I’ve never understood what the difference is.

 

torque is a measurement, horsepower is a calculation using torque... they will always cross at 5252rpm, to calculate horsepower you multiply torque by rpm and divide that by 5252... torque will get you off the line but horsepower is what allows you to keep accelerating

 

https://www.roadandtrack.com/car-cul...que-explained/

 

because you're continuing to make more torque in the upper RPMs (calculated as higher horsepower)

 

torque typically falls off in the top end but that's where the rpm comes into play and you keep accelerating... now if you could hold peak torque through the rest of the powerband that would be ideal

 

Torque is force, but not power. You can have torque, but with no work accomplished. If work is accomplished (i.e. movement), then it's actually power. If a 10 pound weight is applied to the end of a 1 foot wrench on a stationary bolt, then there is 10 lbs/ft of torque applied, even if the bolt does not move. If the bolt does move, then you can factor horsepower from the force and speed of movement.

 

I understand how torque works as in tightening down a lug nut.

I think of HP as how much power the engine has. I'm still confused with the relationship between them. The calculations and descriptions confuse me.

I heard a guy say in a movie say;

Explain it to my like I'm a 6 year old

 

the engine is an air pump.
that pump has a range of rotational speeds where it more- or less-efficiently burns & moves a combination of air & fuel.
the most-efficient range of RPMs is known as your power band & is where you make most of your torque.
horsepower is simply a number calculated from how much torque you make at a specific RPM & gets bigger if the same torque's made at a higher RPM.

if the engine's more efficient at lower RPMs (think diesel), it has plenty of torque to work with but a low horsepower number because it doesn't turn as fast. it doesn't keep accelerating to top because it ain't efficient enough at high RPM to keep making power like it did down low.

conversely, if the engine is more efficient when it spins faster (like a sport bike or rice-burning honda), that small engine doesn't make anywhere near as much working torque as the bigger engine, but since it is able to make that power at high RPMs, it calculates to a much larger horsepower number & can continue accelerating at high RPM because that's where it's making most of its power.

that help?

 

Torque is really just force (lbs) multiplied by distance or radius (ft)
The "power" part in "horse power" is really just force (force starting from the piston combustion) which is torque/radius multiplied by velocity (distance divided by time OR circumference multiplied by RPM at which its traveling at) The key here is movement

Without going into longer calculations, we have to realize that with spinning or rolling forces, we have circumference in order to get wheel RPM or motor RPM - rotations per minute. (This has to be broken down into Pi, and radii in the equations. We are mainly talking about the radii and Pi of the internal parts like crank (and it's rotation) but this basic principle applies to a wheel as well.)

A Scottish engineering, James Watt, determined an "optimal" horse can pull 33,000 foot lbs of work in a minute (or lift 550 lbs by 1 ft in 1 sec). THIS time frame is how horsepower becomes a figure of torque, where they cross at 5252 RPM. This odd number at first glance specifically comes from (Torque X 2 Pi X RPM) divided by 33,000. At 5252 RPM the horsepower goes up, but force goes down and velocity goes up. This is OK though, we want this. Assuming we are NOT staying in one gear (but rather going through the gears) we can sacrifice a little torque up top, for being able to do work more quickly and giving that better acceleration and velocity. This can be manipulated, but this is the general rule. (Also, interestingly, the 5252 thing only happens in emperical units, not in metric. It's a much higher RPM in metric)

You can have a huge diesel motor that operates at 1,000 RPM making 1,000 lb fts of Torque, but only making 100 HP. Conversely, we can have a rev-happy gas motor, that, at the same 1,000 RPM, makes only 100 lb ft of Torque and the same 100 HP. This ALL has to do with engine design: displacement, energy density of the fuel, bore versus stroke (cylinder filling efficiency versus compression, under-square design versus over-square), RPM limit, naturally aspirated versus forced induction, and so on.

In transmission gearing, lower or shorter gears (numerically higher gears) multiply torque significantly and are used for the first gears. However, the rate at which torque is applied is foiled by the above equations. Thus needing to switch to a higher or longer (numerically lower gears) so that you can move UP the RPM band. You don't NEED all that crazy amount of torque as much at higher speeds while you are already accelerating. If you couldn't switch gears, you'd have crazy torque but limited to a really small number in MPH.

We can also add clever tricks such as variable valve lift and/or timing, cam phasing, intake runner length, more efficient transmissions, etc to further manipulate these numbers for "best of both world" scenarios where you get a nice torque and horsepower curve for the desired engine.

We can all agree that sometimes more power (force x velocity) is just better because it gives more acceleration (increasing change or delta in speed)

One more thing: dynos get torque by measuring the force of the tires applied to the drum. It's calibrated first by physics parameters, then secondly by other parameters such as SAE corrections, and drum resistance (Mustang dynos versus Dynojets). Then horsepower is calculated (or calculated simultaneously, rather)

 

There's an old saying: 'Torque' is what gets you off the starting line (first); 'horsepower' is what takes you to the finish (first).

 

Exactly.

OP - this is as simple and basic of an explanation as possible.

