hp vs torque
03-14-2005, 01:51 PM
#32
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Yup, its just mathematically related thats all....
Some cases display this in point:
ONE: Gas turbine driving an axial compressor.... Makes 4,000 HP at 14,000 RPM ... thats only 1,500 Ft*Lbs
TWO: Rolling mill motor. Makes 4,000 HP but only at 120 RPM.... thats 175,067 Ft*Lbs
THREE: And for good meausre, my personal favorite.... 635 megawatt steam turbine generator... Makes 868,231 HP at 3,600 RPM... which is 1,266,652 Ft*Lbs
Output shaft is THREE FEET in diameter.... Now thats POWER baby...
Kevin
Some cases display this in point:
ONE: Gas turbine driving an axial compressor.... Makes 4,000 HP at 14,000 RPM ... thats only 1,500 Ft*Lbs
TWO: Rolling mill motor. Makes 4,000 HP but only at 120 RPM.... thats 175,067 Ft*Lbs
THREE: And for good meausre, my personal favorite.... 635 megawatt steam turbine generator... Makes 868,231 HP at 3,600 RPM... which is 1,266,652 Ft*Lbs
Output shaft is THREE FEET in diameter.... Now thats POWER baby...Kevin
03-14-2005, 07:08 PM
#33
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the use of your vehicle should indicate the type of dyno that should be used:
towing = load cell dyno (constant speed driving)
racing = inertia dyno (accelerated launches/races)
anyone agree?
for me, when i installed the comp and injectors on my old truck i was looking for get-up-and-go on the street. i dont tow. i just want to show others what diesels are capable of. tough job to do with a 6 speed though. either way, the dynojet should have been a better suited dyno for me because i was accelerating when using the power.
what about this thought for the inertia dynos...
the rate of RPM increase you see on the street with your current mods should somehow be incorporated into the dyno. in other words, the dyno should be able to adjust the mass, diameter, etc of the rolling drums so as to only allow a vehicle to perform a dyno run with the same rate of RPM increase as seen on the street. clear as mud? if the rotating drums are too heavy (bigillion pounds), would it not be possible to shoot the EGTs through the roof before a full run is complete? i agree the heavy drums would load the truck better, but maybe the drums would load more so than on the street...therefore giving you HP/TQ #s that are higher than what your truck is capable of loading up to on the street? seems like just the opposite is true right now, boost #s are lower as compared to street use because the truck can't load enough on the current inertia dynos.
Pat
towing = load cell dyno (constant speed driving)
racing = inertia dyno (accelerated launches/races)
anyone agree?
for me, when i installed the comp and injectors on my old truck i was looking for get-up-and-go on the street. i dont tow. i just want to show others what diesels are capable of. tough job to do with a 6 speed though. either way, the dynojet should have been a better suited dyno for me because i was accelerating when using the power.
what about this thought for the inertia dynos...
the rate of RPM increase you see on the street with your current mods should somehow be incorporated into the dyno. in other words, the dyno should be able to adjust the mass, diameter, etc of the rolling drums so as to only allow a vehicle to perform a dyno run with the same rate of RPM increase as seen on the street. clear as mud? if the rotating drums are too heavy (bigillion pounds), would it not be possible to shoot the EGTs through the roof before a full run is complete? i agree the heavy drums would load the truck better, but maybe the drums would load more so than on the street...therefore giving you HP/TQ #s that are higher than what your truck is capable of loading up to on the street? seems like just the opposite is true right now, boost #s are lower as compared to street use because the truck can't load enough on the current inertia dynos.
Pat
03-14-2005, 10:13 PM
#34
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wow this thread has turned out to be very informative and confusing.ill ask my buddy for his rpm at those hp and torque #s.will that help out in seeing if somthing was wrong with the dyno machine?i thought he told me 3300 rpms but i may be wrong,must be lower than that?i was just curious why his torque seemed so high compared to otheres with 450hp.i dont want to get those #s from my truck,i was just curious,350hp and 800 would be good for me.at a low rpm{2200}is that possible?anyway thanx for all the great replies.
03-14-2005, 10:44 PM
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Whoa-- glad I missed the meat of the last few posts...
