives then an acceleration F / m (m = mass of vehicle).

Yes there are some driveline losses, rolling tyre losses etc, but torque accelerates a a car. BHP is a mankind invented useless number

However torque curves are too simple too in my view. For my bike (bmw 1200gs) I made these torque/speed curves vs the 1000rr. These show where the torque is vs speed, and for example when to shift (hardly any speed overlap in bike gearing..). These are a bit more complicated, but show very well where each (bike in this case) excel.

[Boss330]

Originally Posted by bradleyland

I can't believe this thread is turning in to a "HP vs torque" argument. Which, for the record, is the dumbest argument since the dawn of the internet. You can't pit torque and horsepower against each other any more than you can pit gallons against inches. "Which is better, gallons or inches?" Anyone asking that question will be laughed out of the room.

Here's the simplest illustration I use to dispatch the "ZOMG torque is what matters" viewpoint:

I can, and have, generated in excess of 250 lb ft of torque with my own body while tightening the nuts on taper fit hydraulic wheel hubs. This is roughly as much torque as the N20 generates in our X3.

Anyone positing that "torque is what matters" must sufficiently explain why I can't simply attach a 1/2"-drive breaker bar to my axle shaft and wrench my way to the grocery store.

The answer you will arrive at is that I cannot generate 250 lb ft of torque at a very high RPM. To which I must immediately refer you to the formula for horsepower: ft-lbs(rpm)/5,252

Eureka! HP is a derivative of torque with rate factored in, which is exactly what we're all trying to understand: how much force does it generate, and at what rate can it do so. If you want to know the rate at which an engine generates force, horsepower is your answer.

That was a great analogy based on the KISS principle of education

[AreOut]

@bradleyland heh in theory you can, it would only take you 5250 minutes instead of one minute with X5

[Boss330]

Originally Posted by F104

I think I’ve a decent understanding of metric power/accel etc calculations. Re the BHP/torque discussion it’s really simple. The only thing a tyre understands is torque (or tractive power). If you twist an axle with X torque, that gives X / wheel-radius tractive power. And tractive effort gives then an acceleration F / m (m = mass of vehicle).

Yes there are some driveline losses, rolling tyre losses etc, but torque accelerates a a car. BHP is a mankind invented useless number

However torque curves are too simple too in my view. For my bike (bmw 1200gs) I made these torque/speed curves vs the 1000rr. These show where the torque is vs speed, and for example when to shift (hardly any speed overlap in bike gearing..). These are a bit more complicated, but show very well where each (bike in this case) excel.

But, as Bradleyland pointed out, it doesn't do you any good unless you can twist the axle with X torque at a certain rate (or rpm). The torque of X of a engine can easily be replicated by a human being using leverage on a lever. But I can't replicate the engines rate of twisting the axle... I could barely do a few RPMs, but I will do the same torque as the engine. Just not at the same rate...

Add the rate and multiply with torque and you have HP. The rate factor (rpm) is a factor that can't be overlooked here...

[Boss330]

Originally Posted by AreOut

@bradleyland heh in theory you can, it would only take you 5250 minutes instead of one minute with X5

And then what was it that made the difference in acceleration???

Oh yeah, the rate (rpm) of the applied torque (or what also results in what we call HP)

[F104]

Originally Posted by Boss330

But, as Bradleyland pointed out, it doesn't do you any good unless you can twist the axle with X torque at a certain rate (or rpm). The torque of X of a engine can easily be replicated by a human being using leverage on a lever. But I can't replicate the engines rate of twisting the axle... I could barely do a few RPMs, but I will do the same torque as the engine. Just not at the same rate...

Add the rate and multiply with torque and you have HP. The rate factor (rpm) is a factor that can't be overlooked here...

That's were the speed comes in, and why i think torque/speed curves show much better what the real situation is.

[AreOut]

well torque*speed of rotating IS the power

Originally Posted by Boss330

And then what was it that made the difference in acceleration???

Oh yeah, the rate (rpm) of the applied torque (or what also results in what we call HP)

of course it is

[Boss330]

Originally Posted by F104

That's were the speed comes in, and why i think torque/speed curves show much better what the real situation is.

Torque X speed is HP...

And HP isn't a useless mankind made number... It's a factor that says how much work a torque producing machine, horse, human can do.

250lb.ft of torque is of little use in a car if it only can apply that torque at the rate of 1rpm. Acceleration would be rather poor... If that torque can be applied at 4000rpm then that engine can do 4000 times more work than the first one. But the torque is still exactly the same... Torque needs rpm's in order to do work (or HP).

[DesertSmokeBBQ]

365-ish WHP?

