Torque vs. HP
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Re: Torque vs. HP
There's an article I came across that loosely associated Horsepower as the "time" component of the HP-Torque relation thus making the equation a tad bit easier to understand. (Source: dmiessler.com | study | horsepower)
If I understood the article correctly,
Since Torque and HP are related as such:
HP = (TQ x RPMs) / 5252
High torque at *low* RPMs mean lower horse power.
Surposedly we simplify the thinking to 1 single RPM.
500NM of torque but only runs at 1RPM
300NM but runs at 2RPM (thus it's able to do 2 revolutions per unit)
The 300NM car will have more power since it's doing more revolutions in the same time period.
Please correct me if I'm wrong.
Cheers.
There's an article I came across that loosely associated Horsepower as the "time" component of the HP-Torque relation thus making the equation a tad bit easier to understand. (Source: dmiessler.com | study | horsepower)
If I understood the article correctly,
Since Torque and HP are related as such:
HP = (TQ x RPMs) / 5252
High torque at *low* RPMs mean lower horse power.
Surposedly we simplify the thinking to 1 single RPM.
500NM of torque but only runs at 1RPM
300NM but runs at 2RPM (thus it's able to do 2 revolutions per unit)
The 300NM car will have more power since it's doing more revolutions in the same time period.
Please correct me if I'm wrong.
Cheers.
leowjulen
Well-Known Member
Re: Torque vs. HP
Horsepower is a unit for the measurement of power (which work divided by time)
Moving a car = work
So for a car to take less time to accelerate than another car of equal weight, more power is needed.
Torque is a measurement of how much force an engine can exert, and has no time component.
An engine that can exert a lot of force (ie. has a lot of torque) is powerful if it can put that force to work in little time.
Hope that helps!
Horsepower is a unit for the measurement of power (which work divided by time)
Moving a car = work
So for a car to take less time to accelerate than another car of equal weight, more power is needed.
Torque is a measurement of how much force an engine can exert, and has no time component.
An engine that can exert a lot of force (ie. has a lot of torque) is powerful if it can put that force to work in little time.
Hope that helps!
Physicist
Well-Known Member
Re: Torque vs. HP
To put Ju Len's explanation in terms of numbers....
Weight
520d = 1595kg for automatic
530i = 1575kg for automatic
Max Torque
520d (340 @ 1200rpm)
530i (300 @ 2500rpm)
Gear Ratio
520d (5.14 / 2.83 / 1.80 / 1.26 / 1.00 / 0.87)
530i (4.35 / 2.50 / 1.67 / 1.23 / 1.00 / 0.85)
Stroke and Bore
520d (90mm by 84mm)
530i (88mm by 85mm)
Power at Max Torque
520d (77.7KW)
530i (142.8KW)
Seeing that the weight differs by only 20kg, its easy to deduce that the 530i will out-accelerate the diesel as the power at max torque is almost double! Gear ratios aren't that far apart either.
titanic;167903 said:
To put Ju Len's explanation in terms of numbers....
Weight
520d = 1595kg for automatic
530i = 1575kg for automatic
Max Torque
520d (340 @ 1200rpm)
530i (300 @ 2500rpm)
Gear Ratio
520d (5.14 / 2.83 / 1.80 / 1.26 / 1.00 / 0.87)
530i (4.35 / 2.50 / 1.67 / 1.23 / 1.00 / 0.85)
Stroke and Bore
520d (90mm by 84mm)
530i (88mm by 85mm)
Power at Max Torque
520d (77.7KW)
530i (142.8KW)
Seeing that the weight differs by only 20kg, its easy to deduce that the 530i will out-accelerate the diesel as the power at max torque is almost double! Gear ratios aren't that far apart either.
Racebred
Core Group Members
Re: Torque vs. HP
This question pops out every once in a while in car magazines too. From what I gathered from them, and the posts above:
Torque = how hard you push
Power = how hard you work.
