Power vs Torque

basis · Mar 16, 2012

Hello guys,

This is not a thread related to and problem. Just to update the knowledge of new car lovers like me!

The question is : What is important to see the power of a engine :

XX PS @ YYYY rpm

OR Torque XX NM @YYYY RPM

what does Torque XX NM @YYYY RPM mean really?

Which one and why important at the time of selecting a car?

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Is the following statement true?
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basis · Mar 17, 2012

Re: PS vs Torque

37 view and no reply?

alanjg · Mar 17, 2012

Re: PS vs Torque

no reply coz its very long stuff to explain..and at this time people are exhausted. Wait tomorrow for response. :P

ilango[speed thirst] · Mar 17, 2012

Re: PS vs Torque

Of course torque is the thing that attacts me , but ps also matter . Eventually when there is a good torque you get good amount of power ,

A peak torque at 2k rpm is better and more efficient.

It also helps you to keep in power band most of the times.

jayadev · Mar 17, 2012

Re: PS vs Torque

basis said:

Basis ,your query is bit tricky to answer . if it was just about technical matters it could be one liner answer .ie . both are interelated if there is a smoke there had to be fire and vice versa.

for the statement you have asked there is nothing hard and set rules in real life.else all the car and automotive races could be prejudged, as this car has this much power so we award it the winner. no it does not happens.

Imagine a two hammer one is 1 kg weight and the other is 10 kg weight .
1.lift 1 kg hammer to 1 meter high and tap on a surface or nail.
2.lift 10 kg hammer to 10 cm (0.1meter) high and tap it similarly on same surface or nail.

(Theoretically) you will see both hammers will give similar impacts or results for the job done, due to distance and acceleration factors; independent of size and mass of hammer.

here the bigger heavier hammer can be regarded as high torque engine .it moves less but has advantage of mass (inertia)

and smaller lighter one have higher rpm. it moves fast and longer gaining much momentum .

The work done on surface if you measured can be indicated in joules,watts or horse power they are nothing but units.

In this case if you change the distance or way you strike it , will affect the impact on surface or on the nail. slower you tap lighter will be the impact .

consider the height of hammer as RPM.then only difference "revolution per minute" in this case is not radius type but like straight line .

depending on the height and speed of the hammer you create needed impact or get your job done.

engine block, mass of cylinder or flywheel and everything else is fixed. only thing you can vary here is revolutions so does you define the ps ,hp and rpm accordingly relatively.

I go with the engine kilowatts. it is not seen commonly in Indian specs but that gives very accurate measure of what your ride is capable of.

say my Punto 90 hp has approx 66 kw engine.

Hope my above trial has somewhat answered your question briefly and quickly.

Please be little more specific about your question .will try to sort if you want .

ilango[speed thirst] · Mar 18, 2012

Re: PS vs Torque

jayadev said:

Absolutely damn best answer one could get .

[thumbsup]

drifter · Mar 18, 2012

Re: PS vs Torque

Torque and power are in a direct relation.

Torque is the rotational force and power is the work done. Or in other words the force done over time. This is where the rpm comes in.

It is good to know where the peak torque is in terms of rpm (and the peak power to a certain extend too. although I do not give too much for it). However, what I am more interested is how wide the torque spreads within 80% of the peak torque range.

The wider it spreads, the better the acceleration and the nicer the car to drive.

Even knowing this does not give away too much about the performance of the car.

What matters is the torque on the wheels per ton over the widest possible rpm range. The lower the torque comes in, the better the fuel consumption and the acceleration. The longer the torque is held, the better is the acceleration.

This goes for 2 cars that are identical other than the engine. If you have the same weight and the same engine, but drive one through a live axle and the other simply transverse, the latter one will be on top as the losses are less.

Obviously, if you have 2 identical cars, which both would accelerate the same because of being identical, it would be different when one car gets the weight removed. The lighter car would not only accelerate quicker but also safe fuel.

Performance on 2 identical cars other than gear box ratio would be different too. The shorter geared one will be quicker and hold it longer on inclines, but would loose fuel economy.

When the cars in question have different tire widths then the one with the thinner ones, will have a higher top speed, quicker acceleration and better fuel economy. Only downside might be that when going to small wheel spin will set in.

If again the cars are identical other than tyre circumference and the the gearing is adjusted to even out the difference (to run at the same gear the same speed at the same rpm), the car with the smaller tyres will be quicker accelerating and use less fuel. This is because of the lesser rotational mass of the tyres.

Other factors like aerodynamics, tyre compounds etc of course have their impact too.

Jerwin · Mar 18, 2012

Re: PS vs Torque

@jayadev , Brilliant answer! [clap]

Thank you very much for that! [cheers]

jayadev · Mar 18, 2012

Re: PS vs Torque

@ Drifter , I believe this is where knowledge of engine power comes handy. say 100kw engine how much it can impart torque and hp to the wheels can be easily calculated.
and the bhp considering all the weight and consumption.

the manufactures generally hide the engine power sheepishly IMO, and shows more BHP with lesser kerb weights and customized gear ratios.but the drawback of such analogy is car would be scorcher with highest FE with a single passenger but when loaded , it would be pain to drive and fuel efficiency goes down the drain.