The crux of the issue as *I* see it is whether or not the concept of horsepower is roughly equivalent to the idea of acceleration (which is how we judge "performance").
Kevin has pointed out the numerous flaws is the "number" that a Dynojet produces. But what's being ignored is that fact that the Dynojet tells you something MUCH more important than actual hp, so accuracy isn't really that essential-- repeatability IS, however. The DJ has great repeatability.
In the case of trying to maximize rate of acceleration, all we care about is what I will call "recovery time". In other words, how fast can the engine build RPM under a given load? How fast can it "recover" after being yanked down a in RPM from a gearshift?
If you are testing two engines against a known load (ideally, the same load as they will see in action), the engine that "recovers" more quickly will outperform the other engine-- REGARDLESS of whether or not it makes the "numbers" that the other engine does.
Larry Widmer has told me of numerous projects he's been involved in where the car got faster/quicker as the "number" went down!! (as tested on an engine dyno).
So the flaw isn't so much in the DynoJet as it is in the application of the concept of HP to the concept of acceleration. The formula tells us that HP is a function of TQ and time. But where does it account for a the RATE OF CHANGE in RPM? IT DOESN'T!!
Well, let's ask ourselves what moves the car down the track when we launch? FORCE. F=MA. So produce a change in A for a constant M, we need more F.
In measuring engine output, all we car about is FORCE. This force is TORQUE. The more torque we can sustain against that constant mass, the greater the acceleration will be. That's undeniable.
The problem is that we come into real world limitations as we try to sustain maximum Tq against that constant M. First, we have to rev the engine. The engine's TQ output changes as it winds up. Eventually we have to shift gears. This means we see less tq at the wheels.
Now, when we discuss tq in this sense, we are concerned with a dynamic force-- a force that produces movement. If it doesn't produce movement, it isn't doing any work. I can push against my house all day, but in terms of physics, I have done no work.
Since we are discussing DYNAMIC forces, we have to consider how TQ as a force is affected by the rate of change in engine RPM. *THIS IS THE KEY*
Consider a baseball slugger swinging for the fences. The distance the ball will travel is a function of how much force he can apply to the ball with his bat (assume constant trajectory). If tha bat doesn't change position, it can't apply force to the ball unless the ball hits it by itself. So as the slugger swings, he is constantly changing the position of his bat. The faster he can change the bat's position, the farther he will hit the ball. While this isn't the best example, it illustrates that THE RATE OF CHANGE (bat position here) is correlated to the Force applied (to the ball).
We express the rate of change in bat position as BAT SPEED. In physics, rate of change in position is simply velocity. If I am changing my position by 50 miles in one hour, then I traveled (on average) 50mph.
Think of how significant the concept of "rate of change" is. What would happen if we had a bullet in a gun, and the gunpowder in the case took 10 seconds to burn? The bullet would fall out of the barrel and onto the ground- useless. Because the rate of pressure change is so fast, we have an incredible accelerative force acting on the bullet. Now consider the "kick" generated. In the 10-second case, there is almost imperceptible kickback. In a normal firing, the kickback is significant and noticeable. Taken to an extreme (of a quick pressure rise), you would have the gun explode in your hand.
Another example is air pressure change due to altitude. Normally, we experience this a a gentle popping of the ears as pressures equalize. What if our ears had to adjust to a 3psi pressure difference in only 30nanoseconds? BOOM- ruptured eardrum.
Now we come back to engines and vehicles. We can say that the Force applied is a function of Engine TQ and the rate of change in RPM.
Ive used it before (in other posts), but let's consider the effects of adding a HEAVY flywheel to an engine and "testing" it three ways-- on a load dyno, on an intertial dyno, and at the dragstrip.
On the load dyno, adding the heavy flywheel gives us higher readings. Why? Because all the energy stored in the flywheel on the unloaded phase is released when the truck is loaded. Thus, the readings are skewed high.
On a dynojet, the readings are skewed low with the flywheel because the engine stores energy in it instead of sending it to the wheels.
The dragstrip gives the same result as the DynoJet- skewed low by the flywheel.
This brings me to my closing point (thank God, everyone says). If you are interested in ACCELERATION OF A CONSTANT MASS-- then the Dynojet is the tool you should use.