With the time component like mentioned above, in terms of engine design:
Power = how hard you can burn the fuel, and how fast can air pass through your engine.
torque = how hard you can twist the crankshaft, which is a function of how much you can maintain maximum pressure in the cylinder, and of course having a sufficent piston area to push on.
Above, we also talked about gearing:
It's good to match peak power with max speed. If not, you either run out of gearing with too much power, or you run out of steam before you reach top speed. (playing with gran turismo gearing will let you try it out)
A super high bhp low torque car like F1 with low gearing (but breathes well), or a big torque low bhp truck with high gearing will achieve the same thing, but just gives you a different feel.
I've just read all these in the recent evo mag.
This question pops out every once in a while in car magazines too. From what I gathered from them, and the posts above:
Torque = how hard you push
Power = how hard you work.
With the time component like mentioned above, in terms of engine design:
Power = how hard you can burn the fuel, and how fast can air pass through your engine.
torque = how hard you can twist the crankshaft, which is a function of how much you can maintain maximum pressure in the cylinder, and of course having a sufficent piston area to push on.
Above, we also talked about gearing:
It's good to match peak power with max speed. If not, you either run out of gearing with too much power, or you run out of steam before you reach top speed. (playing with gran turismo gearing will let you try it out)
A super high bhp low torque car like F1 with low gearing (but breathes well), or a big torque low bhp truck with high gearing will achieve the same thing, but just gives you a different feel.
I've just read all these in the recent evo mag.
Re: Torque vs. HP
The high crank torque, low power truck with tall gearing will not achieve the same thing because in the process of gearing up to get to the wheel speed range that you want, you lose wheel torque. Wheel torque is what accelerates. The longer you can sustain high wheel torque, the longer and across a greater speed range you accelerate. Crank torque would be directly proportional to wheel torque if vehicles only had one gear, but this is not the case. Multi-gears have made crank torque almost irrelevant in terms of acceleration.
Low power (regardless of whether it is high or low torque) can only be geared for create high wheel torque at low speed, or low wheel torque at high speed.
High power can be geared for high wheel torque at high speed, or very high wheel torque at low speed, or low wheel torque at very high speed.
High power gives you the freedom to decide how you want things to be. High torque (occuring at a low RPM, yielding low power), does not allow you that freedom because when it comes down to it, there is no real good ability to get work done.
This is why outside of engine longevity and efficiency (fuel consumed per hp per unit time) concerns, talking strictly about acceleration potential, the target is high horsepower across a minimum engine speed range (width). The minimum speed range will occur naturally given average parameters. It is difficult to create a curve that has one sudden power peak. In fact you have to design towards that goal in order to do it. In a few forms of racing, such a peak where you put all your engine is capable of into one narrow engine speed range, is useful.
Racebred;168079 said:
The high crank torque, low power truck with tall gearing will not achieve the same thing because in the process of gearing up to get to the wheel speed range that you want, you lose wheel torque. Wheel torque is what accelerates. The longer you can sustain high wheel torque, the longer and across a greater speed range you accelerate. Crank torque would be directly proportional to wheel torque if vehicles only had one gear, but this is not the case. Multi-gears have made crank torque almost irrelevant in terms of acceleration.
Low power (regardless of whether it is high or low torque) can only be geared for create high wheel torque at low speed, or low wheel torque at high speed.
High power can be geared for high wheel torque at high speed, or very high wheel torque at low speed, or low wheel torque at very high speed.
High power gives you the freedom to decide how you want things to be. High torque (occuring at a low RPM, yielding low power), does not allow you that freedom because when it comes down to it, there is no real good ability to get work done.
This is why outside of engine longevity and efficiency (fuel consumed per hp per unit time) concerns, talking strictly about acceleration potential, the target is high horsepower across a minimum engine speed range (width). The minimum speed range will occur naturally given average parameters. It is difficult to create a curve that has one sudden power peak. In fact you have to design towards that goal in order to do it. In a few forms of racing, such a peak where you put all your engine is capable of into one narrow engine speed range, is useful.
