Whats the difference between Torque and Horsepower

[Denilson]

Rotary Junkie: I agree with all you said, but I need to ask you what you're refering to below?

CSL, you're somewhat wrong with saying that peak torque isn't peak thrust.

If you refere to "Thrust" as "Torque at the wheels", I have to disagree.
Torque at the wheels are exactly the same as effect/rpm's at the wheels.

And if we achieve peak thrust (given that I understand your word "thrust", lol) at peak bhp (i.e 500 bhp) at, say, 6000 engine rpm's, how is it possible that we can also achive peak thrust at the wheels at 3000 engine rpm's (peak engine torque is produced here).

So this engine (i.e):
[(350 / 3000) * 5252] = 612 Lbft (peak torque)
[(500 / 6000) * 5252] = 437 Lbft (peak bhp)

The engine torque is much higher @ 3000 rpm compared to @ 6000 rpm.
But we'll still achieve peak wheel torque (thrust) @ peak bhp.

So what happens with the torque on it's way from the engine to the wheels?
1. We have 437 Lbft / 500 bhp @ 6000 rpm's.
2. Power/torque goes thru the gearbox, and in, say, 2nd gear, the ratio is 1:2.5.
3. We now have 1092 Lbft / 500 bhp at the output shaft.
4. Then, the power and "new" torque reach the diff, which is set to 1:3.
5. We now have 3277 Lbft on the axle.. But still 500 bhp.

Peak thrust = peak bhp (effect)
Peak torque (612 Lbft) is'nt the same as peak thrust.

And again, this is if I understand what you're refering to as "thrust", but given that you quoted CSLACR, who replyed to PAPPACLART's post, I think I'm on the right page here. 👍

 

[Bopop4]

Reminds me.

A friend once remarked: WRC cars may be limited to around 300-400 hp... but nobody's saying over how much of the rev range they hold it.

They have it for most of their rev range, the engines can produce way more power, but they use ignition timing and fuel mixture to create a flat power curve throughout almost all of the rev range.

I would imagine that it would look flat from about 3000-4000RPM all the way to 7000-8000RPM.

EDIT: No, my mistake, that's how GT500 cars do it, WRC cars just have restrictors on the engine to limit airflow and boost pressure, they can have as much power as they want, but it's tuned to give it over a wide range of revs.

 

[alexlam24]

Horsepower is how fast you hit a wall
Torque is how far the wall moves when you hit it

 

[Famine]

So what happens with the torque on it's way from the engine to the wheels?
1. We have 437 Lbft / 500 bhp @ 6000 rpm's.
2. Power/torque goes thru the gearbox, and in, say, 2nd gear, the ratio is 1:2.5.
3. We now have 1092 Lbft / 500 bhp at the output shaft.
4. Then, the power and "new" torque reach the diff, which is set to 1:3.
5. We now have 3277 Lbft on the axle.. But still 500 bhp.

The crankshaft and the gearbox input shaft are subject to the same torque, connected through by the clutch. The gearbox multiplies the torque to the output shaft.

Peak thrust = peak bhp (effect)

Thrust = lbf, kgf, N = Force
Torque = lbfft, kgfm, Nm = Work
Power = lbft/s (hp), kgm/s (PS, CV, Ch), W = Power

 

[Denilson]

The crankshaft and the gearbox input shaft are subject to the same torque, connected through by the clutch. The gearbox multiplies the torque to the output shaft.

Yes. Sorry. My english skills regarding correct terms in technical areas is'nt what it should be from time to time. Thanks for correcting it. 👍

 

[homeforsummer]

But you just (your first sentance in the quote above) said that PAPPACLART is refering to torque at the wheels.. Then you drop your next sentence like a bomb..

PAPPACLART is referring to torque transmitted to the wheels, which is the effort you feel when driving. My comment was that torque at the flywheel is the one manufacturers quote, hence the one the press quotes. I don't see the confusion.

You got to be kidding me?
How fast will this engine be?

If you still think that torque alone would tell you about an egines performance, you better give me an example of one.
I doubt you'll find one though..

