Power vs Torque


Thread Starter #1
Joined
Mar 5, 2011
Messages
383
Likes
3
Location
Bangalore
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?


===============================================
Is the following statement true?
======================

People are impressed by giving paper figures.Honda Jazz Power 90 PS @6200 RPM Torque 110 NM @4800 RPM on such high RPM ?Punto 1.2 Power 68 PS @6000 RPM Torque 96 NM @2500 RPM. on such low RPM Wow !Power is only reving capacity of engine. Torque means rotational force of engine to drive the car.So torque figure is important while choosing car.honda gives full torque @4800 RPMBut if you go for punto then max. totque of Punto is only @2500 RPM such a low RPM.In Punto you have to press less throttle for getting full potential from powerband. Less gear changes & better low end totque. Honda feels gutless city ride as well as highways .Because max torque of Honda is @4800 RPM. In real world we can' accelerate car upto 4800 RPM in any gear for getting full potential outpur from its engine.So cars giving max torque @ lower RPM is always wise choice. So friend dont'be impressed by seeing power figure of H Jazz.Because if you go for JAZZ , in Ghat section (hilly area) Punto 1.2 will easily beat HOnda Jazz. Then you will feel disappointed by seeing low powered car is "King of Ghat"
 
Joined
Jan 16, 2012
Messages
10
Likes
1
Location
Bangalore
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
 
Joined
Sep 12, 2009
Messages
4,052
Likes
278
Location
Pondicherry
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.
 
Joined
Nov 1, 2010
Messages
4,237
Likes
372
Location
Kannur,Kerala
Re: PS vs Torque

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?
===============================================
Is the following statement true?
======================
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 .
 
Last edited:
Joined
Jul 20, 2011
Messages
200
Likes
12
Location
London/Mumbai
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.
 
Joined
Nov 1, 2010
Messages
4,237
Likes
372
Location
Kannur,Kerala
Re: PS vs Torque

Even knowing this does not give away too much about the performance of the ca
@ 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.
 
Last edited:
Joined
Feb 3, 2012
Messages
3,317
Likes
2,020
Location
Deccan Platue
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.
 
Joined
Nov 1, 2010
Messages
4,237
Likes
372
Location
Kannur,Kerala
Re: PS vs Torque

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.
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


While the power (bhp) has more to do with the amount of load (weight inside the car).
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.

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


Petrol cars come with lower torque but higher bhp , their pickup is better but at the cost of FE.
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.
 
Thread Starter #12
Joined
Mar 5, 2011
Messages
383
Likes
3
Location
Bangalore
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.
 

Attachments

Joined
Jul 20, 2011
Messages
200
Likes
12
Location
London/Mumbai
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.
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.
 
Joined
Nov 1, 2010
Messages
4,237
Likes
372
Location
Kannur,Kerala
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.
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 !!
 
Thread Starter #15
Joined
Mar 5, 2011
Messages
383
Likes
3
Location
Bangalore
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


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


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.
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?

 
Top Bottom