 

I think I have it now. I bet there are lots of guys that don't understand it either.

Maybe they just don't want to ask because they will look stupid.

Again, Thanks

 

High Torque on the street is what makes a car harder to drive without slipping the rear end out all over the place.. that's the number that will get ya'

 

Torque, rotational velocity, and power output are just a mathematical formula.

Power = torque * rotational velocity

Horsepower = torque in lb-ft * rpm / 5252

Anything that you can express in torque at a certain RPM, you can express in horsepower at a certain RPM. Torque curves (torque versus RPM) give you the full picture. We tend to overlay horsepower on top but we don't particularly have to.

If you were to recall your physics class and draw a free-body diagram, it would show you the forces that matter. Torque translates to the force parallel to the ground (tangent to your wheels). Other forces are air resistance (a formula based on your car's specific setup and your velocity), the force due to the friction of your tires against the ground, and then all the combined force of all the friction and other inefficiencies in your drivetrain (everything from friction in the engine to friction in the wheel bearings, basically.) Chassis dynos take the last portion into account. You also have the force of gravity on an incline which plays into account if you are not on a perfectly flat surface (in other words, don't forget your gravity and your normal force).

Add up all the forces at a given speed and engine RPM and engine load and you get F = ma, where m is the mass of your vehicle and a is the acceleration you will see.

Note that dynos (engine brakes, chassis dynos) all load up your engine differently than in real life; they aim to see your maximum output, whereas you are almost never driving at your maximum output -- basically only at full throttle, when nothing is slipping, and when you're fully "spooled up."

Peak torque and horsepower figures are mostly there to sell cars. Area under the curve matters far more. High torque at 2000 RPM flat all the way to redline will feel and perform very differently than a linear-but-not-flat curve where, say, you see a higher torque at 5000 RPM but a lower torque before 4000. Two wildly different torque curves may show very similar peak figures but require significant changes in driving _and_ in hardware (for example, max torque at stall -- what you usually get with electric engines -- require way beefier drivetrain components to deal with the shock load and a better traction control system, versus, for example, a 991 GT3 which builds torque up and up and up but acts like a pussycat around town and won't break tires loose if you give it just a little too much gas.)

 

Horsepower is how fast you hit the wall
Torque is how far you move the wall

 

In the TQ vs HP conversation we should drop the "horse". In today's society it means nothing... except maybe to the Amish.

By changing the math you could have an equally valid number using say.... Man or Dog.
Engine spinning 750 rpms and making 30 ft lbs TQ = 4"Horsepower"
Engine spinning 750 rpms and making 30 ft lbs TQ = 9 "Manpower"
Engine spinning 750 rpms and making 30 ft lbs TQ = 13 "Dogpower"

IMO we car guy / knuckle draggers should simply look at three things to determine performance.
1. Torque curve
2. Multiplication / division of that TQ (transmission, rear gear, tire diam)
3. Friction that robs the TQ.

With those three you'll understand everything you need to know to help you spec rations, tire sizes, and shift points.

 

Like a 6 year old? Ok here goes... the more horsepower you have then better. Also, The more torque you have the better. That’s all the explanation I can offer haha

 

"Horsepower is how fast you hit the wall
Torque is how far you move the wall"

I don't agree with this analogy because mass plays a huge factor here
Imagine vehicle A is a huge diesel truck and vehicle B is a small sports car.
They both run the 1/4 mile in 10 seconds at 130mph and run into two separate, but identically-built walls. Let's say these walls are on tracks that allow the wall to move very far back.
Because force = mass x acceleration, and the acceleration is the same between both vehicles, the truck will have more force because it has more mass. More force acting on the wall will ultimately move the wall more



If we talk about two cars with the same mass:
Car A with 100 hp and 200 tq and car B with 200hp and 100tq
Car B (although down on torque) will still give a higher top speed (more power = more work done, faster) and thus have more acceleration.
This will generate more force against the wall as well if we are talking about flat-out runs for each car

 

see above quote.

 

It's a lot like measuring area and volume, but less intuitive because the dimensions are force, distance, and time, rather than just distance in three directions.

There are scenarios where one is more useful than the other. If you want to understand the force on a part in the engine or drivetrain, torque is usually the figure that matters. If you want to understand 0-to-60 or quarter-mile performance, power is what matters (and weight, of course).

Gearing changes torque, but gearing doesn't change power.

Torque at the wheels is what matters. Torque at the crank is highly overrated IMO, because gearing can make up for it. You can usually shift down if you want more torque at the wheels (unless of course you're all already in first gear). If shifting down doesn't solve your problem, then your problem isn't lack of torque, and it's probably lack of power.

Torque is also kinda worthless. I can make 400 ft-lb all by myself, without even breaking a sweat. All I need to do is stand on a two-foot lever. See what I mean by worthless? If I'm just standing on a motionless lever, that torque is getting nothing done. For torque to be useful, it needs to be moving. Speed is a multiplier for the usefulness of torque. That relationship is so interesting that we have a word for it: power. Power is, literally, torque multiplied by speed.