Torque wins

[Alastor]

Originally Posted by LeonOfTheDead

are you considering power at the wheel though?
a car with 300 hp can't perform the same acceleration ignoring what gear is in. I would like to know how that is possible, and still can't agree with you.

Yes, I am definitely talking about power at the wheel because what happens at the wheel is really what matters.

Lets say we have 300 hp and 300 lb-ft of torque at the engine. Now lets say we have a transmission that has an overall gear ratio of 10:1. The result is as follows:

@Engine
300 HP & 300 lb-ft @ 5252 RPM

@Wheel
300 HP & 3,000 lb-ft @ 525.2 RPM

Ignoring any losses (i.e. friction) the gears do not change power. Instead they multiply (10x in this case) the torque. However, the trade off is that speed must be reduced my the same amount (1/10 in this case).

Low power means either high torque or high speed. High power means both high torque and high speed. Think of low power as spinning the tire in first gear, and high power as spinning the tire in 1st, 2nd, and 3rd gear.

Originally Posted by LeonOfTheDead

IMO the power delivering is affected by tires radius and gearing. because since you have a rotational movement (the tire), which deliver a certain power, to convert in a linear move (the car) this involve the dimension of the tire. as far as regard the gar, it's because we are transferring the movement between gears with different dimensions, this implies differences between different gears. a bigger gear would require more power/torque to be moved and that would affect the delivery.

Frictional and inertial losses are a different issue. I don’t disagree with what you are saying but they just complicate an already complicated topic. For the basic discussion of power and torque lets leave those real work complication out, until we agree on the basics.

[LeonOfTheDead]

Originally Posted by henk4

Care to elaborate on that? I always thought that an engine had one power and torque curve (which you see presented in good road tests) and what changes is the position ON the curve and not the curve itself.....

what I was saying is that the power (or torque) curve is made with all the values of the power you have at their respective rpm's values. so there is just one curve, as you said and it's what we are used to see after a test. but that graph is made flooring the accelerator, so with the 100% of load. using a lower load would result in a curve with generally lower values, because the combustion process and so the delivery of power are affected by this modularity. engines (petrol ones, but even diesel ones) are usually more efficient at higher rpm. That's why bigger engines deactivates cylinders at lower rpm.
I explain: being less efficient means two things, higher fuel consumption for the required level of performance, and higher pollutant emissions. deactivating some cylinders (usually 4 in a V8 and 6 on a V12, just because those engine are still balanced in those configurations), the engine is bound the raise the rpm to develop the same performance, becoming more efficient, so less gas-guzzler and more clean. the same can be applied to turbocharged engines, usually smaller ones as the new 1,4 liter form Fiat.

Originally Posted by Alastor

Yes, I am definitely talking about power at the wheel because what happens at the wheel is really what matters.

Lets say we have 300 hp and 300 lb-ft of torque at the engine. Now lets say we have a transmission that has an overall gear ratio of 10:1. The result is as follows:

@Engine
300 HP & 300 lb-ft @ 5252 RPM

@Wheel
300 HP & 3,000 lb-ft @ 525.2 RPM

Ignoring any losses (i.e. friction) the gears do not change power. Instead they multiply (10x in this case) the torque. However, the trade off is that speed must be reduced my the same amount (1/10 in this case).

Low power means either high torque or high speed. High power means both high torque and high speed. Think of low power as spinning the tire in first gear, and high power as spinning the tire in 1st, 2nd, and 3rd gear.



Frictional and inertial losses are a different issue. I don’t disagree with what you are saying but they just complicate an already complicated topic. For the basic discussion of power and torque lets leave those real work complication out, until we agree on the basics.

I guess I got your point.
but, backing on topic, what would you consider to be the right parameter to use for the global level of performance that a car can develop?
IMO, there isn't a single one, or it would be too much far away from reality to reduce the whole problem to this factor. I would say the power/weight ratio could be a good candidate, but at the point someone would say torque/weight...

[Alastor]

Originally Posted by LeonOfTheDead

I guess I got your point.
but, backing on topic, what would you consider to be the right parameter to use for the global level of performance that a car can develop?
IMO, there isn't a single one, or it would be too much far away from reality to reduce the whole problem to this factor. I would say the power/weight ratio could be a good candidate, but at the point someone would say torque/weight...

