How much HP does a Turbo S REALLY have? Dyno Run Video

[JimBob]

Maybe someone knows or has a good explanation? When researching this, I couldn't find a really good explanation. I can see where the RPM number for a combustion engine comes from. But electric motors have really high RPM's, 15,000-.20,000 RPM. So how does this get input into the dyno?

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[WuffvonTrips]

Maybe someone knows or has a good explanation? When researching this, I couldn't find a really good explanation. I can see where the RPM number for a combustion engine comes from. But electric motors have really high RPM's, 15,000-.20,000 RPM. So how does this get input into the dyno?

I think the x axis shows the dyno's roller rpm in these examples?
EDIT- hang on, in at least one case it is labeled "engine rpm". I assume that to to display engine rpm, data needs to be input for the vehicle-specific gearing and tyre size to derive engine rpm from roller rpm. I don't know what they've done for the Taycan, it seems to show an ICE rev range,

 

[PaulB]

Yes but the whole point of deriving an equation such as this is so commonly used measurements can be put in so it can be done by any mechanic at the dyno. The engine speed readout will be in rpm, the torque in lb-ft

This isn't a case of intellectual refinement it is a practical equation usable by anybody.

I totally agreed with you. Was just trying to help the guy who couldn't see why the units didn't work out!

 

[Jhenson29]

A maximum torque figure by itself does not tell you a thing about capability of an engine if there is no RPM info comes with it.

I would argue that a maximum (peak) power figure by itself does not either. Peak torque and peak power are both basically useless.

On the other hand, a torque curve and power curve are both equally useful.

Sorry, quick aside to prove my point…it’s really common in recoiling and uncoiling applications to have what’s known as wide HP motor. Strip tension (in either case) is generally a constant and for a fixed strip speed, torque and speed are inversely proportional as a coil diameter changes (e.g. large diameter = low speed/high torque; small diameter = high speed/low torque). They’re exactly inversely proportional because they’re both inversely related by the radius. Thus a constant power over a wide speed range (…thus the wide HP motor)

Now, a wide HP motor hits peak HP before full volts (and therefore doesn’t follow the typical electric motor torque curve frequently posted here). This causes the motor to have a much wider constant HP range as it is extended into the section before full volts.

An electric motor with a more typical torque curve would require a much higher peak HP for the application so that it hits the required HP at lower RPM.

This means all electric motors with a typical curve and peak HP between the peak HP of the wide HP motor and the peak HP required by the typical motor are both higher in peak HP and less useable than the wide HP motor for the application.

My point being, it’s the curve and application that matter because that HP is useless when you aren’t using it (truism, but there you go).

 

[Visceral]

While you were discussing the theory of electrical horsepower, the original video disappeared.

 

[Jhenson29]

While you were discussing the theory of electrical horsepower, the original video disappeared.

Same video here if I’m not mistaken.
https://www.taycanforum.com/forum/t...-the-dyno-725hp-continuous-power-output.5576/

 

[rs38]

If an engineer came for a job interview his first question was always “which is important torque or power?”

a good engineer would answer: wheel torque is most important because it directly correlates to vehicle accelleration.

(getting true motor HP on a roll dyno is only possible if you know motor's rpm, know rotational inertia of gearboxes, axes, wheels and you need to be able to put all this in "neutral" and add the drag power of the system)

 

[Jhenson29]

If you know the power curve you can calculate everything else.

If you know the torque curve, you can calculate everything else also though, no?

 

[rs38]

without knowing the gear ratios, you know nothing!

 

[rs38]

I'm sorry, but you simply forgot the gears in your equation (only mentioning engine and chassis above).
What I don't say: power is unimportant, it's of course the main driver in the equation, but it's a bit more complex.
At the end for an optimum acceleration you want to maximize the area under the wheel tourque diagram.

also Porsche knows it

https://www.taycanforum.com/forum/t...n-not-using-launch-overboost.1735/#post-22400

 

[Jhenson29]

Yes, but it is still power that does the work

I’m going to disagree.

Applying a force over a distance does work.
Energy does (or can do, rather) work.

But power is just the rate the work is performed at, and as a result, requires time to do work. It cannot do work on its own. e.g. 100HP for zero seconds is zero work. One may argue that there was never 100HP then, but that’s missing the point. 100HP for one second is not the same work as 100HP for two seconds, if you prefer.

