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

[soawjo]

I would think, as a physicist, you would be able to reason through it and decide for yourself. But I’m not a physicist, so perhaps I’m overreaching. That’s not a dig. It’s just my naive opinion.

Again, I don’t think he’s wrong about his method and I believe it gets him the correct answer. But that fact that gets the right answer doesn’t exclude other equivalent methods.

I’m happy to retract my statements and apologize for my arrogance if someone can show I’m wrong.

Just to be clear, I’m a physicist by education not by vocation. It’s been about 20 years since I did any serious physics. I mean, earlier in this thread I was getting power and force confused which shows you where I’m at these days. One is a vector and the other is a scalar ffs, I should have my degree taken away from me for that.

I’m just going to take the view that I’ve never designed a power train for a motor vehicle so even though what you’re saying makes sense to me there could very easily be something I’m missing.

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[Jhenson29]

Just to be clear, I’m a physicist by education not by vocation. It’s been about 20 years since I did any serious physics. I mean, earlier in this thread I was getting power and force confused which shows you where I’m at these days. One is a vector and the other is a scalar ffs, I should have my degree taken away from me for that.

I’m just going to take the view that I’ve never designed a power train for a motor vehicle so even though what you’re saying makes sense to me there could very easily be something I’m missing.

Fair enough.

 

[Gwaihir]

30kHz is higher than anything I deal with. I’m usually working with 2 or 3. Sometimes 6 or 8.

What’s driving that need (pun intended)?
Output frequency? Motor thermals?

Did you have a load reactor?
What current?

Sorry for the 20 questions. I just find it interesting.

I was controlling brake system pumps. It was all about keeping continuous motor current, rather than discontinuous As noise was the big problem when you want to have brake blending and need friction help. I was lucky, only needed to go up to 30A. Nothing like a traction motor drive!

 

[Runestone]

I think some of the confusion comes from looking at two different things: the engine and a moving system (the car). In the engine are torque and power directly correlated to each other and, as jhenson29 has pointed out, the power curve can be directly derived from the torque curve and vice versa. That indicates that you could take the torque/force and directly get the acceleration through Newton's second law.

If you look at a moving car, however, you must also fulfill the conservation of energy (first law of thermodynamics). That says the dynamic energy of the car must equal the work done by the engine (neglecting friction losses for now). The power input (P) during a time (t) will result in kinetic energy in a car with mass (m) and speed (v):

P t = m v^2/2

Rearranging this gives (sqrt stands for square root)

v = sqrt(2 P t/m)

Differentiating with respect to t to get acceleration gives (assuming constant power)

a = sqrt(P/2 m t)

This says that the acceleration is directly proportional to the power input. But it also says that acceleration for a given power decreases over time as the speed increases. This even without considering the air drag (which of course adds to the reduction).

A very practical "proof" of the importance of power is to take a car with a manual gearbox and accelerate it while keeping the rpm as close to the max power rpm as possible. Then repeat that with the rev close to max torque rpm. I doubt than anyone in this forum would say that the latter is faster.

So the power gives the most direct estimate of the acceleration of the car.

 

[JimBob]

I think some of the confusion comes from looking at two different things: the engine and a moving system (the car). In the engine are torque and power directly correlated to each other and, as jhenson29 has pointed out, the power curve can be directly derived from the torque curve and vice versa. That indicates that you could take the torque/force and directly get the acceleration through Newton's second law.

If you look at a moving car, however, you must also fulfill the conservation of energy (first law of thermodynamics). That says the dynamic energy of the car must equal the work done by the engine (neglecting friction losses for now). The power input (P) during a time (t) will result in kinetic energy in a car with mass (m) and speed (v):

If the dynamic energy of the car equals the work done by the engine than you could express the P in your equation as Power = Torque * angle traveled / time where the torque and angle traveled are the inputs from the engine. (I think).

This would take you back to which combination of torque and RPM you want to use for engine power.

 

[Runestone]

This would take you back to which combination of torque and RPM you want to use for engine power.

Yes, and the best combination is where torque times rpm is at max, i.e. at max power.

 

[Jhenson29]

I think some of the confusion comes from looking at two different things: the engine and a moving system (the car).

Yes, and I thought about that some yesterday and almost commented again, but decided I was starting (or continuing…) to beat a dead horse, and figured I just leave it alone unless someone commented.

