Talk:Power band

Article is technically flawed

I regret to say that the definition of "Power band" given, and thus the core of the entire article, is arbitrary, unreferenced (and indeed I have never heard this definition outside of wikipedia), and demonstrably false/misleading. The idea that the power peak represents the end of the useful power band is, for all real cases that are not limited by redline while power is still rising, completely false, as for maximised power output with fixed gear ratios one should only move to the next gear once power in the current gear drops below power at the RPM that one would drop to in the next gear - which never happens immediately after power peak except with a power curve gradient after power peak of negative infinity (read: impossible). So optimum ratio and shift point design would demonstrably ALWAYS be superior if it does NOT stay in the power band given here.

The idea of the torque peak being the lower limit is similarly arbitrary and meaningless. One could easily imagine a motor where operating at the torque peak gives extremely poor acceleration compared to operating near the power peak - all it would require is a relatively long, flat torque curve.

This article, in my opinion, needs to be reworded or rewritten with the knowledge in mind that there is no measurable, global definition of power band, as it depends entirely on the usage case of the motor. And the false metric given needs to be removed before someone who has read this article actually tries to use it when making a critical decision. Having said that, I will wait for someone else to agree with me as I don't have time to rewrite the article and don't feel it would be appropriate to butcher the whole thing, which is what would be necessary to remove inaccuracies without a rewrite. --Nereth (talk) 01:57, 9 April 2014 (UTC)

I agree, my own knowledge tells me this article is either misleading or wrong in several areas, but i don't feel I have enough knowledge to correct it. — Preceding unsigned comment added by Gav Newman (talk • contribs) 09:43, 5 February 2016 (UTC)

All right, I tried to correct some of that (and ended up rewording and rearranging many other parts of the article). The definition in the lede still doesn't mention that the definition varies between use cases, but I think it's better now than it was before. As long as "around peak power" isn't too vague for an encyclopedia, anyway. ;) 87.108.17.117 (talk) 18:15, 5 July 2017 (UTC)

Power and torque

This article seems to gloss over the fact that power is not independent of torque. It is in fact just torque multiplied by angular velocity (which is directly derived from RPM). There is no such thing as power without torque. An engine with constant torque over an RPM band will demonstrate a peak at the high end of that band. A given torque at 2000 RPM represents twice as much power as the same torque at 1000 RPM. At 3000 RPM, it's three times as much power and so on. In linear kinetics, it is power = force x speed. In rotational kinetics, it's power = torque x angular velocity.

So even this "torquey" engine has to be used at a high RPM to extract the most power out of it.

The "peaky" engine typically has poor low-end torque, so the power drop with decreasing RPM is worse than linear.

Honda's F20C does not have "little torque". It has lots, just not in the lower RPM range. No wonder: the variable valve timing (VTEC) does not kick in until 6000 RPM.

I don't see a problem with the article as it is. It may gloss over the relationship between power and torque, as that is not the subject of the article, but it's certainly not incorrect. The F20C produces 153 lb-ft of torque. That's not much. The engine's advantage is its ability to operate at ridiculously high speeds, which allows it to produce good power in spite of a relative lack of torque. Of course a "torquey" engine will produce more power at high RPMs, but the point is that it produces enough torque to be usable over a wide RPM range. I welcome you to work to improve the article as you've improved close-ratio transmission, but please be careful to keep it readable and easy to understand for a wide audience. Too much detail can be as bad as too little. TomTheHand 15:51, 23 February 2006 (UTC)

Actually the F20c is a very efficient at producing torque, producing 76.5 lb-ft per liter. The "torquey" Dodge Viper produces only 64.5 lb-ft per liter and the Corvette Z06 only produces 67 lb-ft per liter. Also both of those engines have very narrow torque bands, falling off steeply before and after the peak. If I remember right the F20C produces a very flat torque curve like many Honda engines that use VTEC. So really the F20C is not a "peaky" engine, it just needs to kept at high revs to extract its power. IJB TA 04:58, 5 October 2006 (UTC)

So I guess the only problem I can see with this article is that it seems to state that producing a larger amount of torque will somehow lead to better vehicle performance in "Tuning for high Horsepower Output or high Torque Output?" IJB TA 05:17, 5 October 2006 (UTC)