So, as a matter of definition, power does not do work.

At any rate, the whole curve is relevant (not just peak numbers) and at the point the the whole curve is relevant, whether you’re looking at torque or power shouldn’t be relevant as they have a fixed relationship. So, I don’t think it’s about one over the other. If you’re giving precedent to one over the other it’s just because you’re looking at it in a particular way.

As a simple example, let’s say I want to have a car accelerate to 60mph in a given time. At 60mph, the car has some energy.
e = 1/2 * m * v^2
To get the car to that energy, I have to apply an average energy over time such that when multiplied by time to get to 60mph yields that energy. So, this would be average power. But I have to know the actual power curve. Peak power is not sufficient because the acceleration will spend some time at other (possibly) lower points in the curve. In any case, the area under the power curve over time for the acceleration has to equal the energy of the car at 60mph.

Now, let’s do it again another way. I want to accelerate the car to 60mph in a certain time. This will have to be done in some distance.
d = 1/2 * a * t^2
We know time because we said we want this acceleration to occur in a certain time. We know (average) acceleration because we have fixed speed and time.
a = v / t
Therefore,
d = 1/2 * v * t
Okay, so now we have our distance.
Again, the car will have a fixed energy at that speed:
e = 1/2 * m * v^2
To give the car that energy, we have to do work.
w = f * d
We’ve fixed distance, so there is some average force that will need to be applied over that distance. This is proportional to wheel torque (actually, just wheel torque times radius).
Again, similar to power, the peak torque or force doesn’t tell us anything, we need to know the area under the force curve. The area under the force curve applied over some distance has to equal the work required to give the car the energy it will have at 60mph.

Note that I left out additional energy required for losses from drag and rolling resistance as they aren’t relevant to the points. The same principles apply. There is just a counter force to also consider.

So, to do work, you’re either looking at an area of a curve where y is power and x is time or the area of a curve where y is force and x is distance.

To reiterate a previous comment, peak power and peak torque are equally useless while the torque curve and power curve are both equally useful.

 

[Jhenson29]

Why do you make things more complicated than they need to be?

You can derive EVERYTHING engine related you need in order to design the power train of a car from the power curve.

But suit yourself.

….and also the torque curve.

I’m not making anything more complicated. You stated power matters over torque. I showed why that’s wrong.

And why do you think one is more complicated? Because there was more math? That really depends on what you’re trying to do. I recently had to answer some questions for my company’s sales department about energy savings on regen drives vs friction brakes in a particular application. In that application, it was easier to use force and distance than power and time.

in any case, the disagreement was over equivalence, not complexity. Maybe power is always easier for a car. I don’t know. I don’t work in that space. But being easier in a particular application is not the same as being more important.

 

[soawjo]

….and also the torque curve.

I’m not making anything more complicated. You stated power matters over torque. I showed why that’s wrong.

And why do you think one is more complicated? Because there was more math? That really depends on what you’re trying to do. I recently had to answer some questions for my company’s sales department about energy savings on regen drives vs friction brakes in a particular application. In that application, it was easier to use force and distance than power and time.

in any case, the disagreement was over equivalence, not complexity. Maybe power is always easier for a car. I don’t know. I don’t work in that space. But being easier in a particular application is not the same as being more important.

I think @f1eng's point is at the most fundamental level it is power that generates torque not the other way around. No power = no torque. It's like arguing that it's the sun's gravity that is the most important thing in the force that it exerts on the earth. No, it's its mass that is the most important thing, the gravity is a consequence of the mass just as torque is a consequence of power

 

[BigBob]

Why is it that rear spoilers make a car look faster, but actually make them slower?

 

[Jhenson29]

I think @f1eng's point is at the most fundamental level it is power that generates torque not the other way around. No power = no torque. It's like arguing that it's the sun's gravity that is the most important thing in the force that it exerts on the earth. No, it's its mass that is the most important thing, the gravity is a consequence of the mass just as torque is a consequence of power

I think they’re linked in a way that makes that not particularly relevant and which one you would prefer to speak about depends on context rather than an absolute.

And again, because it’s the whole curve that matters, and not any one peak value, and there’s a fixed relationship, I wouldn’t understand the context of one being more important.

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