HP vs torque

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HP vs torque

Postby everything on Mon Dec 30, 2019 10:26 pm

Can anyone explain it “for dummies”?

Since MA people like to claim physics understanding, maybe someone here can.

The car guys all fail.

If you can get me to understand it, I’ll pay attention to your physics claims. If not, “biomechanics” stays in the same category as woo woo for me as far as the blah blah blah (not anyone’s fault).
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Re: HP vs torque

Postby Trick on Tue Dec 31, 2019 12:18 am

That’s an question for the Neo-MMA guys. We traditionals are more horse and wagon types
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Re: HP vs torque

Postby everything on Tue Dec 31, 2019 9:04 am

Trick wrote:That’s an question for the Neo-MMA guys. We traditionals are more horse and wagon types


lol. shit like "one horsepower is the force needed to lift 33,000 pounds one foot in one minute" and saying torque provides "rotational" force is also not that helpful. You can imagine one poor horse moving a 33lb wagon one foot in one min, and turning a wrench, I guess.

to answer my own question, some people say something to the effect that torque gets that initial rotational force (ultimately tires applied to pavement) going that you feel push against your back. horsepower is then how long/fast that is applied. a high torque truck can pull the heavy wagon but not accelerate so fast. a lotus cannot pull the wagon but can accelerate. so you can feel the effects, but understanding the physics ---- kind of just as impossible as arguing about biomechanics and qi and levers and so on in MA forum posts in my mind. I mean I kind of, sort of, get it. But in actual application, it's difficult to launch my 6 speed manual, fwd Honda, and it's super easy to launch my awd suv. :-\ ;D
Last edited by everything on Tue Dec 31, 2019 9:05 am, edited 1 time in total.
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Re: HP vs torque

Postby Snork on Tue Dec 31, 2019 10:51 am

I'll have a go since I'm here.

Horsepower is (basically) torque times rotational speed. So if you apply a torque (rotational force) to something and it gets some speed you can say you have power. In the case of car engines, you usually hear about it in the opposite direction, a given engine has some horsepower (it's been designed and built and its stats have been measured) and this results in torque and speed at the driveshaft of the engine. The speed you can see (it's rotating), the torque is more difficult, but it's there. This torque/speed then has to be coupled to the wheels of the car to get them to move. Being things that rotate themselves, they too will end up with torque and rotational speed, but to get it from the engine, they have to be connected to it by gearing (transmission). Car engines might have lots of horsepower but usually this just means that they give lots of rotational speed and not much torque. Using different sized gears all linked to together the rotational speed can be dialled down and the torque increased (because the engine is supplying a given power at any time, thanks to the equation above if you manage to decrease the rotational speed by applying a sequence of gears the torque must then go up). After going through the gears to the wheel the torque is increased. In terms of a car starting to move, since they are generally pretty high mass the torque needs to be quite high to get any appreciable acceleration (thanks to another equation, the rotational equivalent of force = mass times acceleration).
A "better" engine is then one which is designed to produce more torque for a given horsepower. This is because even though the rotational speed of the driveshaft might well be decreased, it's still going to be much faster than you want the car to go, the torque at the wheels will be higher from the outset (getting the car moving faster) and less gearing will mean less mechanical losses in getting the torque to the wheels.

I have no idea if that answers your question but Happy New Year anyway ;D
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Re: HP vs torque

Postby windwalker on Tue Dec 31, 2019 11:24 am

everything wrote:Can anyone explain it “for dummies”?

Since MA people like to claim physics understanding, maybe someone here can.

The car guys all fail.

If you can get me to understand it, I’ll pay attention to your physics claims. If not, “biomechanics” stays in the same category as woo woo for me as far as the blah blah blah (not anyone’s fault).


seems very straightforward.



If one can not understand something is it their level of understanding or
the material it's self is targeted at a different level.

"physics" itself requires a certain level of understanding not based on experience
seeking to define observations to make them understandable for others regardless
of experience.
Last edited by windwalker on Tue Dec 31, 2019 11:47 am, edited 2 times in total.
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Re: HP vs torque

Postby everything on Tue Dec 31, 2019 12:20 pm

Snork wrote:I'll have a go since I'm here.

