Mad_Matt
Well-known member
Torque VS HP
Well it funny this comes up in every Diesel Fourm. The answer is in the formula below. I did nto bother to read all the posts so here it goes.
HP = Torque * RPM / 5,252
Unfortunetly that function doesn't tell you what the real-world implications are, like...What does torque actually do? What does HP do? What are HP and torque? How do they work together?Mad_Matt said:Well it funny this comes up in every Diesel Fourm. The answer is in the formula below. I did nto bother to read all the posts so here it goes.
HP = Torque * RPM / 5,252
Hmmm, how's this, work involves torque, but torque does not necessarily produce work.nicklockard said:How would you explain torque and work?
How was that? I just hope my work doesn't get plagerised and end up in every engineering textbook on the planet.nicklockard said:Can you think of a similar visual to the integral example of yours above?
It also shows that if you imaginarily move the fulcrum point far enough in the direction toward the dumbbell end, there is a point beyond which even the 1000# dumbbell won't be able to prick the hair off Jackbombay's head!!!david_594 said:That drawing is amazing.
I'm sorry Jack, but I believe this is incorrect. Your maximum acceleration will always occur at your torque peak because that is where the maximum ability to do work is. In this example we would have to consider that the gear ratios are the same for the 1900RPM and the 3500RPM.jackbombay said:Example: the torque peak for VE TDIs (pre 03') is at 1900 RPM, the HP peak is at 3500 RPM, we all know that our TDIs pull harder at 3500 RPM than at 1900 RPM even though the engine produces less torque at 3500 than 1900.
I hope CarB is faster - it has 2.5 times as much power.jnecr said:Now.. if we took a CVT and put it on two engine that both produced a max torque figure of 200lbft but Car A at 2000RPM and Car B at 5000 RPM. If we have the CVT hold the engines steady at their torque peaks, Car B would be faster because of lower gear reduction making use of the engine's RPM...
Torque peak is irrelevant with regards to work output though, you MUST know the associated RPM of the torque output to determine the amount of work being done, once you have a graph that plots torque vs. RPM you can calculate the "work curve" otherwise know as the HP curve.jnecr said:Your maximum acceleration will always occur at your torque peak because that is where the maximum ability to do work is.
The question was very clear that car A had twice as much torque as car B yet TDIMeister, who is teaching automotive engineering classes in Germany, right? states very confidently that the car with half as much torque at twice the RPM will be exaclty as fast as the car with twice as much torque at half the RPM, why? Because the work output (HP) is the same.TDIMeister said:the answer is simple and it is FACT: They will accelerate at the SAME rate. Argument closed.
Let me get this straight, if there were 2 identical 2002 TDIs that were both stock and one was driving in 3th gear at 1900 RPM and the other at 3500 RPM in 3th and both of them "floored it" you believe that the car that started at 1900 RPM would have a higher rate of acceleration?jnecr said:In this example we would have to consider that the gear ratios are the same for the 1900RPM and the 3500RPM.
You guys are waaayyyy to hung up on torque numbers, sure a weedwacker engine can make 1,000 lb/ft of torque after gearing, AT WHAT RPM??? Lets assume that your weedwacker has a 2 HP engine, if you ran it at it's peak power output through the appropriate gearbox you could get 1000 lb/ft of torque on the output end of the gearbox at 10.5 rpm.Fix_Until_Broke said:A 1Hp weedeater engine can make 200 ft-lbf of torque as can a 5000 hp ship engine - it's all in the gearing.
Sorry to disappoint, but I'm studying it, not teaching.jackbombay said:The question was very clear that car A had twice as much torque as car B yet TDIMeister, who is teaching automotive engineering classes in Germany, right?
Well this starts to become a more difficult question with more variables at play. I don't know exactly how fast a 2002 TDI is operating in 3rd gear @ 1900 RPM (too lazy to calculate it right now), but for the sake of the discussion I'll estimate it to be 30 MPH. At 3500 RPM, the second 2002 TDI, also in 3rd gear, would be running 84 percent faster, or 55 MPH from my initial guesstimate. The drag component at 55 MPH is about 3.4 times greater (1.84^2) than at 30 MPH. Now it is not clear which car will accelerate at the greater rate, because the demand to overcome drag is that much higher.Let me get this straight, if there were 2 identical 2002 TDIs that were both stock and one was driving in 3th gear at 1900 RPM and the other at 3500 RPM in 3th and both of them "floored it" you believe that the car that started at 1900 RPM would have a higher rate of acceleration?
Ooops, its still safe to say that you know more than all (most?) of us about the subject, IMO at least.TDIMeister said:Sorry to disappoint, but I'm studying it, not teaching.
TDIMeister said:on Thursday I am writing an exam in Automotive Engineering 1: Longitudinal Dynamics that will cover the exact same subject.
Yea, I realised that but left it out, the acceleration rate is probably quite close between 3rd at 1900 RPM and 3rd at 3500 RPM, but when one considers the difference in drag there is clearly more power to the wheels at 3500 RPM.TDIMeister said:Well this starts to become a more difficult question with more variables at play. I don't know exactly how fast a 2002 TDI is operating in 3rd gear @ 1900 RPM (too lazy to calculate it right now), but for the sake of the discussion I'll estimate it to be 30 MPH. At 3500 RPM, the second 2002 TDI, also in 3rd gear, would be running 84 percent faster, or 55 MPH from my initial guesstimate. The drag component at 55 MPH is about 3.4 times greater (1.84^2) than at 30 MPH.
jackbombay said:Let me get this straight, if there were 2 identical 2002 TDIs that were both stock and one was driving in 3th gear at 1900 RPM and the other at 3500 RPM in 3th and both of them "floored it" you believe that the car that started at 1900 RPM would have a higher rate of acceleration?