Re: Torque vs. HP
Dear Axl Ang Gu Kway, that analogy is not accurate lah.. if you take your time to get up to speed and you're cruising at 30km/h on your bike, that does not mean you're doing more work than when you were pedalling your little heart out trying to accelerate the bike the quickest you could from 0-20km/h. Yet at an easy 30km/h cruise, you are covering 150% the distance per unit time.
You have to look at torque and RPM. Power already includes both factors.
Dear Axl Ang Gu Kway, that analogy is not accurate lah.. if you take your time to get up to speed and you're cruising at 30km/h on your bike, that does not mean you're doing more work than when you were pedalling your little heart out trying to accelerate the bike the quickest you could from 0-20km/h. Yet at an easy 30km/h cruise, you are covering 150% the distance per unit time.
You have to look at torque and RPM. Power already includes both factors.
Re: Torque vs. HP
Hard to say really but I suppose the optimum shift RPM will probably be different for each gear. So u need two main important pieces of info , ie gear ratios and torque curve chart..I guess there's a myth out there that changing gears at redline get the best acceleration of the car. I personally think understanding the gear ratios n the tq chart are the key but then again, it aint easy to remember it when driving hard on track..
Hard to say really but I suppose the optimum shift RPM will probably be different for each gear. So u need two main important pieces of info , ie gear ratios and torque curve chart..I guess there's a myth out there that changing gears at redline get the best acceleration of the car. I personally think understanding the gear ratios n the tq chart are the key but then again, it aint easy to remember it when driving hard on track..
AC Schnitzer
Well-Known Member
Re: Torque vs. HP
HP is how fast the car hits the wall.
Torque is how far you take the wall with you.
On FI cars, generally the shift points varies depending on gears. On a basic single turbo car where peak torque is usually achieved at 3000-4000rpm and flatline its way to redline, it is better to shift about 200-300rpm into the redline (whichever is allowable before rev cut kicks in) during your first 3 gears (dependant on ratios). As for 4th, 5th or 6th (if 6MT), shift at where your torque curve starts to drop or when the boost tapers down. Reason being that while the first 3 gears still anticipates a drop in torque, it is still making more power as compared to 4th gear onwards due to its gear ratio.
Best thing to do is to do a dyno and study your hp and torque curves along with AFR map. If you are using Dyno Dynamics, make sure that you specifically request for "Shoot Out Mode". If your car is dynoed without shoot out mode, the hp figures can be manipulated. Easy to trick noobs into believing they had gained 50hp when in reality they achieved none. Shoot out mode by itself cost $1500 just for the licence alone.
HP is how fast the car hits the wall.
Torque is how far you take the wall with you.
On FI cars, generally the shift points varies depending on gears. On a basic single turbo car where peak torque is usually achieved at 3000-4000rpm and flatline its way to redline, it is better to shift about 200-300rpm into the redline (whichever is allowable before rev cut kicks in) during your first 3 gears (dependant on ratios). As for 4th, 5th or 6th (if 6MT), shift at where your torque curve starts to drop or when the boost tapers down. Reason being that while the first 3 gears still anticipates a drop in torque, it is still making more power as compared to 4th gear onwards due to its gear ratio.
Best thing to do is to do a dyno and study your hp and torque curves along with AFR map. If you are using Dyno Dynamics, make sure that you specifically request for "Shoot Out Mode". If your car is dynoed without shoot out mode, the hp figures can be manipulated. Easy to trick noobs into believing they had gained 50hp when in reality they achieved none. Shoot out mode by itself cost $1500 just for the licence alone.
goggomobil
Active Member
Re: Torque vs. HP
Unless your engine has an unusual power curve, for max acceleration I think best to shift so that RPM falls to max torque point after you shift up, and this will depend on your gear ratios and how they are spaced.
As for the relationship between torque and HP I think easiest to look at the classical definition of HP which is 550 ft. lb. per second = 1hp. I think in the old days of horses this was thought to be the rate at which a representative horse could do work ( raise a 550 lb weight 1 ft in 1 sec).