Horsepower is (basically) torque times rotational speed. So if you apply a torque (rotational force) to something and it gets some speed you can say you have power. In the case of car engines, you usually hear about it in the opposite direction, a given engine has some horsepower (it's been designed and built and its stats have been measured) and this results in torque and speed at the driveshaft of the engine. The speed you can see (it's rotating), the torque is more difficult, but it's there. This torque/speed then has to be coupled to the wheels of the car to get them to move. Being things that rotate themselves, they too will end up with torque and rotational speed, but to get it from the engine, they have to be connected to it by gearing (transmission). Car engines might have lots of horsepower but usually this just means that they give lots of rotational speed and not much torque. Using different sized gears all linked to together the rotational speed can be dialled down and the torque increased (because the engine is supplying a given power at any time, thanks to the equation above if you manage to decrease the rotational speed by applying a sequence of gears the torque must then go up). After going through the gears to the wheel the torque is increased. In terms of a car starting to move, since they are generally pretty high mass the torque needs to be quite high to get any appreciable acceleration (thanks to another equation, the rotational equivalent of force = mass times acceleration).
A "better" engine is then one which is designed to produce more torque for a given horsepower. This is because even though the rotational speed of the driveshaft might well be decreased, it's still going to be much faster than you want the car to go, the torque at the wheels will be higher from the outset (getting the car moving faster) and less gearing will mean less mechanical losses in getting the torque to the wheels.

I have no idea if that answers your question but Happy New Year anyway ;D


Hahaha, yeah, I kind of sort of get that. But not really exactly. But thanks for the explanation! Happy New Year!
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Re: HP vs torque

Postby everything on Tue Dec 31, 2019 12:37 pm

windwalker wrote:
everything wrote:Can anyone explain it “for dummies”?

Since MA people like to claim physics understanding, maybe someone here can.

The car guys all fail.

If you can get me to understand it, I’ll pay attention to your physics claims. If not, “biomechanics” stays in the same category as woo woo for me as far as the blah blah blah (not anyone’s fault).


seems very straightforward.



If one can not understand something is it their level of understanding or
the material it's self is targeted at a different level.

"physics" itself requires a certain level of understanding not based on experience
seeking to define observations to make them understandable for others regardless
of experience.


Yeah I like the Engineering Explained guy, and his videos are obviously cited all the time (Youtube search results, used by car magazine sites), but it is not really the "for dummies" type of explanation. Maybe for people with some basics of engineering. Getting beyond the basic idea, it gets more confusing. For example, a lot of dyno curves for a specific car will show a fairly flat torque curve and a fairly linear HP curve with increasing rpm. But I haven't seen much explanation of that other than circular logic based on a definition of HP and torque and 5252 rpm. There is more HP because there is more rotational speed, but I don't follow the actual meaning of that statement. It gets easier to look at specific cars and their power characteristics. For example here is a graph for a recent year Civic.

Image

In actual use, if the torque is pretty "flat" but HP increases, why does anyone need to rev this car for acceleration? Is the driver trying to use that peak torque higher in the range (6250ish rpm in this case) so has to rev this car up a bit higher for acceleration? Why can't the shift point just stay at 3-4k rpm where torque is already pretty high before dropping slightly? For example. In either case, after the peak, torque drops, so other than keeping in a gear so the next gear is around the peak again soon, is there any reason to not shift sooner? Shouldn't people pay way more attention to the torque curve and NOT the HP curve? It seems like that is the case and the marketers and the users themselves are conflating two concepts and metrics. Which would lead me to believe the users also don't really understand the two. It wouldn't surprise me.
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Re: HP vs torque

Postby windwalker on Tue Dec 31, 2019 12:44 pm

everything wrote:
In actual use, if the torque is pretty "flat" but HP increases, why does anyone need to rev this car for acceleration? Is the driver trying to use that peak torque higher in the range (6250ish rpm in this case) so has to rev this car up a bit higher for acceleration? Why can't the shift point just stay at 3-4k rpm where torque is already pretty high before dropping slightly? For example. In either case, after the peak, torque drops, so other than keeping in a gear so the next gear is around the peak again soon, is there any reason to not shift sooner?

Shouldn't people pay way more attention to the torque curve and NOT the HP curve? It seems like that is the case and the marketers and the users themselves are conflating two concepts and metrics. Which would lead me to believe the users also don't really understand the two. It wouldn't surprise me.


Never quite understand the fixation with what others understand or not.
The end user only needs to understand to their level of use.

