Anyone have a hp.vs.tq.vs.accel chart?
06-17-2004, 05:17 PM
#16
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if you look at the units of measurement you can see that torque is momentary (in lifting weights that would be the equivalent of lifting alot of weight for a short time), HP is more sustained (long lasting power).
(The reason for torque being momentary is because it is not a function of RPM. HP is a function of RPM)
This makes sense since Trucks are high in torque they are made to haul alot of heavy stuff, but theyre not very fast.
Alot of times a car with alot of HP isn't as fast as a car with alot of torque, the reason for this is because cars with peak torque usualy have a nice flat HP curve, where as the car with the peak hp has just that; peak hp, with a very small power band
(The reason for torque being momentary is because it is not a function of RPM. HP is a function of RPM)
This makes sense since Trucks are high in torque they are made to haul alot of heavy stuff, but theyre not very fast.
Alot of times a car with alot of HP isn't as fast as a car with alot of torque, the reason for this is because cars with peak torque usualy have a nice flat HP curve, where as the car with the peak hp has just that; peak hp, with a very small power band
06-17-2004, 05:41 PM
#17
Burning Brakes
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yeah but when you are racing you stay in a small power band. On the track noone cares what our cars do below 4k rpms because you are never in that rpm. You shift at 6.5k and that drops you down to about 4k rpms. So who cars if your car is a dog below that, on the track that is.
Regards,
John
Regards,
John
06-17-2004, 06:22 PM
#18
Drifting
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Perry, here is your data as graphed in excell.
Better than I expected correlation. How did you record this data?
I had to adjust the scaling a bit to make everything fit nicely on the graph, so that acceleration is not in any particular unit...
Better than I expected correlation. How did you record this data?
I had to adjust the scaling a bit to make everything fit nicely on the graph, so that acceleration is not in any particular unit...
Last edited by JustinL; 06-17-2004 at 06:42 PM.
06-17-2004, 07:13 PM
#20
I wasn't countering iwhat you wrote. The 2 rpms comment comes from the from the fact that the HP and Tq curves at at 5252 rpms (you wrote 5250). That's why I prefaced with it being nitpicky. 
That's why I wrote that increasing RPMs is the only way to increase HP exclusivley. Without increasing RPMs, you are increasing torque (HP increases are a by-product).
Gordon, we're saying the same thing in different ways
Daniel
Increasing flow increases torque and that will in turn also increase the hp.
That's why I wrote that increasing RPMs is the only way to increase HP exclusivley. Without increasing RPMs, you are increasing torque (HP increases are a by-product).
Gordon, we're saying the same thing in different ways
Daniel
Originally posted by gmonsen
Daniel,
First I don't know if its your typing or what, but I don't understand the formula you presented. At least not the "2 rpms is insignificant though". In almost all meangingful ways, hp is not a number that should be focused on, since it is a second order derivative of torque and rpm. If that's what you mean by insignificant, I agree.
Second, I said that there are 2 ways of increasing hp: more flow or more rpm. You state that increasing rpm just increases hp and that's generally right and entirely in line with what I said. Increasing flow increases torque and that will in turn also increase the hp.
I may have otherwise misunderstood you?
Gordon
Daniel,
First I don't know if its your typing or what, but I don't understand the formula you presented. At least not the "2 rpms is insignificant though". In almost all meangingful ways, hp is not a number that should be focused on, since it is a second order derivative of torque and rpm. If that's what you mean by insignificant, I agree.
Second, I said that there are 2 ways of increasing hp: more flow or more rpm. You state that increasing rpm just increases hp and that's generally right and entirely in line with what I said. Increasing flow increases torque and that will in turn also increase the hp.
I may have otherwise misunderstood you?
Gordon
06-17-2004, 07:29 PM
#21
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Justin- I kind of stumbled across this, but excel lets you have two separate y-axis. Right click, format data series, axis tab, plot on secondary axis. Wish somebody had told me about 5 years ago. If you already knew this, my bad.
06-17-2004, 07:50 PM
#22
Drifting
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Originally posted by rage2
hehe it was done with GTECH Pro, which measures acceleration and calculates torque and hp from that information.
hehe it was done with GTECH Pro, which measures acceleration and calculates torque and hp from that information
.
Ben- yeah I just whipped that up quick and I forgot how to use the secondary axis so I just fit it manually.
Justin
06-17-2004, 08:11 PM
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If it was done with Gtech then the torque measurment presented is rather useless (since Gtech measures acceleration, and then from that and from weight deduces the amount of torque)
06-17-2004, 10:58 PM
#24
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Surprise surprise: the acceleration of the car in the absence of the wind resistance is proportional to the (wheel) torque and inversely proportional to the mass (weight) of the car. The proportionality factor is a constant times the number of revolutions of the engine per distance unit traveled (i.e. a function of the gear chosen, the differential gear ratio and the rolling circumference of the tires).