So if a horse could work at twice that rate, ie, 550 lb 1 ft in 0.5 second, then it is a 2hp horse, and likewise 1100lb 1 ft in 1 sec also = 2hp etc.
In the case of engine, rate is defined by RPM, which has the units 1/time.
The definition of HP also gives the interesting relationship where torque always equals horsepower at (near enough) 5250 rpm.
goggo
Unless your engine has an unusual power curve, for max acceleration I think best to shift so that RPM falls to max torque point after you shift up, and this will depend on your gear ratios and how they are spaced.
As for the relationship between torque and HP I think easiest to look at the classical definition of HP which is 550 ft. lb. per second = 1hp. I think in the old days of horses this was thought to be the rate at which a representative horse could do work ( raise a 550 lb weight 1 ft in 1 sec).
So if a horse could work at twice that rate, ie, 550 lb 1 ft in 0.5 second, then it is a 2hp horse, and likewise 1100lb 1 ft in 1 sec also = 2hp etc.
In the case of engine, rate is defined by RPM, which has the units 1/time.
The definition of HP also gives the interesting relationship where torque always equals horsepower at (near enough) 5250 rpm.
goggo
Crufty Dusty
Well-Known Member
Re: Torque vs. HP
"Shoot Out Mode" is not foolproof either... the intake air temp probe position can be manipulated although DD threatens to revoke the license of anyone who's caught doing so.
AC Schnitzer;168223 said:
"Shoot Out Mode" is not foolproof either... the intake air temp probe position can be manipulated although DD threatens to revoke the license of anyone who's caught doing so.
AC Schnitzer
Well-Known Member
Re: Torque vs. HP
In that case the operator risk losing his licence.
My understanding is that 3 warnings will be issued prior revoking the licence.
Of cause you have to find an operator who is trust worthy and ethical. The tuner that I use, usually have another tuner to evaluate the results and allow owners to monitor the entire set up of the car on the dyno.
Crufty Dusty;168241 said:
In that case the operator risk losing his licence.
My understanding is that 3 warnings will be issued prior revoking the licence.
Of cause you have to find an operator who is trust worthy and ethical. The tuner that I use, usually have another tuner to evaluate the results and allow owners to monitor the entire set up of the car on the dyno.
Re: Torque vs. HP
If you shift at peak torque or a little after peak torque to try and maximize area under the torque curve, then you end up with highest average crank torque, but when you factor in the gear ratios, your average wheel torque is lower (based on average petrol engine torque/power curves and average gearing gaps) so acceleration is not optimized.
If you shift beyond peak power or at redline in situations where peak power is close to redline, or where power does not fall sharply off beyond peak power, then you maximize area under the power curve and you have the highest average wheel torque. Acceleration is optimized.
You can work the shift points by power based or force based calculations and both in the end are the same, just mathematically different. You can also do it graphically by looking at power curves and knowing gearing gaps, maximize area under the power curve. The general rule though, and almost without exception with modern petrol otto cycle engines, is to shift at redline to maximize acceleration. This is just due to the shape of the curves and the gearing gaps.
CVT requires different strategy but we can leave that out since the system isn't perfected yet and not widely used, and also because the electronics do all the ratio changing automatically and the driver is no longer involved in shifting.
This is true, but often the ideal shift point is past redline. Often we run into redline before we would like to shift, and longevity taking precedence, we are forced to shift at redline.
There are very few modern exceptions to this rule. For every 1 example to the contrary that is found, another 10 can be found in support of it. Pick any production car, with dyno chart, whose gear ratios are published, and it can be shown mathematically.
This has little to do with hp and torque and much more to do with mass, speed, frontal area, chassis strength.
Disagree. If you're doing force based calculation then you have to look not only at resulting crank torque after shift, but consider the new gear ratio you're now in as well to arrive at wheel torque.
