Torque vs. Horsepower: The True Answer Explained

[Insider]

Originally Posted by needforspeed

Right ....

Teknochild ... you are saying that torque is applied 'more often' at higher rpms than at lower rpms ... which multiplies its effect ... such that peak acceleration occurs at the horsepower peak.

You have based this on the assumption that the banks of cylinders in an engine fire in turn so that torque is applied intermittantly.

However, in an engine the cylinders are timed to fire in turn. In combination they push the pistons against the crankshaft to induce a CONSTANT rotational force:

http://en.wikipedia.org/wiki/Crankshaft

Now consider the analogy of a lightswitch. If you turn it on and off at regular intervals 1000 times a minute it will be 'on' for half a minute. If you do the same thing 7000 times a minute it will still be 'on' for half a minute. It doesn't matter how many times you cycle the lightswitch the light will still be on for the same amount of time.

So thinking about an engine - logically torque CANNOT be delivered 'more' at 7000rpm than at 1000rpm. In each case the torque would be applied for exactly the same amount of time and the application of the torque would be smoothed by the pistons and the crankshaft.

Finally, torque is a measured value. The torque measured at 7000 rpm is just that .... we don't measure 500nm and then multiply it (or divide) it because of the rpm ... so if an engine is rated to produce 500nm at 7000rpm then that is what it produces - no more no less.

If the rpm is held constant then the torque will be held constant - it is neither intermittant or cumulative. This torque will be partly used to offset the forces of road and wind resistance to enable a vehicle to travel at a constant velocity and, if there is enough, it will also accelerate the vehicle.

The level of acceleration will be dependant on the level of torque applied. Not the engines rpm.

This is proven when you consider the response in different gears. In lower gears the torque is multiplied by the gear ratio. Vehicles accelerate more rapidly in these gears as a result simply because more torque is generated at the wheels. The revs are the same in each gear, but the gear multiplies the torque ... so it's the torque that causes the acceleration.

If in any doubt consider that the 330i gets to 60mph from a standstill much faster than it gets from 60mph to 100mph. The most rapid acceleration is in the lower gears where the wheel torque is highest.

Every explanation of HP and torque I can find on the internet agrees that acceleration peaks when wheel torque peaks. As I have said before I can't find anything which backs up your view and I cannot see how it can logically be correct.

Makes sense to me. Max acceleration occurs at peak torque, not HP. You can also feel this when driving in the real world.

[NFS]

Originally Posted by Insider

Makes sense to me. Max acceleration occurs at peak torque, not HP. You can also feel this when driving in the real world.

To further demonstrate this I have looked at the acceleration times in 10mph increments for the 330i from here:

http://drive-channel.blogspot.com/20...i-vs-2007.html

I've done the following little calculation

Time Speed Time Per 1mph increase

0 0
2 30 0.07
3.4 40 0.14
4.7 50 0.13
6.2 60 0.15
8.5 70 0.23
10.6 80 0.21
13.5 90 0.29
16.8 100 0.33



What this shows is that at lower speeds (and hence lower gears) the vehicle is gathering speed most quickly. Between 0 and 30 mph the car is gaining an average of 1mph per every 0.07 seconds, but it takes 0.33 secs to gain every 1mph between 90 and 100mph.

This demonstrates that the acceleration is greatest in the 1st gear. The reason is that wheel torque is greatest in 1st gear.

[teknochild]

your so wrong in so many places its not even funny

first of all as i already said we are taking gearing OUT of consideration, but since you absolutly HAVE to bring it in you need to realize something GEARING CHANGE HORSEPOWER TOO, saying that "This demonstrates that the acceleration is greatest in the 1st gear. The reason is that wheel torque is greatest in 1st gear" is idiotic because horse power increases and decrease in proportion to torque in every gear

next if you take a look at that graph you posted or the graph in the force induction section or 90% of the graphs for speed + time out there you will notice something EACH GEAR HAS AN ALMOST COMPLETLY CONSTANT SLOPE which meens each gears acceleration appears to be the same through each gear