It is simply derived from Newton’s 2nd law F = M*a => a = F/M applied on the interface between the tires and the road.
GtechPro does not take wind resistance into account when calculating the HP & TQ, hence the good correlation you seen on your graph. This also means that GtechPro grossly underestimates the delivered HP & TQ at higher speeds.
Laust
It is simply derived from Newton’s 2nd law F = M*a => a = F/M applied on the interface between the tires and the road.
GtechPro does not take wind resistance into account when calculating the HP & TQ, hence the good correlation you seen on your graph. This also means that GtechPro grossly underestimates the delivered HP & TQ at higher speeds.
Laust
Last edited by Laust Pedersen; 06-17-2004 at 11:17 PM.
06-18-2004, 12:42 AM
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Daniel,
Kinda thought so... Wasn't sure about the 2 rpms thing. BTW, I believe the actual calculation is far longer and more accurate than torq x rpm/5252. I just don't remember it...
Gordon
Kinda thought so... Wasn't sure about the 2 rpms thing. BTW, I believe the actual calculation is far longer and more accurate than torq x rpm/5252. I just don't remember it...
Gordon
06-18-2004, 07:13 AM
#26
Originally posted by gmonsen
Daniel,
BTW, I believe the actual calculation is far longer and more accurate than torq x rpm/5252. I just don't remember it...
Gordon
Daniel,
BTW, I believe the actual calculation is far longer and more accurate than torq x rpm/5252. I just don't remember it...
Gordon
I'll see if I can find it today....
06-18-2004, 03:52 PM
#27
Race Director
Justin, here's the chart you're looking for...
If you're looking for shift points for maximum acceleration, you pretty much want to redline the 1st three gears. The chart is for a stock 951, so if you have a modified 951, which tends to have a torque-curve that drops faster than stock, the drop in acceleration after the torque-peak might drop below the curve for the next gear on the way up to the torque-peak.
Gordon & Laust's got it with the background math. It's great to see some applications of calculus as math is really worthless and useless until you get to calculus. The thing that's often misunderstood about HP and torque is that they are one and the same, just derivatives and integrations of each other with respect to time. Typically on a dyno, all you can measure is torque, based upon acceleration of a drum of a known mass and diameter. Then this torque is used to calculate the power-curve.
TQ is an instantaneous measurement of rotational force. Once the rotation is canceled out by 1/2 the diameter of the rear tyre, you have a leaner thrust on the ground at the contact patch, but it doesn't have any function of time in it. This might be analogous to a single punch in a bar fight.
HP then is an integration of TQ with respect to time (area under TQ curve). This is basically TQ per second. In the bar-fight scenario, it may be consided punches per second. The more you deliver per second, the more power you have.
Since HP and torque are related, which one is more relevant? Neither really, because they are one and the same with time added. What's more important isn't the peak HP & TQ figures, but the shape of the curves. The quickest acceleration is on a car with the highest average torque-curve over the RPM-range in which it's accelerating. The fastest top-speed goes to the car with the most HP (provided its gearing is matched appropriately to its power-peak). Here's a comparison, let's say we have two cars:
They both have identical HP figures, but which one is quicker? The one with more torque course. Because if you take the TQ figure, multiply it through the gearing, then divide out the radius of the rear-tyre , you get a thrust figure (linear force). At any given RPM, the car with higher TQ, will end up with higher thrust. Imagine this thrust is the same pushing force on the car as if you were behind it pushing on the rear bumper. This leaner Force can then be plugged into F=ma to figure out the resultant instantaneous acceleration at that RPM.
Another way to look at the differences in acceleration would be to compare their areas underneath the torque curve:
If all else is equal, such as weight and gearing, Car-1 would accelerate about twice as quickly as Car-2. You can also calculate how quickly Car-1 would pull away from Car-2 in a drag race by comparing the differences in their torque-curves:
Interesting thing is that if you have enough road and appropriate gearing (5th for Car-1, 4th gear for Car-2), both of them would hit the exact same top-speed since they have the same HP.
If you're looking for shift points for maximum acceleration, you pretty much want to redline the 1st three gears. The chart is for a stock 951, so if you have a modified 951, which tends to have a torque-curve that drops faster than stock, the drop in acceleration after the torque-peak might drop below the curve for the next gear on the way up to the torque-peak.