I would agree there no single factor that can describe true vehicle performance. However, the simplest approach that most often works, IMO, is power-to-weight. You can use the power-to-weight ratio to quickly evaluate the performance between two different cars. It basically represents that absolute best performance the car is capable of. Then things like aerodynamics, gear ratios, power band shape, tires, suspension, etc can be evaluated keeping in mind that they all typically end up reducing the actual performance.

Someone might say torque/weight but again torque is only as useful as the speed it is created at. So torque/weight doesn’t really mean anything.

[LeonOfTheDead]

Originally Posted by Alastor

I would agree there no single factor that can describe true vehicle performance. However, the simplest approach that most often works, IMO, is power-to-weight. You can use the power-to-weight ratio to quickly evaluate the performance between two different cars. It basically represents that absolute best performance the car is capable of. Then things like aerodynamics, gear ratios, power band shape, tires, suspension, etc can be evaluated keeping in mind that they all typically end up reducing the actual performance.

Someone might say torque/weight but again torque is only as useful as the speed it is created at. So torque/weight doesn’t really mean anything.

yep, we finally agree

[Falcon500]

Originally Posted by fisetdavid26

You shouldn't be offended Pieter. I was watching Top Gear and saw Clarkson do the Hitler salute when talking about making a car quintessentially German, and I thought it was funny.

Its a touchy subject and one clarkson takes very lightly.

When over in germany it is illegal to even do the salute and you will get arrested and you will need to prove that there was no political meaning behind it or get charged.

I sorry to say its not funny in the slightest and its one of the many reason I dislike clarkson i also dislike what he says about asins he always goes for lame sterotypes and is just plain offensive.

[dsmerritt]

This is a classic misunderstanding, common if you didn't take physics.

Torque is a motive force. It can be linear or circular. You apply the force to do work, in this case moving something. Power is a measurement of how much work you do. So the more you apply your force in a given length of time, the more work you do. That is why an engine that generates 300 lb/ft of torque at 3000 rpm is making half as much horsepower as an engine that is making 300 lb/ft at 6000 rpm. It's applying the torque twice as much in a given time.

So what counts is the most torque over the rpm range you actually use. An engine that makes lots of horsepower at high speed will lose at low speed to an engine that makes more power at low speed. Similarly, if you can use the high rpm, an engine that makes less peak torque can still accelerate the car faster if if makes that torque at a high enough rpm. It's applying the lesser torque more often.

Torque applied produces power to do work. An electric motor at a stop produces maximum torque but does no work even though it is expending energy, since nithing is moving.

I've been reading these mindless discussions for many years. I blame them on the idiot magazine writers who took jounalism instead of physics.

I'm looking forward to having someone argue with me about this. You're wrong, this is the way it is. Anything else is nonsense, no matter how fervently you believe it.

David Merritt

[LeonOfTheDead]

Originally Posted by dsmerritt

This is a classic misunderstanding, common if you didn't take physics.

Torque is a motive force. It can be linear or circular. You apply the force to do work, in this case moving something. Power is a measurement of how much work you do. So the more you apply your force in a given length of time, the more work you do. That is why an engine that generates 300 lb/ft of torque at 3000 rpm is making half as much horsepower as an engine that is making 300 lb/ft at 6000 rpm. It's applying the torque twice as much in a given time.

So what counts is the most torque over the rpm range you actually use. An engine that makes lots of horsepower at high speed will lose at low speed to an engine that makes more power at low speed. Similarly, if you can use the high rpm, an engine that makes less peak torque can still accelerate the car faster if if makes that torque at a high enough rpm. It's applying the lesser torque more often.

Torque applied produces power to do work. An electric motor at a stop produces maximum torque but does no work even though it is expending energy, since nithing is moving.

I've been reading these mindless discussions for many years. I blame them on the idiot magazine writers who took jounalism instead of physics.

I'm looking forward to having someone argue with me about this. You're wrong, this is the way it is. Anything else is nonsense, no matter how fervently you believe it.