now thats obviously not true because both HP and torque are fluctutating, but if you had a brain and realized that the data you are using is one: not sampled at a fast enough rate (i meen seriously are u a fing idiot its sampled every 10mph you would get an F in physics if you did something that stupid) and two: it is not precise enough to yield any results (it needs to be precise to at least tenths of a mph if not greater and sampled at rates of at least every .5 seconds)

so good job on TRYING to bring some science in, but please do it properly next time

also you totally forgot that that is a real life example and that air resistance and friction have now been thrown into the mix, good job


now i want you to tell me why you think, that torque output is constant, you linked a wikpedia article of a crankshaft but NOWWHERE in their does it say torque is output constant, infact if anything it says otherwise

torque from an internal combustian engine will never be constant, even if its timed perfectly to put out a constant minimum amount of torque (which they are) they will always have larger peaks of torque, even electrical engines dont put out constant torque, but the variances are so small i doubt you could measure them



now tell me something, if you know that force is applied yields acceleration, and that cylinders put out similar torque in their effeciency range, tell me HOW you come to the conclusion that a cylinder firing twice will apply the same net force as a cylinder firing once PLEASE i want to know how your head has come to this

[teknochild]

you have basically started arguing about something totally diffrent, your trying to tell me that the lower the gear the more acceleration vs a higher gear because torque is higher in the lower gears, even though horsepower is also higher in lower gears

you have not come up with a SINGLE thing to support your idea that torque alone means greater acceleration except for how you feel, even the above that is the closest you have come to bringing a scientific explanation does to show anything, not only because its invalid as an experiment but because IT DOES NOT SHOW ANYTHING, compating the acceleration of 5th gear and first gear CANNOT SHOW ANY DISTINCTION BETWEEN TORQUE OR HORSEPOWERS EFFECT ON ACCELERATION

if you wanted to go that route you should have gotten the acceleration results FROM ONE SINGLE GEAR sample at a rate of AT LEAST every half second with a precision of AT LEAST tenths of a mile per hour

[NFS]

Originally Posted by teknochild

you have not come up with a SINGLE thing to support your idea that torque alone means greater acceleration except for how you feel, even the above that is the closest you have come to bringing a scientific explanation does to show anything, not only because its invalid as an experiment but because IT DOES NOT SHOW ANYTHING, compating the acceleration of 5th gear and first gear CANNOT SHOW ANY DISTINCTION BETWEEN TORQUE OR HORSEPOWERS EFFECT ON ACCELERATION

You continue to be rude and ignorant which I don't appreciate even slightly.

You can't bully people into agreeing with you.

EVERY article on this subject supports my statement that acceleration peaks when wheel torque peaks.

Thats EVERY single one.

I have demonstrated why your argument is flawed. You have not been able to respond to that argument.

I challenge you to post one piece of independant information that says that acceleration peaks at peak hp.

For every one item that you can find to prove this I will find 5 that say it peaks at peak torque.

You keep talking about science - please understand the reason I do not believe you is:

1. You have not explained in any sensible logical way why your synopsis is correct.

2. All of the literature on the subject says that I am right

3. You cannot come up with any independant evidence that you are correct

Now ... I'm still man enough to believe that I could be wrong ... so come on .. prove you are right .. find something which backs up your statement

Oh and BTW the graph I posted was something I knocked up at work. What I wanted to demonstrate was simple .. that acceleration in lower gears was greater than in higher gears.

By behaving in this insulting manner you simply demean yourself.

[NFS]

Originally Posted by teknochild

now thats obviously not true because both HP and torque are fluctutating, but if you had a brain and realized that the data you are using is one: not sampled at a fast enough rate (i meen seriously are u a fing idiot its sampled every 10mph you would get an F in physics if you did something that stupid) and two: it is not precise enough to yield any results (it needs to be precise to at least tenths of a mph if not greater and sampled at rates of at least every .5 seconds)

Not the case ... absolutely not.