Tornado · Mar 18, 2012

Re: PS vs Torque

One day , I was driving my diesel car alone, in the night, road was empty & straight.
I incresed the speed up to 120 kmph in 5th gear@2500 rpm, then I took off my foot off the pedal.
The car travelled on its own , for a distance of 1200 m. I felt that was the torque. Similarly petrol td car travels only 300 m.

While the power (bhp) has more to do with the amount of load (weight inside the car).
i.e. if less powered(less ps/bhp) car is loaded up with more number of passeger s , if it has high low end torque then pick up won't be a problem. But being less powered, it will lead to less FE, due to overwork required.
If the car has low low end torque then pick up will be reduced , even if bhp/ps is more.

So my understanding is that , torque vs ps, is a wrong comparison. Both complement each other in fact.

Higher torque + higher ps = better pick up + better load carry capacity ,so better FE i.e. better performence like crdi cars

Lower torque + higher ps = poor pickup but better load carry capacity. but little poor F E like trucks, non crdi diesel cars

Petrol cars come with lower torque but higher bhp , their pickup is better but at the cost of FE.

jayadev · Mar 18, 2012

Re: PS vs Torque

That should be due to momentum or out of inertia of the mass.

Torque is rotational force say when you tighten a nut or bolt ,you have to apply a force on the wrench or spanner.
here The magnitude of torque depends on three quantities: the force applied, the length of the spanner connected to the nut the point of force application i.e from where we push or pull the spanner.

I a rotary motor/ engine it is rotational hence it comes in radians.(it becomes bit complex so let us leave it)

Power / 2 X pi X rotational speed = torque

BHP:- is final power available for commute for our use, ie. power(horse power) available after the friction in gear box,alternator,body wieght,airconditioner ,tire losses etc.

Though it is not complementary but interrelated or directly proportional.

E.g. the torqe come when fuel explodes in the cylinders. and that explosion pushes the cranks and gears turning into revolutions.

If too much high torqe is required at high rpms ,lot of fuel needs to be burned (very well explained by Drifter in earlier posts). cylinder needs to be pushed continue sly and tremendously.

Generally at high rpms manufacturer reduce the fuel supply considerably to increase FE the higher rpm takes benefit of momentum of the flywheels to an extend.

Considering all these aspects does a modifier does job pleasing the owner.

As drifter has already mentioned..I am just adding my cents

it is not only the rpm but the mass to power ratio or bhp/ton ratio. even diesal cars can be made to sprint.
Hyundai verna 1.6 diesal does 0-100 in 10+ secs, Linea 1.4 petrol does 0-100 in 13+ secs.

it all depends upon ger ratios, bhp/ton ratio,over all engine quality too.

basis · Mar 19, 2012

Re: PS vs Torque

Hello jayadev,

Thanks a lot for all your inputs, It's helps me..really.

Thx again.

Now comming to the point, for a petrol car selection :

I have attached a config. within Car A-B-C-D

Can you pl. check the attachment and let me know how these all foiur are diffrent! Which is OPTIMUM/safest (might be not the best!) in terms of pulling power/pickup/takeover/highway/Ghat/city drive?

Thanks in advance.

drifter · Mar 19, 2012

Re: PS vs Torque

basis said:

If you had read my last post then you wouldn't have have bothered bringing up the attachment.

Many of the important details are missing.

jayadev · Mar 19, 2012

Re: PS vs Torque

basis said:

Those figure only give a narrow view of picture you want to see.like you take 2 glass of water from different river and ask which is faster,deeper,wider river.

either the figures of power delivery at wider range or the graph of power delivery will give a sure shot conclusion .

there would be peaks and dips in graph . generally manufacturer provides the peak power figure if the same is too narrow then whole thing is senseless.

the car which gives maximum torque at the rpm at you prefer to drive would be obviously beneficial in general and we dont generally rev to 6000 or 7000 rpm.

I would prefer1197cc, 80 @5200,t:112@4000. it seems to have more linear power delivery at lesser rpms. means good midband power .nice for overtaking,ghats.

1197cc 68@6000,96@2500 is good for city rides.good pickup at low revs and good pulling power.
if it is a small car of 600kg weight it can be considered a quick sports car !!

basis · Mar 19, 2012

Hello jaydev,

Thanks for a more clear picture.

Let's now open the names :

From L to R ->

A : Ford Figo Duratec Petrol Titanium 1.2

B: Fiat Grande Punto 2012 Dynamic 1.2

C: Hyundai i20 Magna 1.2 (New upcomming VVT petrol motor will be better)

D: Maruti Suzuki Swift DZire VXI

This one is Punto 1.2 ! The heaviest of all four!

This one is Hyundai i20 Magna 1.2!

So for a layman in car issues, just the final word....

do you think this Hyundai i20 Magna 1.2 is the overall wiener here in all aspect? (I mean not best in might in any segment for over all suitable for good pickup/pulling / city /highway/ghat drive?

Power vs Torque

basis

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basis

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alanjg

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ilango[speed thirst]

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jayadev

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ilango[speed thirst]

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drifter

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Jerwin

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jayadev

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Tornado

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jayadev

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basis

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Attachments

drifter

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jayadev

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basis

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