Trying to figure out torque math

[Pringles]

Do I have it right if everything else is the same with 2 engines, but 1 has 1,000 lbs/ft of torque at 1,000 rpm, vs one that has 1,000 lbs/ft of torque at 2,000 rpm. The top speeds are the exactly the same with both engines in the same car, but the first engine that has the 1,000 lbs/ft torque at 1,000 rpm has twice the horsepower, or is it acceleration?

And then if 2 engines with everything else the same, the one engine has a crankshaft that's 2 units longs vs the other engine that has a crankshaft that's 1 unit long, the engine with the crankshaft that is 1 unit long would achieve the same torque at twice the RPM then the engine with the crankshaft that's 2 units long?

This is all with 1 gear ratio of 1.0. Adding gear ratios makes it more confusing.

[Pringles]

I looked at a bunch of maths videos and lectures online but I still don't get it lol :(

[Pringles]

btw what's the difference between torque and horsepower? I don't see the use of both of them when horsepower a function of torque.

[[CAMSO] MrChips]

Originally posted by Pringles:

btw what's the difference between torque and horsepower? I don't see the use of both of them when horsepower a function of torque.

Hoo boy, you want to start an argument with car people, this is how you do it! XD

Let's keep this as simple as possible. Torque is a unit of work - force multiplied by a distance, hence the units of foot-pounds and newton-metres. In other words, it's the amount of energy that an engine is producing, in an instantaneous snapshot.

Horsepower is a measure of power, which is, put in simple terms, how much work an engine can do in a specific period of time. Horsepower is basically, "how much torque did this engine generate in a second?" - foot-pounds per second, basically.

Torque is useful in that it basically shows where an engine is doing work most efficiently, and is directly tied to the engine's optimal airflow characteristics, but that starts to get incredibly complicated, dealing with stuff like volumetric efficiency, airflow resonances and a pile of other factors!

[Swartkin]

Resuming in a brute and not inteligent way:

Torque is force
HP is how much Torque you can generate in a certain amount of time

[Pringles]

this talk about HP being time makes me confused. You have the RPM graph which has the torque and horsepower, but I don't see any time on the graph?

[jkarmy2000]

Time is represented in RPM as it is a unit of 1/time (1 rev./ minute).

[Bruno RuleZ]

Let me intruduce my explanation, this is a really confusing topic, maybe one more comment help you.

Torque = force times distance
it's the force applied by the piston on the crankshaft.

Power = work
It's the amount of work done in an amount of time.

Power is what really matters, doens't matter what engine you have, if it's generating a specific number of horsepower, it will lift/pull a certain weight in a certain time.

Now comes rpm's and flow efficiency.
The engine varies it's capacity for sucking air. If it's too slow, it can't generate enough vaccum, if it's too fast, there's not enough time until the valve closes. So, the peak torque is where all the parts have the better efficiency in letting air inside the cilinder, it's where the bang is bigger, hence, a bigger number on the graphic.
Rpm is a form of frequency, just Like the 60/50hz of your house's electrical supply. In the engine, we measure in revolution per minute. 1.000rpm means that the engine is making 1.000 revolutions at every minute. So, at every revolution we got one or more expansion cycles, it varies on how much cilinders the engine have. More rpm's means more bangs per minute.

I'm trying not to make a too long comment. But the greater torque you have, the greater is the power, because more force is applied. Also, the greater the the rpm, the greater the power, because, the frequency is higher.

Example: a 4 cylinder 2.0 engine
Stock, aspirated: 140hp@6k rpm
Turbocharged: 200hp@6k rpm (the tunning increased the torque, no higher rpm)
Aspirated tuned: 200hp@9k rpm (the tunning increased the rpm, no higher torque)

Think about a semi a and a race car. The semi needs large amount of power in low rpm's to pull weight. A race car needs large amount of power in the lightest engine possible, hence small high-revving.

I hope this helps.

[Swartkin]

Originally posted by Pringles:

this talk about HP being time makes me confused. You have the RPM graph which has the torque and horsepower, but I don't see any time on the graph?