Quit with the arbitrary bloody figures with high torque and low RPMs. Any idiot knows that an engine has to be turning at some revs to deliver its power and torque, so saying "oh, but 500 lb ft doesn't do anything at 5rpm" is completely irrelevant.

And at no point have I claimed that torque alone would tell you about an engine's performance. You're clearly proficient enough in English to converse on the subject so do me a favour and read my posts properly. You'll note I've not even said anywhere that you're wrong - I've simply said that the word "torque" is a broader term than the simple mechanical property, and the readers understand it as such.

There are several terms used when talking about cars that have different meanings depending on whether you're using it literally or not. When people talk about "push" when driving a car I don't assume there's someone behind pushing the car along, because I'm not a cretin and I understand that when used in context it's another word for understeer. Ditto "horses" when referring to horsepower. I don't literally think it means there are horses moving the car. "Torque" is another one of those terms. And you're still being pedantic about it.

Words take on new meanings all of the time and the description of torque from the perspective of your Bum dyno is perhaps not the correct way to describe but is a way we all understand.

^ This man understands 👍

 

[Denilson]

Well, if people refere to torque and mean something else, that's nothing I can do anything about I'm afraid.
It's much better to use the terms in the correct way when discussing physics.
What you, or anyone else mean when you say "torque", if you don't actually talk about torque is nothing I can do anything about.
Things can be mixed up pretty bad.
I've always said that I'm refering to physics in my posts. If you don't like that, well, it's not much I can do. Sorry.

 

[homeforsummer]

I've always said that I'm refering to physics in my posts. If you don't like that, well, it's not much I can do. Sorry.

It's not about liking it or not. Your very first post on the matter was all about why people use the word "torque" in the "wrong" way:

I'm getting tired of all the automotive journalists that always refer to the "torque" when testing cars, as though the torque number alone could tell you anything about a cars performance.

As soon as you put it like that, then you open your post up to interpretations. Had you not made it about the way in which people refer to torque, then it wouldn't have been an issue in the first place.

I'll quote PAPPACLART again, because he summed it up perfectly:

Words take on new meanings all of the time and the description of torque from the perspective of your Bum dyno is perhaps not the correct way to describe but is a way we all understand.

The issue here isn't the term being misused, tt's your refusal to accept that the word can be interpreted differently and still mean something both to a writer and to their audience.

 

[CSLACR]

CSL, you're somewhat wrong with saying that peak torque isn't peak thrust.

It absolutely is. In fact, if we had a Magical Engine Of Alien Magicality that made the same amount of torque (say, 500 ft-lb) for an infinite RPM range, the thrust curve would be absolutely flat for every gear, just more for lower gears. Same story applies when we've got a flat curve from, say, 2000 to 7000rpm (stealing the range from Denilson). If we can't rev the engine any higher than said 7000rpm, we'd have a thrust curve of flat lines for each gear. If we had, say, a 500hp constant from n (where n = anything above zero) RPM onward with an infinite rev range, thrust would be a parabolic curve downwards, never quite hitting zero nor quite infinity (but could get infinitely close in either direction) regardless of gear ratio.

Point being, average horsepower over the usable operating range = outright speed. Torque is irrelevant. It doesn't actually matter if it's 500 ft-lb at 5252rpm or 250 at 10504 because we've got the ability to multiply torque (at least when speaking from theory, in practice due to drivetrain losses and such it isn't completely true, as losses aren't entirely percentage based).

If CVTs were to become practical for high-output usage, there'd be a field day about being able to tune for a very narrow operating range... Oh and the thrust curve would be a downwards parabola again, seeing as horsepower would be a constant and output torque would be constantly decreasing as gear multiplication decreased, though it'd be stopped at both ends by the possible multiplication of the transmission.

I'll just close with saying... The best transmission keeps the engine as close to peak horsepower as possible as long as possible. The "best" engine would have no torque peak, and power would be linear with RPM. In GT5, however, mainly thanks to how certain things work, the best engine depends on the use of the car.

If racing power limited, it's whatever holds peak power as long as possible. So, as much power limiting as possible.
If racing PP limited, it's whatever has peak power for as narrow of a range as the gearbox can be tuned to hold and very little in any other region of the rev range.