Torque is a measured value. If an engine is revved at a steady rpm it will produce a steady torque. If there WERE minor fluctuations then they would be flattened out by the measurement process. Otherwise ... one could simply not effectively measure torque.

Now ... In my post I explained why the torque if it were intermittant would be applied no more or less often at 7000 rpm than at 1000 rpm.

If you are so damn sure of yourself explain why that is incorrect. Don't just say 'that's wrong' without any attempt to explain why.

In my experience people often behave in a belligerant and aggressive way when they know themselves to me in the wrong or they do not understand something entirely and don't want to admit it.

If you understand this then prove it ... explain it and explain why I am wrong.

[teknochild]

Originally Posted by needforspeed

Now ... In my post I explained why the torque if it were intermittant would be applied no more or less often at 7000 rpm than at 1000 rpm.

If you are so damn sure of yourself explain why that is incorrect. Don't just say 'that's wrong' without any attempt to explain why.

i showed you PROOF that torque is not applied constantly, the dynamics of a combustian engine do not ALLOW torque to constant even at steady RPMs

if the effeciency is the same @ 7k as 1k no more torque is applied at a time, but more NET FORCE is output by the engine, this is FACT

and i DID explain to you, i even showed you a diagram, torque is constantly varying during a combustian stroke, add more cylinders for overlaping and it varries LESS but it STILL VARIES

a 4 cylinder engine only has 1 chamber combusting at a time, while the other three are on their exaust fuel and compression strokes, how are you going to sit there and tell me that engine outputs constant torque, i showed you PROOF that a combustian stroke outputs varied torque


do you need me to go back and copy and paste what i have showed you already three times? is that really neccisary?

Originally Posted by needforspeed

Torque is a measured value. If an engine is revved at a steady rpm it will produce a steady torque. If there WERE minor fluctuations then they would be flattened out by the measurement process. Otherwise ... one could simply not effectively measure torque.

and yea thats exactly right, the fluctuations ARE flattened out by the process, as i already stated if the sample rate was increased to a high enough rate you would be able to measure the fluctuations




its a simple fact that an engine that outputs an avg of 50 torque a cylinder is going to output more net force after two combustians then one

[NFS]

Originally Posted by teknochild

i showed you PROOF that torque is not applied constantly, the dynamics of a combustian engine do not ALLOW torque to constant even at steady RPMs

if the effeciency is the same @ 7k as 1k no more torque is applied at a time, but more NET FORCE is output by the engine, this is FACT

and i DID explain to you, i even showed you a diagram, torque is constantly varying during a combustian stroke, add more cylinders for overlaping and it varries LESS but it STILL VARIES

a 4 cylinder engine only has 1 chamber combusting at a time, while the other three are on their exaust fuel and compression strokes, how are you going to sit there and tell me that engine outputs constant torque, i showed you PROOF that a combustian stroke outputs varied torque


do you need me to go back and copy and paste what i have showed you already three times? is that really neccisary?





and yea thats exactly right, the fluctuations ARE flattened out by the process, as i already stated if the sample rate was increased to a high enough rate you would be able to measure the fluctuations




its a simple fact that an engine that outputs an avg of 50 torque a cylinder is going to output more net force after two combustians then one

The link you posted just showed a combustion cycle and indicated that the torque varied during that combustion cycle.

As I said ... and you seem to agree ... engine timing and crankshaft design is such any rapid fluctuation in torque during the combustion cycle would be smoothed.

As the gases in the cylinder explode the piston is pushed out turning the crankshaft, that creates torque, the torque generated by the next combustion in the next cylinder drives the crankshaft further round and in so doing it returns the 1st piston back to it's original postion. The rotational forces on the crankshaft then would seem to be pretty much constant.

As I also said ... if you cycle something on and off 1000 times per minute or 7000 times per minute it is still on for half of the time. The frequency of the cycle is irrelevant.

This makes me doubt the logic of your position.

The fact that torque is a MEASURED value makes me doubt it even more.