But I agree.

I was always considering the motor and requiring the curves as I thought that was the context.

 

[Avantgarde]

Peak torque and peak power are both basically useless

I can't agree with this. Peak torque is useless in telling the capability of an engine. Peak power may not tell the full story about an engine but it still tells you what the engine is capable of. As long as an engine produces a certain amount of power, even if that power comes in a narrow band it can be transmitted to the wheels and converted to performance with the proper transmission application. Even if the power band is ultra narrow, a CVT transmission for example can very effectively deliver that power to the wheels, the engine would stay at its sweet spot in terms of RPM and CVT would keep shrinking its ratio to accelerate the car.

 

[Jhenson29]

I can't agree with this.

Ok. Then don’t.

Edit: I’ll concede that a peak power can tell you a potential in a way that peak torque can not, but it still does you no good unless you utilize it and in any case you will still always have to know RPM, which then goes back to my numerous previous posts which I won’t repeat (for everyone’s sake).

So, maybe “equally” useless is too much. I’ll go with “nearly equally” useless.

Which you may still disagree with, but really, consider the difference in usefulness of individual power and torque numbers relative the difference between the usefulness of them relative to the curves.

 

[JimBob]

As long as an engine produces a certain amount of power, even if that power comes in a narrow band it can be transmitted to the wheels and converted to performance with the proper transmission application.

This should be qualified. The engine has to be designed from the get go for the use for which it is intended. There are cases where you want an engine with high torque. An F1 engine generates more horsepower than a caterpillar D11T, 1000 vs 850, but would never work in that application. It doesn't have the torque. 260 lb-ft @ 16000 RPM vs 3899 lb-ft @ 1200 RPM. You can't effectively gear a low torque high RPM engine to make it a high torque low RPM engine.

 

[Jhenson29]

An F1 engine generates more horsepower than a caterpillar D11T, 1000 vs 850, but would never work in that application. It doesn't have the torque. 260 lb-ft @ 16000 RPM vs 3899 lb-ft @ 1200 RPM.

260lb-ft@16000rpm is only 792HP though…?

But that aside, assuming the same power, what prevents you from gearing it to give you the same torque@speed final output?

 

[JimBob]

260lb-ft@16000rpm is only 792HP though…?

But that aside, assuming the same power, what prevents you from gearing it to give you the same torque@speed final output?

I should be more precise.

The F1 engine I referred to, is a hybrid engine where the electric motor adds about 200hp according to what I found. Your torque number then lines up nicely.

With respect to the gearing. It's been about 50 years since I had any courses in statics and dynamics and gears weren't part of it but let's see what I can do.

There are high RPM motors which can be used where a lot of torque is required. A gas turbine for example. Electric motors are good as they can have high RPM and depending on the strength of the magnetic field can generate high torque.

In many applications a lot of torque is required at low RPM, so you will need a complex gear box to get this from a high RPM motor. The proof is that they don't build D11's with F1 engines. They use engines with big cylinders and pistons that consume a lot of fuel.

Just because you can theoretically do it, doesn't mean it makes sense.

You design the motor for the application.

 

[Avantgarde]

This should be qualified. The engine has to be designed from the get go for the use for which it is intended. There are cases where you want an engine with high torque. An F1 engine generates more horsepower than a caterpillar D11T, 1000 vs 850, but would never work in that application. It doesn't have the torque. 260 lb-ft @ 16000 RPM vs 3899 lb-ft @ 1200 RPM. You can't effectively gear a low torque high RPM engine to make it a high torque low RPM engine.

If by “effectively” you mean “efficiently” i’d agree. But in terms of delivering the required power with proper gearing an f1 engine could move a CAT. It would be a very expensive CAT and also one with crazy fuel consumption. “It does not have the torque” - this fallacy is exactly what we are trying to explain up above. the problem with the application would not be “the peak torque not being enough”. As long as the engine produces sufficient power, low torque - high RPM configurations can be geared to move heavy vehicles at the same or very similar speed. CVT transmissions were used in tanks, locomotives in the past. Problems would be due to reliability, efficiency etc. not due to “low torque”

 

[JimBob]

Yes I do mean efficiently. To quote Archimedes, "Give me a lever long enough and a place to stand and I can move the world". For that to work he has to find a lever long enough and a place to stand". At some point It becomes a theoretical argument rather than a solution.

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