Cute, you really think your car puts more power to the ground at 1900 than 3500 RPM? The fact that there is 3.4 times as much of an aerodynamic penalty at 3500 RPM than 1900 RPM in 3rd gear does not factor into the acceleration you feel in any way?jnecr said:Instantaneous rate of acceleration would be higher on the car that started at 1900 RPM, yes. Get a G-meter and test it out, I guarantee that's what you'll find.
jnecr said:Instantaneous rate of acceleration would be higher on the car that started at 1900 RPM, yes. Get a G-meter and test it out, I guarantee that's what you'll find.
We're all saying the same thing - torque is not revelant, horsepower (force per time) is what accelerates a massjackbombay said:You guys are waaayyyy to hung up on torque numbers, sure a weedwacker engine can make 1,000 lb/ft of torque after gearing, AT WHAT RPM??? Lets assume that your weedwacker has a 2 HP engine, if you ran it at it's peak power output through the appropriate gearbox you could get 1000 lb/ft of torque on the output end of the gearbox at 10.5 rpm.
But the above was completely irrelevant as gearboxes dont make any power they just convert it from low RPM high torque power to some other combination of RPM and torque or vice versa. What the question that started this post is dealing with is torque and power output of an engine before it goes through a gear box, the gearbox, however it is geared will never make more power, sure it can make more torque, but at alower RPM so there is no more power present.
You can leave drag out of it, assume that we are in a vacuum (well.. except for the engine itselfTDIMeister said:Well this starts to become a more difficult question with more variables at play. I don't know exactly how fast a 2002 TDI is operating in 3rd gear @ 1900 RPM (too lazy to calculate it right now), but for the sake of the discussion I'll estimate it to be 30 MPH. At 3500 RPM, the second 2002 TDI, also in 3rd gear, would be running 84 percent faster, or 55 MPH from my initial guesstimate. The drag component at 55 MPH is about 3.4 times greater (1.84^2) than at 30 MPH. Now it is not clear which car will accelerate at the greater rate, because the demand to overcome drag is that much higher.
Without a doubt, the car in second gear will accelerate quicker.The most germane analogy to investigate is to have 2 TDIs travelling exactly side by side and at exactly the same speed at the initial point of interest. One car might be in 3rd gear riding near it's torque peak RPM. Another might be in second and hypothetically at the power peak RPM. IF AND ONLY IF at the very instant they both simultaneously gun the go-pedal, neglecting turbo lag, rotational inertia, etc., the car operating at peak power will have the acceleration edge.
Everything being theoretical I would have to say that the fuel consumption would be the same as I believe you can relate fuel consumption to HP not torque. But then it would all depend on the engines... Is one a V8 and then other an I-4? Who knows?bhtooefr said:Still, I'd like an answer to my question before I vote.
Would Car B use more fuel, assuming that the engines use the same cycle, and use the same type of fuel?
It would mirror the HP curve, really.jnecr said:If you were to plot a logitudinal acceleration curve would it mirror the dyno plot of the torque curve or the horsepower curve?
More power will use more fuel over the same time period - assuming equal thermodynamic efficiencybhtooefr said:Still, I'd like an answer to my question before I vote.
Would Car B use more fuel, assuming that the engines use the same cycle, and use the same type of fuel?
Because of gear redution, you can accelerate faster in nearly all of second gear than you can in third gear... Man I wish somebody with a g-meter could just do some basic measurements...jackbombay said:Do you think Atomic Sushi or any of the other drag racers here wind it up to 4500-5000 RPM when drag racing or do they shift at 2500 RPM to get the revs back down to 1900 as soon as possible as thats where you believe the rate of acceleration is greatest?
An engine spinning at 5000 RPM will have about twice the reciprocating losses as the one spinning at 2500 though. The higher reving car will likely use more fuel, but it would depend a lot on the engines your question is one about effeciencies, X tq at X RPM can have varying efficiency rates depending on type of engine, type/grade of fuel, etc...jnecr said:Everything being theoretical I would have to say that the fuel consumption would be the same...
Using the engine torque data, along with the transmission ratios and the tire diameter, it is possible to calculate the rear wheel thrust in each gear. For the following plot, I have ignored the variations in efficiency of the different transmission gears and have also ignored the effects of windage and oil whipping in the transmission at high speed and have also ignored the rotational inertia of the the engine, tranny, wheels, etc..The five curves in the plot below depict the rear wheel static thrust that is available in each of the five gears. If you divide the thrust in pounds by the weight of the car, you will find the acceleration in g's. The dashed line on the plot depicts typical forces due to rolling friction and aerodynamic drag.
You seem to be avoiding the question, but not intentionally I think.jnecr said:Because of gear redution, you can accelerate faster in nearly all of second gear than you can in third gear... Man I wish somebody with a g-meter could just do some basic measurements...