It is very common not even to see peak torque RPM on an engine driven for performance - especially racing engines. And racing engines are engines that generally have torque peak closer to power peak, which underlines the point about how maximizing area under the power curve and shifting at redline is as close to a rule as you'll get to in shift point selection, and not shifting at peak torque, or shortly after peak torque.
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I think it is easier to work a real example than to get lost in the fog. I'm sure you'll find most cars favour shifting at redline. Pick a production car that has lots of data published on it and crunch your numbers.... you'll see..
Racebred;168204 said:
If you shift at peak torque or a little after peak torque to try and maximize area under the torque curve, then you end up with highest average crank torque, but when you factor in the gear ratios, your average wheel torque is lower (based on average petrol engine torque/power curves and average gearing gaps) so acceleration is not optimized.
If you shift beyond peak power or at redline in situations where peak power is close to redline, or where power does not fall sharply off beyond peak power, then you maximize area under the power curve and you have the highest average wheel torque. Acceleration is optimized.
You can work the shift points by power based or force based calculations and both in the end are the same, just mathematically different. You can also do it graphically by looking at power curves and knowing gearing gaps, maximize area under the power curve. The general rule though, and almost without exception with modern petrol otto cycle engines, is to shift at redline to maximize acceleration. This is just due to the shape of the curves and the gearing gaps.
CVT requires different strategy but we can leave that out since the system isn't perfected yet and not widely used, and also because the electronics do all the ratio changing automatically and the driver is no longer involved in shifting.
TripleM;168211 said:
This is true, but often the ideal shift point is past redline. Often we run into redline before we would like to shift, and longevity taking precedence, we are forced to shift at redline.
It's not a myth, in fact it is almost a rule with modern petrol engines - especially so with sportier engines.
There are very few modern exceptions to this rule. For every 1 example to the contrary that is found, another 10 can be found in support of it. Pick any production car, with dyno chart, whose gear ratios are published, and it can be shown mathematically.
AC Schnitzer;168223 said:
This has little to do with hp and torque and much more to do with mass, speed, frontal area, chassis strength.
Unless the torque fall off is very sharp, there is no reason to shift early. If it is unclear, it is easy enough to calculate the shift point.
What's important is the shape of the curves. It doesn't matter as much what the actual value is talking strictly in terms of determining shift points. As long as the curves are proportional and accurate, it doesn't matter if they are translated up or down along the Y axis.
goggomobil;168227 said:
Disagree. If you're doing force based calculation then you have to look not only at resulting crank torque after shift, but consider the new gear ratio you're now in as well to arrive at wheel torque.
It is very common not even to see peak torque RPM on an engine driven for performance - especially racing engines. And racing engines are engines that generally have torque peak closer to power peak, which underlines the point about how maximizing area under the power curve and shifting at redline is as close to a rule as you'll get to in shift point selection, and not shifting at peak torque, or shortly after peak torque.
========
I think it is easier to work a real example than to get lost in the fog. I'm sure you'll find most cars favour shifting at redline. Pick a production car that has lots of data published on it and crunch your numbers.... you'll see..
piggyboyz
Core Group Members
Re: Torque vs. HP
Specific to the question posted initially.
The 530i is faster cos the final drive is higher compared to a diesel, which is always much lower.
Also, diesel cannot rev and in this specific model, the 520d got a rev limit of 5k rev when the 530i got a rev cut at 7k.
I don have the final drive of this 2 car but for the 320d against 330i, the final drive is 2.56 against 3.15.
Specific to the question posted initially.
The 530i is faster cos the final drive is higher compared to a diesel, which is always much lower.
Also, diesel cannot rev and in this specific model, the 520d got a rev limit of 5k rev when the 530i got a rev cut at 7k.
I don have the final drive of this 2 car but for the 320d against 330i, the final drive is 2.56 against 3.15.
Re: Torque vs. HP
a very explicit pun intended to the related party(no s) so it can only be you Jack!
axl;168266 said:Yup... I enjoy this kinda thread. Especially when it enables me to (hopefully!) close the gap on track with the Spec C...
a very explicit pun intended to the related party(no s) so it can only be you Jack!
