Technical problem???HELP ME!PLX!

  • Thread starter tony1013
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Why does the torque-engine rotation curve exhibit a parabolic (in which the exact shape, either left or right skewed, is depending on the engine's characterictics) rather than a linear relationship???:dunce:

Please tell me in great detail as possible (probably with mathematical equation) since i haven't figured it so far.:indiff:

Thank you!!!💡
 
Why does the torque-engine rotation curve exhibit a parabolic (in which the exact shape, either left or right skewed, is depending on the engine's characterictics) rather than a linear relationship???:dunce:

Please tell me in great detail as possible (probably with mathematical equation) since i haven't figured it so far.:indiff:

Thank you!!!💡

I can't tell you in great detail as I'm about as far from smart than anybody.. BUT - I can tell you that, depending on state of tune and how it was done, your torque curve will change, but always stay parabolic. The engine has a point where it develops the most torque, the of the parabolic curve, where it'll drops afterwards. Take a phat piece of American Iron, and it's torque curve will be way down the band - add a turbo and it will, because of the way it works, shift the "top" further up the band (More revs, more efficiency)..

No matter what, it'll always be parabolic..

As for Maths - You have to wait for Famine to get here - But he's probably getting silly on some weird black english brew as it's his Bday...
 
Actually, (if I remember correctly,) the maths isn't to bad.

For an engine...

Horsepower = (Torque*RPM)/k

Where k is a constant value depending on the units your torque is in (5252 for ft.lbf, 7124 for Nm). You can easily rearrange that the get...

Torque = (k*Horsepower)/RPM

...from which it's easy to see that torque is affected by both horsepower and output RPM (k is a constant value). Generally horsepower increases as at high revs, which acts to increase torque, but the increased revs by themself bring the value back down. 👍
 
I think he's simply expecting torque to go up with RPM. Of course it doesn't.

Tony, torque is not a mathematical function of anything. It's the result of many factors in engine design, like displacement, stroke, breathing, and so on. At any given RPM, the engine can produce a given amount of torque, and that amount reaches a peak usually somewhere near the top of the engine's rev range, then declines, usually rather sharply. The torque curve of an engine is measured, not calculated.

Horsepower, on the other hand, IS a mathematical function of the torque and engine speed, and the formula has been given in previous posts.
 
Tony, torque is not a mathematical function of anything. It's the result of many factors in engine design, like displacement, stroke, breathing, and so on. At any given RPM, the engine can produce a given amount of torque, and that amount reaches a peak usually somewhere near the top of the engine's rev range, then declines, usually rather sharply. The torque curve of an engine is measured, not calculated.

Horsepower, on the other hand, IS a mathematical function of the torque and engine speed, and the formula has been given in previous posts.
Perfect explanation, +rep for that! 👍
 
Flerbizky, MasterStorm, and wfooshee said pretty much everything there is to be said. 👍 👍 👍

These are the main points that Tony should take away from this thread:

Flerbizky
...depending on state of tune and how it was done, your torque curve will change, but always stay parabolic. The engine has a point where it develops the most torque, the of the parabolic curve, where it'll drops afterwards.
MasterStorm
Horsepower = (Torque*RPM)/k

Where k is a constant value depending on the units your torque is in (5252 for ft.lbf, 7124 for Nm). You can easily rearrange that the get...

Torque = (k*Horsepower)/RPM
wfooshee
I think he's simply expecting torque to go up with RPM. Of course it doesn't.

Tony, torque is not a mathematical function of anything. It's the result of many factors in engine design, like displacement, stroke, breathing, and so on...The torque curve of an engine is measured, not calculated.
 
Torque is provided by the MEP (Mean Effective Pressure) in the cylinders, the MEP is a result of these :

- The amount of air and gas mixture that gets into the cylinders.
- How well this mixture burns.

At low revs the main limiting factor in getting a good MEP is how much mixture gets into the cylinders, at high revs the flame propagation time is another limiting factor.

How much mixture gets in is obviously limited by the area that lets it in when the intake valve opens, it is also limited by the exhaust valve side as exhaust gases have to get out before fresh mixture can get in. It also depends on other things :

The amount of mixture that will get into the cylinders of a naturaly aspirated engine will reach a maximum that depends on air temperature, the length of the intake manifolds, the temperature of the exhaust gases and the length and configuration of the exhaust pipes (for example : 4 in 2 in 1).

When using a turbo-compressor or a compressor the intake pressure will be the main variable driving how much gets in the cylinders. The drawback is that compressing air heats it up and that hot air occupies more space, so if nothing is done to cool it down you will fill your cylinders with less air than is theoreticaly possible. This is why intercoolers are used. The exhaust side also plays a role just like in the naturaly aspirated engine.

How well the mixture burns depends mainly on :

- The shape of the combustion chamber.
- Mixture quality.
- Mixture temperature.

The combustion chamber's shape is supposed to get the mixture as close as possible to the spark plug, otherwise the spark may not ignite the mixture properly.

Given all this the flame will or will not quickly propagate from the plug to the whole mixture. This propagation time is the time it takes for the maximum pressure point to be reached in the cylinder. If during this time the piston has already started going down (high revs + bad mixture for example), the maximum pressure will not be as high because the volume in the cylinders started to increase before the mixture was fully burned.

Of course this is the torque that the combustion produces, the torque that you can use to get your car moving is this value minus what is lost in moving engine parts and friction. This is another reason why the torque drops at high revs, friction gets to play a greater role and moving parts takes more force.

This is a simplified view of things that play a role in what the MEP value is, and therefore what torque value you get. All of these things are not linear processes, this is why a torque curve is not linear at all. In fact it's a very complex curve, it's not even parabolic.

I hope this helped understand why a toque curve can look weird sometime, and why tuning an engine is not a simple task.

PhM
 
If using HP and foot-pounds then:
HP = Torque * RPM / 5,252 and
Torque = HP * 5,252 / RPM

Torque is measured on a dynamometer across a range of engine speeds, the horsepower curve is then derived from these measurements.

There are many good websites that explain all this in detail try googling torque power relationship.
 
I double that!

I wonder how deep this is going to get, technically I mean.
As deep as it can hopefully, while I can't always take part in these discussion I enjoy reading them because it increases my understanding of how it all works.
 
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