[CanAutM3]

Originally Posted by Boss330

It's (hp) a factor that says how much work a torque producing machine, horse, human can do.

Not quite. Power represents how fast work can be done . P = W/t

Torque is a rotating force applied. A given amount of torque applied on a given amount of revolutions equates to work. How fast the the revolutions on which the torque is applied are done equates to power.

I am just nitpicking over semantics here, I know you understand the concept better than the majority here .

[CanAutM3]

Originally Posted by F104

I think I’ve a decent understanding of metric power/accel etc calculations. Re the BHP/torque discussion it’s really simple. The only thing a tyre understands is torque (or tractive power). If you twist an axle with X torque, that gives X / wheel-radius tractive power. And tractive effort gives then an acceleration F / m (m = mass of vehicle).

Yes there are some driveline losses, rolling tyre losses etc, but torque accelerates a a car. BHP is a mankind invented useless number.

You are correct, BHP (or power) is a mankind invented number and cannot be directly measured or observed in real life.

However, power still is a very meaningful number.

In the automotive world, power represents the ability of an engine to produce tractive force. The more power an engine produces, the more tractive force it will be able to generate for acceleration.

For example, if an engine produces a rather modest torque output at a relatively high RPM, gearbox de-multiplication will increase the torque at the wheels and the tractive force.

[CanAutM3]

Originally Posted by Boss330

In the metric system power is calculated by the following formula:

P = Torque x 2pi x Rpm

P = Power in watt
Torque is in Nm

Again here, just nitpicking, but you need to convert the minutes into seconds for the formula to work:

P = Torque x 2pi x Rpm / 60

P = Power in watt
Torque is in Nm

[MKE_M3]

I always like to think of it this way. Torque is how hard the push is, Torque times how many pushes you are getting per unit of time is HP.

Imagine your battery died and you want to push start your car. Well, if you have a friend, Boner, that can push (a single moment of push) with twice the force as your other friend, Limpy, but Limpy can push the car twice as often as Boner in a minute, which will accelerate the car faster. I expect they're both generating the same amount of work per unit of time, thus the car would accelerate at the same rate.

Maybe one of the experts could chime in an tell me in which scenario you'd experience greater acceleration?!?!?

[MKE_M3]

If it helps, let's assume the torque is sufficient to move the car from either friend.

[CanAutM3]

Originally Posted by MKE_M3

I always like to think of it this way. Torque is how hard the push is, Torque times how many pushes you are getting per unit of time is HP.

Imagine your battery died and you want to push start your car. Well, if you have a friend, Boner, that can push (a single moment of push) with twice the force as your other friend, Limpy, but Limpy can push the car twice as often as Boner in a minute, which will accelerate the car faster. I expect they're both generating the same amount of work, thus the car would accelerate at the same rate.

Maybe one of the experts could chime in an tell me in which scenario you'd accelerate faster?!?!?

See post #297 for your answer.

[AreOut]

something like that

[MKE_M3]

Originally Posted by CanAutM3

See post #297 for your answer.

Hopefully i fixed it by changing "same amount of work" to "... work per unit of time."

I assume they'd have the same acceleration. I'm legitimately curious. It's been many moons since my last basic physics class .

[swamp2]

Originally Posted by bradleyland

I can't believe this thread is turning in to a "HP vs torque" argument. Which, for the record, is the dumbest argument since the dawn of the internet. You can't pit torque and horsepower against each other any more than you can pit gallons against inches. "Which is better, gallons or inches?" Anyone asking that question will be laughed out of the room.

Although I agree with you in essence, I do also see how folks can get confused. After all if you know either entire curve (torque or power vs. rpm) then you know the other one (that also applies at any given single rpm). In some way they seem almost equivalent in this way (again ignoring the basics that they are much like gallons vs. inches). What is missing of course in this (as I noted earlier) is that if you wanted to do a calculation or simulation of vehicle performance (i.e. know exactly how fast it is), if you begin with the torque curve all of the gearing must also be known. This, by the way, is the most straightforward way to do such a calculation. Thus we arrive at the point of view - hmmm, if I must have and use the entire torque curve to do a calculation, and clearly if I increase torque I directly get more acceleration. Q.E.D. torque is the thing that matters.

Originally Posted by bradleyland

Here's the simplest illustration I use to dispatch the "ZOMG torque is what matters" viewpoint:

I can, and have, generated in excess of 250 lb ft of torque with my own body while tightening the nuts on taper fit hydraulic wheel hubs. This is roughly as much torque as the N20 generates in our X3.

Anyone positing that "torque is what matters" must sufficiently explain why I can't simply attach a 1/2"-drive breaker bar to my axle shaft and wrench my way to the grocery store.