IF torque fluctuates (and it is a big IF) then any torque measurement would need to account for this ... if it didn't it would be utterly irrelevant.

The other reason I doubt what you say is that NO-ONE else says it.

EVERYTHING I have read said max acceleration is at the transmission output torque peak.

For example:

http://www.allpar.com/eek/hp-vs-torque.html

(this one is very interesting - he is saying shift to maximise power - which means the same as maximising the transmission torque peak !!!!)

http://g-speed.com/pbh/torque-and-hp.html

(Maximum acceleration in any gear occurs at the torque peak!!)

http://www.houseofthud.com/cartech/t...horsepower.htm

(maximum acceleration of you car is made possible by maximising your output torque!!!)

http://www.v8914.com/Horsepower-v-torque.htm

(I posted this one before - What we are really interest in is the average torque at the wheels through out the complete run!!!)

http://www.ar1.ws/DaveC/Horsepower.htm

(Maximum acceleration in any gear occurs at the torque peak!!)

http://www.flamesonmytank.co.za/Articles/torque.htm

(You will need maximum torque for fast acceleration!!)

http://vettenet.org/torquehp.html

(a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it!!)

http://www.calsci.com/motorcycleinfo/Horsepower.html

(More torque equals more push, which equals more acceleration, which wins races!!!)

I think that's 8 articles that say I am right ... can you find even one other person who agrees with what you are saying ??

Do you think all these other people are idiots too ?? Is anyone who disagrees with you an idiot ??

If all these people (including myself) are wrong why are they wrong ??

[NFS]

Originally Posted by teknochild

its a simple fact that an engine that outputs an avg of 50 torque a cylinder is going to output more net force after two combustians then one

No it isn't ... it is not a fact at all.

Torque is force times distance ... it does not include time ... you can't add 2 lots of torque together at different times and talk about 'more net force'.

There IS a measure which factors in force, distance and time ... it's called horsepower.

[teknochild]

Originally Posted by needforspeed

The link you posted just showed a combustion cycle and indicated that the torque varied during that combustion cycle.

As I said ... and you seem to agree ... engine timing and crankshaft design is such any rapid fluctuation in torque during the combustion cycle would be smoothed.

As the gases in the cylinder explode the piston is pushed out turning the crankshaft, that creates torque, the torque generated by the next combustion in the next cylinder drives the crankshaft further round and in so doing it returns the 1st piston back to it's original postion. The rotational forces on the crankshaft then would seem to be pretty much constant.

As I also said ... if you cycle something on and off 1000 times per minute or 7000 times per minute it is still on for half of the time. The frequency of the cycle is irrelevant.

This makes me doubt the logic of your position.

The fact that torque is a MEASURED value makes me doubt it even more.

IF torque fluctuates (and it is a big IF) then any torque measurement would need to account for this ... if it didn't it would be utterly irrelevant.

The other reason I doubt what you say is that NO-ONE else says it.

EVERYTHING I have read said max acceleration is at the transmission output torque peak.

For example:

http://www.allpar.com/eek/hp-vs-torque.html

(this one is very interesting - he is saying shift to maximise power - which means the same as maximising the transmission torque peak !!!!)

http://g-speed.com/pbh/torque-and-hp.html

(Maximum acceleration in any gear occurs at the torque peak!!)

http://www.houseofthud.com/cartech/t...horsepower.htm

(maximum acceleration of you car is made possible by maximising your output torque!!!)

http://www.v8914.com/Horsepower-v-torque.htm

(I posted this one before - What we are really interest in is the average torque at the wheels through out the complete run!!!)

http://www.ar1.ws/DaveC/Horsepower.htm

(Maximum acceleration in any gear occurs at the torque peak!!)

http://www.flamesonmytank.co.za/Articles/torque.htm

(You will need maximum torque for fast acceleration!!)

http://vettenet.org/torquehp.html

(a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it!!)

http://www.calsci.com/motorcycleinfo/Horsepower.html

(More torque equals more push, which equals more acceleration, which wins races!!!)