Example
A car with 250NM of torque has 200hp at 5500RPM
Torque= Force
HP= How much Torque you create at a certain amount of time

so giving it at perspective

A truck with 470hp and 2200nm of torque can pull 30 tons of weight
But a Car with 470hp and 520nm of torque can't

If the truck had the car engine, it could still technically have the same top speed as the original engine, because it has the same hp, but it would also not be able to even run the truck properly, because it lacks TORQUE so it doesn't have the strenght to pull that much weight.

[Bruno RuleZ]

Quoting your question:

"the engine with the crankshaft that is 1 unit long would achieve the same torque at twice the RPM then the engine with the crankshaft that's 2 units long?"

Not necessarily. In the question you gave a example of changing the stroke. You need to account this regarding to diameter. But, increasing the stroke, you increase the levering, and the result is more torque. With the same diameter, and the same everything on the engine, the 2 units crank would have more torque than the 1 unit. The rpm the peak torque occurs will vary a lot from what else you have on the engine. Also, a heavier crankshaft tends to rev lower.

[Pringles]

aw, so torque just is how much mass it can pull?? So that means if all vehicles an engine was powering, if the cars had no mass, the torque wouldn't make a difference?? I think I'm understanding!!!

[Swartkin]

Originally posted by Pringles:

aw, so torque just is how much mass it can pull?? So that means if all vehicles an engine was powering, if the cars had no mass, the torque wouldn't make a difference?? I think I'm understanding!!!:lonestar:

not necessarily pull, more of a force of strength in a brute and dumb way to describe it, If you want speed you want HP, if you want strength you want torque
if you really want the math it's this

Horsepower = Torque x RPM / 5,252

So, breaking it down

Horsepower is equal to torque multiplied by where it's the peak power located at the RPM range divided by 5,252

5,252 is a general consense of where the Torque band crosses the HP band, so you divide by it, so let's have an example

HP = 950 LB.FT. x 5200RPM/5,252
HP = 941
This engine has an amazing 941HP.

[Pringles]

why is it 5,252? Is that how something to do with how James calculated horsepower in the first place. So what you're saying is that torque is the amount of horsepower you can get a certain RPM?

[Admiral Obvious]

Originally posted by Swartkin:

Originally posted by Pringles:

this talk about HP being time makes me confused. You have the RPM graph which has the torque and horsepower, but I don't see any time on the graph?

A truck with 470hp and 2200nm of torque can pull 30 tons of weight
But a Car with 470hp and 520nm of torque can't

If the truck had the car engine, it could still technically have the same top speed as the original engine, because it has the same hp, but it would also not be able to even run the truck properly, because it lacks TORQUE so it doesn't have the strenght to pull that much weight.

This isn't correct though due to gearing. If you geared the (presumably smaller) engine to achieve the same amount of power at speed, both will pull the same load at the same rate. The small engine won't like it because you're probably running it higher, but it can be done.

[Admiral Obvious]

Originally posted by Pringles:

why is it 5,252? Is that how something to do with how James calculated horsepower in the first place. So what you're saying is that torque is the amount of horsepower you can get a certain RPM?

Torque is specifically the amount of force generated in one engine turn in the case of vehicle engines. Power is the amount of work done when you multiply the amount of torque by the engine RPM and then doing the division of 5252 to make the units come out to horsepower. If you divided by 9550 you'd end up with Kw, which is the metric measure of power.

[Pringles]

Originally posted by Admiral Obvious:

Originally posted by Swartkin:

A truck with 470hp and 2200nm of torque can pull 30 tons of weight
But a Car with 470hp and 520nm of torque can't

If the truck had the car engine, it could still technically have the same top speed as the original engine, because it has the same hp, but it would also not be able to even run the truck properly, because it lacks TORQUE so it doesn't have the strenght to pull that much weight.

This isn't correct though due to gearing. If you geared the (presumably smaller) engine to achieve the same amount of power at speed, both will pull the same load at the same rate. The small engine won't like it because you're probably running it higher, but it can be done.

So what you're saying is it is correct with no gears? That's exactly what I thought! Nice!