The answer you will arrive at is that I cannot generate 250 lb ft of torque at a very high RPM. To which I must immediately refer you to the formula for horsepower: ft-lbs(rpm)/5,252

Eureka! HP is a derivative of torque with rate factored in, which is exactly what we're all trying to understand: how much force does it generate, and at what rate can it do so. If you want to know the rate at which an engine generates force, horsepower is your answer.

Excellent example.

Not quite technically correct near the end though, the rate of force application (or dF/dt) is not relevant in vehicle performance. Power is the rate of doing work and more work means a larger change in kinetic energy (basically velocity). Thus the rate of change (or rapidity of gain) in velocity (technically energy...) is given by power.

[e39>all]

The only thing that really matters is RPMs, that's why the e92m will always be superior to all future models

[Sedan_Clan]

Originally Posted by e39>all

The only thing that really matters is RPMs, that's why the e92m will always be superior to all future models

You hit the nail on the head sir. That extra 700 or so RPM's just makes a woooorrrlllldddd of difference. Don't forget the sound. The sound makes all of the difference......13 seconds or so slower, BUT....it sure does sound good.

[grimlock]

Originally Posted by bradleyland

I can, and have, generated in excess of 250 lb ft of torque with my own body

"Give me a long enough lever and I can move the world." -Isaac Newton

Perhaps the lever is a good way to illustrate how you can modify torque, and thus torque is not an intrinsic, immutable quality.
Ever use a torque multiplier? These things operate purely mechanically, you just rotate the handle, and for every say 10 revolutions the output is one revolution - BUT at 10* the torque!
How can this be? Ah-ha .. torque is a phantom
Then what is real?

Originally Posted by bradleyland

Anyone positing that "torque is what matters" must sufficiently explain why I can't simply attach a 1/2"-drive breaker bar to my axle shaft and wrench my way to the grocery store.

The answer you will arrive at is that I cannot generate 250 lb ft of torque at a very high RPM. To which I must immediately refer you to the formula for horsepower: ft-lbs(rpm)/5,252

Eureka! HP is a derivative of torque with rate factored in, which is exactly what we're all trying to understand: how much force does it generate, and at what rate can it do so. If you want to know the rate at which an engine generates force, horsepower is your answer.

Yes, like this..

Originally Posted by CanAutM3

You are correct, BHP (or power) is a mankind invented number and cannot be directly measured or observed in real life.

However, power still is a very meaningful number.

This is giving torque too much credit.
The only time it is relevant is when you are talking about the incidental properties of a particular engine, in terms of its torque at what rpm.. which gives you a clearer picture than just the HP it produces.

Originally Posted by MKE_M3

I always like to think of it this way. Torque is how hard the push is, Torque times how many pushes you are getting per unit of time is HP.

Imagine your battery died and you want to push start your car. Well, if you have a friend, Boner, that can push (a single moment of push) with twice the force as your other friend, Limpy, but Limpy can push the car twice as often as Boner in a minute, which will accelerate the car faster. I expect they're both generating the same amount of work per unit of time, thus the car would accelerate at the same rate.

Maybe one of the experts could chime in an tell me in which scenario you'd experience greater acceleration?!?!?

Well in this real life example what would matter is frictional inertia forces - how hard you need to get it moving in the first place.
But, if it is a theoretical situation anyone should be able to move it because the only thing that is preventing it from moving is frictional inertia.
Hence.. you need a better example..

The only thing that would matter is how hard you can push for a brief fraction of a second.. it's not the tour de France


In conclusion, the only intrinsic, basic property of an engine is HP... because force needs to work through distance (in the case of an engine, angular velocity, or RPM).
Because engines are not like a human pushing against a concrete wall, which is pure force, as nothing is moving. I don't even know how hard an engine can push against a wall..
Hence the output of an engine is force through angular velocity (because it spins in a circle), which is HP. Voila. Thank you.

add: However, "torquey" is a descriptive property of engines in that the rpms do not have to be high to produce the HP.
But, you still can't simplify it and just say it produces a lot of torque - you must be meaning that it produces a lot of torque at low rpm.
An engine does not produce torque, it produces power/HP.
YOU can produce torque turning a wrench.
Torque is only one dimension of the two dimension thing called power. (power=force*distance, or HP=torque*rpm)
But it is not a transitivly allowed to talk about only torque in regards to engines.. that would be like saying, my volume is 1.5ft - that is only ONE dimension of your volume. (volume=width*length*height)
'Torque' is like a picture.. but it doesn't tell you anything about the engine if you do not know at what rpm.. you need a MOVIE.. which is HP.