I think that's 8 articles that say I am right ... can you find even one other person who agrees with what you are saying ??

Do you think all these other people are idiots too ?? Is anyone who disagrees with you an idiot ??

If all these people (including myself) are wrong why are they wrong ??

actually your right, unfortunatly, and ill admit it, but only because we have gone totally off track of what the original argument was, which was that more horsepower gets you there faster regardless of torque by itself, and in the end will yield a higher average acceleration


but your still wrong that engines output constant torque, that part i was right about, just not that it compounds at faster rpms

[NFS]

Originally Posted by teknochild

actually your right, unfortunatly, and ill admit it, but only because we have gone totally off track of what the original argument was, which was that more horsepower gets you there faster regardless of torque by itself, and in the end will yield a higher average acceleration

but your still wrong that engines output constant torque, that part i was right about, just not that it compounds at faster rpms

Thank you ... is it too much to ask that you might retract some of your insults

As it happens I think you are correct that torque will fluctuate ... I just don't think it is relevant to the torque figures we see posted for given engine speeds. We would be talking about incredibly rapid fluctuation and any measured value would need to average this out. I also think that the way the crankshaft and timing system works will turn a sporadic rotational force into an (almost) constant one.

I came into this discussion a little late with post 93 on this page:

http://www.e90post.com/forums/showth...t=40423&page=5

What I said in that post still stands and for other peoples benefit it is worth repeating:

1. You accelerate fastest when wheel torque is highest.

2. Wheel torque can be calculated for any given rpm in any given gear quite easily. Doing this demonstrates why it is not sensible to shift at an engines torque peak ... the reason is gearing. Because of the way in which gearing amplifies torque it is USUALLY better to stay in a lower gear for as long as possible. However this is not always the case (indeed it is worth short shifting in the BMW 530d).

3. Because of the amplification of output torque that can be achieved through gearing it is MUCH beter to have high torque at high rpms. If you can gear the rpms down by a factor of 3 then torque increases by a factor of 3 !!!

4. High Torque at High RPMS means high horsepower. That is why horsepower is good ... higher horsepower engines can generate more wheel torque for longer because of gearing.

The only point we have disagreed on is that maximum acceleration is when wheel torque is at a maximum. I do agree that high HP = a quick car. But you have to think about torque curves and gearing as well.

This is compounded by modern diesels ... the 530d (my old car) has stupendous torque (as much as a 550i) but relatively low HP in comparison. The reason the HP is low though is that the engine doesn't rev high. Fortunately - the torque spread is very wide - and it is very cleverly geared (6 forward gears) this means that wheel torque is consistently very high ... so it's a quick car.

It's been an interesting debate and I really had to think about WHY I disagreed with you and why my position was right.

Next time it would be more fun if you didn't call me an idiot quite so often

[NFS]

BTW I think you also owe top gear an apology ...

He answered your multiple choice correctly (as I did) and your response was ..

"jesus you are dumb"

Clearly top gear wasn't - in fact he was absolutely right !

[Norsk]

This is great stuff ;-)

Thanks to Daniel, TopGear & Josh

Ahhhh, I miss my Physics classes & experiments

[NFS]

Originally Posted by Top_Gear

There is a lot of physics mumbo jumbo in these links that take the reader off topic. However, one of the referenced articles shows an excellent example comparing two different cars with identical peak horsepower. Take a read of the bottom half of the article in this link titled "A Complex Example"

http://craig.backfire.ca/pages/autos/horsepower

The example is really not that complex but requires a bit of patience when reading it. It describes two different cars called "ricer" and "redneck". The "rednceck" car has big torque but small rpm range (small redline) and the "ricer" car has small torque but huge rpm range (huge redline). The author goes on to show how the selection of proper gearing can make the performance of these two cars nearly identical.

It's a great read. If you can unserstand this one example you pretty much have understood the concepts of torque-power-gearing.

I missed the article in Top Gears post earlier.

Having just read it through I would say it is the clearest and most informative article on the subject I have seen.