Seems like you've answered your own question about shift points and why

best wishes for the new yr.... :)

CVT transmissions solve all the problems you've mentioned while being biased towards
fuel economy..
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Re: HP vs torque

Postby Snork on Tue Dec 31, 2019 3:35 pm

For example, a lot of dyno curves for a specific car will show a fairly flat torque curve and a fairly linear HP curve with increasing rpm. But I haven't seen much explanation of that other than circular logic based on a definition of HP and torque and 5252 rpm. There is more HP because there is more rotational speed, but I don't follow the actual meaning of that statement


Internal combustion engines are better at producing RPM than torque. This is basically because torque is force time distance on the lever (as shown in the video) but the lever distance is small and the force (basically the controlled explosions in the combustion engine) is also pretty small (as the explosion is small). As you rev the engine (to demand it produce more power) you get more explosions per second so the rpm increases but the lever distance in the piston doesn't change and the force exerted on it by each little explosion doesn't really change (although you do get more) so the torque tends not to go up more. What this means is that if you attach a wheel directly to the engine drive shaft you can get the wheel spinning at 1000 mph but it won't move the car along as it is not generating enough torque (force) to accelerate the car as the mass of the car is so high (force = mass times acceleration again). So you end up relying on the transmission/gearing to increase the torque at the expense of the rpm, but the rpm is so high that decreasing it doesn't matter for practical purposes. Different types of engine work better for this, for example electric motors are usually pretty good for torque but there's a lot of different types/configs.

In actual use, if the torque is pretty "flat" but HP increases, why does anyone need to rev this car for acceleration?


Acceleration is related to mass and force and the force ultimately comes from the torque the engine and gears can produce. If the torque is flat and you want to quickly accelerate the car or pull a heavier load then you might need a lot more torque than the curve gives and the only way to get it if the torque curve produced by the engine is flat, is to rev the engine to produce more RPM and pass that RPM through the gears which will then try to convert out more torque which will translate to more acceleration for the mass you are trying to shift.

Is the driver trying to use that peak torque higher in the range (6250ish rpm in this case) so has to rev this car up a bit higher for acceleration? Why can't the shift point just stay at 3-4k rpm where torque is already pretty high before dropping slightly? For example. In either case, after the peak, torque drops, so other than keeping in a gear so the next gear is around the peak again soon, is there any reason to not shift sooner?


I've had too much champagne to attempt this at the moment
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Re: HP vs torque

Postby everything on Wed Jan 01, 2020 9:29 am

LOL, I feel like I'm starting to understand it very vaguely. If I think about a bicycle, maybe it's easier. My legs can only apply so much torque. When I rotate the pedals, I'm applying some of that torque, but trying to apply an amount of it at an increasing rate so that I can accelerate. At a certain gearing, my legs can't rotate any faster to apply this marginal torque (can't rotate that fast compared to the wheel rotation). I upshift and can keep applying that small amount of torque needed to still accelerate a little. Or just make it easier to produce the torque to keep going with smaller marginal amount of work. Maybe that's approximately it?
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Re: HP vs torque

Postby Snork on Wed Jan 01, 2020 11:52 am

When you push down on the pedals of a bike that linear force from your foot is turned into a torque through the mechanical setup of the pedals (a lever at a certain distance from an axle, T = F*d). The lever/pedals are at a fixed distance so there are really only two things you can do to alter the power in that system (P = T*Vr): pump your legs at a faster rate to increase the RPM, or push down harder with your feet to increase the torque. But in practice humans can't easily do that independently, we like to apply a certain force at a certain pedalling rate, it becomes difficult to do otherwise and we run out of stamina. So the bike wheel is connected to the pedals via gears, which conserve the power (with some mechanical losses) but have the benefit of being able to exchange torque for rotational speed (and vice-versa). The incline of the terrain, friction on the ground and air resistance will provide a counter-force to the bike which will try to decelerate it, this is changing all the time, and these counter-forces can become too large to handle by pushing your foot down harder on the pedal. So if you reach a hill you can change to a lower gear and for the bike to go at the same speed you just have to pedal faster, not harder, as the gears are converting some of your faster pedalling into extra torque to counteract the deceleration force (F = m*a, but here the F is F forward - F counter so to have an acceleration of 0 and maintain the same forward velocity you have to provide an increased F forward to match the increased F counter; with the use of gears you have the option of providing this through faster rate of pedalling rather than by pushing harder on the pedals). On an easy terrain with not much friction or incline you won't need as much torque at the pedals to accelerate and so you can use a higher gear, which will overcome the limit on your ability to pedal at a certain rate at the expense of torque at the wheel - the bicycle wheel will spin faster than you are pedalling and will get the bike moving faster. What stops you from being able to go just faster and faster is the counter force due to air resistance, which increases with the bike speed and which will eventually become so great you will not be able to provide sufficient force through hard pedalling or gears to surpass it and create any positive acceleration.
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Re: HP vs torque

Postby everything on Wed Jan 01, 2020 4:03 pm

I think that is a little easier to understand. If we think of the car's engine/pistons as the "legs", I can start to follow the idea. At least torque and acceleration makes some sense.
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