Edit: @niky: That shortcut makes me want to kill people. One would think the easy way of explaining it would be to just say that it uses what power it has extremely efficiently (which is true).

Wut?

I've talked to you about this before, we both fully understand the subject.
I'm completely confused how you're saying "peak torque is peak thrust" and also saying "torque is irrelevant".
If peak torque = peak thrust, maximum acceleration would be achieved by shifting around the peak torque instead of HP, which as you know, is not how to achieve maximum acceleration.. Possibly you're presuming a flat powerband, which doesn't fit my example. (because flat powerbands have peak torque constantly, so there is no way to shift "around" the peak in torque.)

Just one FYI for anyone reading, flat torque curves don't make great powerbands.
Not at all.

👍 to Exorcet, I have some people that need to read that on another site.

 

[Dennisch]

Forget torque and horsepower.

KW's is where it's at.

Just had to bump this one up.

I just found out that on the official Mercedes website (Dutch) they don't tell you how much horsepower the Merc will give you, instead they give you KW and torque.

Ha! I was right. Well, partially.

 

[Watt2159]

Simply put, Torque gets your wheels moving, while Horsepower keeps you moving.....I think it works like that.

 

[Azure Flare]

Horsepower is how hard you hit a wall.

Torque is how far you take it with you.

 

[Denilson]

Simply put, Torque gets your wheels moving, while Horsepower keeps you moving.....I think it works like that.

Insert key -> Turn the key around -> Battery -> Effect (Electric) to the start engine -> Ignition -> Rotation/torque (The combination determines the effect, and the effect is what gets you moving) -> as revs build upp, effect builds up -> Car accelarate.. Due to the effect from the engine (in this case "Bhp").

Horsepower is how hard you hit a wall.

Torque is how far you take it with you.

Can you evaluate on that using below example?

2 identical cars in terms of everything but the engine.
(Same weight, same drag cooficcient, same front area, same body, same materials.. everything.) The only difference is that the owner of Car B mounted a different kind of engine. A larger, more tourquey engine, but that does'nt rev as much as the engine in Car A.

Car A:
Hit the wall going 100 mph.
At the time of the impact, the engine produce 300 lbft @ 6000 rpm.
([300 * 6000] / 5,252) = 343 bhp @ 6000 rpm

So, Car A hit the wall going 100 mph, with a torque of 300 lbft, and 343 bhp at the wheels (Assuming 0% loss of effect thru the drivetrain. For both cars ofc. 👍) @ 6000 rpm.

Car B:
Hit the exact same wall (After it was rebuilt and had the exact same stability as before Car A hit it), going at the exact same speed (100 mph).
At the time of the impact, the engine produce 600 lbft, and 343 bhp at the wheels @ 3000 rpm.
([600 * 3000] / 5,252) = 343 bhp @ 3000 rpm.

At the time of the impact for both cars, the weight, speed, power, drag cooficient, front area, same body, same materials are identical.
How will Car B move the wall further?
Cause if it does, the only thing that separates the 2 cars are the torque number produced in the engine at the time of the impact.

I'm guessing both cars will move the wall an identical amout of distance, despite Car B's torque that's twice the torque of Car A at the time of the impact (300 lbft vs 600 lbft).

 

[Famine]

Just had to bump this one up.

I just found out that on the official Mercedes website (Dutch) they don't tell you how much horsepower the Merc will give you, instead they give you KW and torque.

Ha! I was right. Well, partially.

EU regulation is that cars' power ratings must be given in kW. Any other power unit (PS, hp, Ch, Hk, CV) may be given supplementally.

 

[niky]

The idea of torque moving a wall is kind of... errh.

All that really matters is what gets to the wheels. As here:

The high peaks are peak torque in each of the dozen or so gears shown in this graph. The righthand peak is peak horsepower.

When you trace the plots like this:

Peak torque produces higher thrust in each gear, but the highest thrust at any speed beyond first gear is at peak horsepower.

So, in actuality... if you're making more horsepower, you will be applying more accelerative force to that wall when you hit it, assuming you don't lift off.