Gordon & Laust's got it with the background math. It's great to see some applications of calculus as math is really worthless and useless until you get to calculus. The thing that's often misunderstood about HP and torque is that they are one and the same, just derivatives and integrations of each other with respect to time. Typically on a dyno, all you can measure is torque, based upon acceleration of a drum of a known mass and diameter. Then this torque is used to calculate the power-curve.
TQ is an instantaneous measurement of rotational force. Once the rotation is canceled out by 1/2 the diameter of the rear tyre, you have a leaner thrust on the ground at the contact patch, but it doesn't have any function of time in it. This might be analogous to a single punch in a bar fight.
HP then is an integration of TQ with respect to time (area under TQ curve). This is basically TQ per second. In the bar-fight scenario, it may be consided punches per second. The more you deliver per second, the more power you have.
Since HP and torque are related, which one is more relevant? Neither really, because they are one and the same with time added. What's more important isn't the peak HP & TQ figures, but the shape of the curves. The quickest acceleration is on a car with the highest average torque-curve over the RPM-range in which it's accelerating. The fastest top-speed goes to the car with the most HP (provided its gearing is matched appropriately to its power-peak). Here's a comparison, let's say we have two cars:
They both have identical HP figures, but which one is quicker? The one with more torque course. Because if you take the TQ figure, multiply it through the gearing, then divide out the radius of the rear-tyre , you get a thrust figure (linear force). At any given RPM, the car with higher TQ, will end up with higher thrust. Imagine this thrust is the same pushing force on the car as if you were behind it pushing on the rear bumper. This leaner Force can then be plugged into F=ma to figure out the resultant instantaneous acceleration at that RPM.
Another way to look at the differences in acceleration would be to compare their areas underneath the torque curve:
If all else is equal, such as weight and gearing, Car-1 would accelerate about twice as quickly as Car-2. You can also calculate how quickly Car-1 would pull away from Car-2 in a drag race by comparing the differences in their torque-curves:
Interesting thing is that if you have enough road and appropriate gearing (5th for Car-1, 4th gear for Car-2), both of them would hit the exact same top-speed since they have the same HP.
06-18-2004, 04:04 PM
#28
I never notice, anyway
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1 horsepower = 550 ft*lb/sec
horsepower is, as stated before, essentially torque*rpm
youll find that these cars like the nissan maxima, which has 275 flywheel horsepower, still gets beaten by my essentially stock car, which is only maybe 230 hp at the flywheel. you may wonder why, but then when looking at the torque curve, THEN it becomes obvious.
my motorcycle had 40 hp, but it hit that at 12,500 rpm. its torque was about 15 ft*lbs.
dont be fooled by hp numbers, torque is where its at
horsepower is, as stated before, essentially torque*rpm
youll find that these cars like the nissan maxima, which has 275 flywheel horsepower, still gets beaten by my essentially stock car, which is only maybe 230 hp at the flywheel. you may wonder why, but then when looking at the torque curve, THEN it becomes obvious.
my motorcycle had 40 hp, but it hit that at 12,500 rpm. its torque was about 15 ft*lbs.
dont be fooled by hp numbers, torque is where its at
06-18-2004, 05:50 PM
#29
Race Director
Yup, technically, power is force per unit time per unit distance. But since the distance that the force is applied, through the same length lever arm of crank-throws, the same lever arm of 1/2 diameter of rear tyres, distance over which that the force is applied is always equal. Then the only thing that remains the time (or RPM).
A little more on comparing that last picture I posted comparing the torque differences between the two cars. Note that in the low-RPMs, Car-1 has about 3x the torque as Car-2, so it would pull away incredibly fast starting from a stoplight. Only in the upper-RPMs does Car-2 narrow the torque-gap to have about 80% of the torque as Car-1. So the torquey low-revving Car-1 pulls away quickly while Car-2 evens it out in the upper-RPMs, but doesn't catch up or close the distance. This would like a drag race between a '91 MustangGT vs. a Honda Integra Type-R VTEC. They both have about the same HP, but guess which one wins the drag race?
A little more on comparing that last picture I posted comparing the torque differences between the two cars. Note that in the low-RPMs, Car-1 has about 3x the torque as Car-2, so it would pull away incredibly fast starting from a stoplight. Only in the upper-RPMs does Car-2 narrow the torque-gap to have about 80% of the torque as Car-1. So the torquey low-revving Car-1 pulls away quickly while Car-2 evens it out in the upper-RPMs, but doesn't catch up or close the distance. This would like a drag race between a '91 MustangGT vs. a Honda Integra Type-R VTEC. They both have about the same HP, but guess which one wins the drag race?