David Merritt

you are considering the engine, and the car, just from the outside. while as you said power and torque are two different entities (but I miss what you mean with linear torque), there are technical reasons behind an engine making its peak of torque at a certain rpm. since power and torque are connected linearly, one could argue that one is "better" than the other, but in the end it doesn't mean anything.
BTW, and electric motor isn't consuming energy (ideally) while the car is standing, but just due to loss. if it isn't working, it can't consume energy, still ideally speaking. as you said, torque can be applied, as a force, to do work. but you need a movement to generate work. work, on the other side, is a way to express energy, so, no work, no energy.

If you have read the whole thread and not just some stupid posts here and there you would have disclosed that some of us have taken physics, and we aren't all wrong as you stated.
besides, I agree this argument is often talked by people who aren't very into the matter.

[Alastor]

Originally Posted by dsmerritt

This is a classic misunderstanding, common if you didn't take physics.

It doesnt matter if you have taken physics or not, it just matters if you understand the physics concepts.

Originally Posted by dsmerritt

You apply the force to do work, in this case moving something. Power is a measurement of how much work you do.

Physics 101 - Force is a measure of Force, Work is a measure of Work, and Power is a measure of Power. These are three different concepts. Applying a Force will not result in work unless it is applied over some distance. So work is a measure of both force and distance. Power is not a measure of work. Power is a measure of the rate at which work is performed.

Originally Posted by dsmerritt

Torque is a motive force. It can be linear or circular.

Statics 101 – torque is special kind of force that causes only rotation. It is never a “linear” force because it always acting along a radius. It can be thought of as the moment of a couple where the non-rotational components of the forces always cancel out (i.e. a pure moment).

[Aloser]

Horsepower = (torque in lb-ft) * ( RPM ) divided by 5,252

You can't have serious horsepower without having serious torque except by running at an insanely high RPM. This is the reason behind the old adage: "There is no replacement for displacement."

I would rather have 100 HP (peak) with an engine which makes 350 lb-ft of torque at 1,500 RPM and declines smoothly to 116 lb-ft at a 4,500 RPM redline than an engine which makes 100 HP(peak) by gradually rising to 100 lb-ft of torque at 5,252 RPM.

The previous example is not entirely fair as an engine with 350 lb-ft of torque at 1,500 RPM is going to be at least a 3 liter, 6 cylinder turbo-diesel while the 100 HP at 5,252 RPM is a typical 1.8 to 2.0 liter, 4 cylinder gasser.

My VW 1.9 literTDI turbo-diesel makes 100 HP peak at 4,000 RPM (~131 lb-ft torque) and 175 lb-ft of torque from 1,800 RPM to 2,400 RPM or 60 HP to 80 HP over the 1,800 to 2,400 RPM range.

The VW 4 1.98 liter cylinder gasser is rated at 115 HP (peak) at 5,200 RPM but has only 122 lb-ft of torque at 2,600 RPM (peak). The gasser is only making 60 HP at 2,600 RPM while the TDI diesel is at 80+ HP and still climbing towards 100 HP at 4,000 RPM. The gasser eventually catches up and makes more horsepower but not until after the diesel has reached its redline.

What it comes down to is the area under the Torque versus RPM curve is what is most important. Peak horsepower, which occurs at only one point on the curve, only determines maximum speed. Torque determines horsepower, driveability and overall performance at every other point on the curve. The perfect torque versus RPM curve is a step function, i.e. rises almost instantaneously off idle to the maximum torque, is nearly flat across as wide of an RPM range as possible and then drops off rapidly at an RPM which is beyond the engine's redline.

How much time do *YOU* spend in a gear at 5,200 RPM before you shift?
I spend almost all of my driving time in my TDI between 1,500 RPM and 2,500 RPM.

[Big time]

Originally Posted by fisetdavid26

Discuss.

Actually torque over a broad rev band wins.

[Aloser]

Originally Posted by Big time

Actually torque over a broad rev band wins.

See previous post:

"What it comes down to is the area under the Torque versus RPM curve is what is most important. Peak horsepower, which occurs at only one point on the curve, only determines maximum speed. Torque determines horsepower, driveability and overall performance at every other point on the curve. The perfect torque versus RPM curve is a step function, i.e. rises almost instantaneously off idle to the maximum torque, is nearly flat across as wide of an RPM range as possible and then drops off rapidly at an RPM which is beyond the engine's redline."