I changed the "Tuning for high Horsepower Output or high Torque Output?" section, the comparison of the Honda S2000 to the VW Touareg made absolutely no sense. IJB TA 06:37, 12 October 2006 (UTC)

Diagrams

A couple of diagrams would be the bees knees. It can be difficult to visualize these sorts of things, especially if one has never seen a power curve. A diagram illustrating a power band would be the first priority, of course, but a side-by-side of a peaky and torquey engines would really round things out (I think a side-by-side would be better than an overlay, lest people confuse the two lines for power & torque from one engine). This article is, IMO, very well written, and diagrams would be the icing on the cake. ENeville 16:29, 13 September 2006 (UTC)

I agree. I used to have a program that would estimate power and torque curves from parameters you'd put in, and you could take an engine, "swap in" an aggressive camshaft, and see how low-RPM torque would suffer but torque would be maintained, and horsepower would continue to climb, to higher RPMs than before. I don't have the program available any more, but I would love to see something like that here: power and torque curves of two engines identical except for cams, one "torquey" and the other "peaky." TomTheHand 18:16, 13 September 2006 (UTC)

I put something together in Excel but it's kind of artificial. I'll upload it and see what you guys think. TomTheHand 18:44, 13 September 2006 (UTC)

I added the diagram, but I need to revise it through a few successive versions. If anyone has access to more hard information (an actual dyno sheet showing pulls before and after a cam swap would be great!) please replace it. If there are suggestions about what I should do to it, please tell me and I'll get them done! TomTheHand 18:57, 13 September 2006 (UTC)

Points for improvement

Some things this article still needs:

1. REFERENCES. This is high priority. Without it, the article just reads like it could be one person's essay on power band tuning, and more importantly it violates WP:V and WP:NOR.
2. An explanation of the power=torque X angular speed equation would be very useful and illustrative to the reader. This should be coupled with the diagram(s) of dyno pulls and the tuning section.
3. We could probably come up with better sub-headings than those currently used. Using a question in a sub-heading IMHO is bad style.
4. Might this article not be better served by being wholly merged into engine tuning as a section on its own?

My brain's too frazzled to contemplate a major edit and reference hunt, maybe next week I'll tackle these. Any other suggestions? Zunaid 11:21, 5 October 2006 (UTC)

Re (2.), from long experience I say that the horsepower and torque relationship is one where there's a large static wave of interest leading understanding, populated substantially by people quite convinced that they know what's right, even though what they believe is wrong. I think it would be helpful to try to contain the resultant concentration of edits and comments, and evidently steep part of the learning curve, to a single page on that subject.

Re (4.), I think it could be either way. I don't think it's worth moving, though, IMO. ENeville 17:07, 11 October 2006 (UTC)

Wind Turbine power curve

Power curve redirects here. However wind turbines have also a "power curve diagram" (i.e.[1]) that could be described here (or on a different page)--VictorAnyakin (talk) 12:55, 7 December 2008 (UTC)

Milage

Where in the power band do you get best gas milage? Or more precisely, at which rpms do you get highest engine power conversion efficiency (from chemical energy to rotational energy)? — Preceding unsigned comment added by 69.171.160.251 (talk) 12:11, 7 February 2012 (UTC)

Electric motor section is flawed.

Electric motors DO NOT produce a flat torque curve themselves. The flat torque is the result of current limiting done by the electronic controller when a mass is being accelerated and throttle input to the speed controller is asked to give out 100% torque (the "gas pedal" floored down to the max at all times from starting at dead stop to full velocity of the mass), which is limited to the current limit of the motor speed controller since torque is directly proportionally to current. Also, no reference was made to the fact that the Tesla vehicles use a special type of speed controller that is called a Vector control (motor) https://en.wikipedia.org/wiki/Vector_control_(motor), which allows direct control of the torque for AC induction motors by controlling the current that is responsible for the torque since ac induction motors are not quite as easy to control as brushed DC motors when it comes to speed and torque control. — Preceding unsigned comment added by Dennis Reece (talk • contribs) 17:58, 12 January 2015 (UTC)