If you want the ability to sustain progress in the case of a mounting load (AKA pulling), then a Mustang is probably what you should use.
Test your truck in a manner consistent with the type of performance you seek. HP is just a number-- and NO dyno does a stellar job of measuring HP (except maybe Dyno Dynamics) because they are just so many variables.
So if all you want is an accurate number, then a dyno is bound to disappoint. BUT, if you want to measure something MORE IMPORTANT (like recovery time or load handling), then the dyno will be a great to help you.
Remember, a dyno is best used as a "right direction or wrong direction tool".
A dyno is a compass, not a roadmap.
Justin
The crux of the issue as *I* see it is whether or not the concept of horsepower is roughly equivalent to the idea of acceleration (which is how we judge "performance").
Kevin has pointed out the numerous flaws is the "number" that a Dynojet produces. But what's being ignored is that fact that the Dynojet tells you something MUCH more important than actual hp, so accuracy isn't really that essential-- repeatability IS, however. The DJ has great repeatability.
In the case of trying to maximize rate of acceleration, all we care about is what I will call "recovery time". In other words, how fast can the engine build RPM under a given load? How fast can it "recover" after being yanked down a in RPM from a gearshift?
If you are testing two engines against a known load (ideally, the same load as they will see in action), the engine that "recovers" more quickly will outperform the other engine-- REGARDLESS of whether or not it makes the "numbers" that the other engine does.
Larry Widmer has told me of numerous projects he's been involved in where the car got faster/quicker as the "number" went down!! (as tested on an engine dyno).
So the flaw isn't so much in the DynoJet as it is in the application of the concept of HP to the concept of acceleration. The formula tells us that HP is a function of TQ and time. But where does it account for a the RATE OF CHANGE in RPM? IT DOESN'T!!
Well, let's ask ourselves what moves the car down the track when we launch? FORCE. F=MA. So produce a change in A for a constant M, we need more F.
In measuring engine output, all we car about is FORCE. This force is TORQUE. The more torque we can sustain against that constant mass, the greater the acceleration will be. That's undeniable.
The problem is that we come into real world limitations as we try to sustain maximum Tq against that constant M. First, we have to rev the engine. The engine's TQ output changes as it winds up. Eventually we have to shift gears. This means we see less tq at the wheels.
Now, when we discuss tq in this sense, we are concerned with a dynamic force-- a force that produces movement. If it doesn't produce movement, it isn't doing any work. I can push against my house all day, but in terms of physics, I have done no work.
Since we are discussing DYNAMIC forces, we have to consider how TQ as a force is affected by the rate of change in engine RPM. *THIS IS THE KEY*
Consider a baseball slugger swinging for the fences. The distance the ball will travel is a function of how much force he can apply to the ball with his bat (assume constant trajectory). If tha bat doesn't change position, it can't apply force to the ball unless the ball hits it by itself. So as the slugger swings, he is constantly changing the position of his bat. The faster he can change the bat's position, the farther he will hit the ball. While this isn't the best example, it illustrates that THE RATE OF CHANGE (bat position here) is correlated to the Force applied (to the ball).
We express the rate of change in bat position as BAT SPEED. In physics, rate of change in position is simply velocity. If I am changing my position by 50 miles in one hour, then I traveled (on average) 50mph.
Think of how significant the concept of "rate of change" is. What would happen if we had a bullet in a gun, and the gunpowder in the case took 10 seconds to burn? The bullet would fall out of the barrel and onto the ground- useless. Because the rate of pressure change is so fast, we have an incredible accelerative force acting on the bullet. Now consider the "kick" generated. In the 10-second case, there is almost imperceptible kickback. In a normal firing, the kickback is significant and noticeable. Taken to an extreme (of a quick pressure rise), you would have the gun explode in your hand.
Another example is air pressure change due to altitude. Normally, we experience this a a gentle popping of the ears as pressures equalize. What if our ears had to adjust to a 3psi pressure difference in only 30nanoseconds? BOOM- ruptured eardrum.
Now we come back to engines and vehicles. We can say that the Force applied is a function of Engine TQ and the rate of change in RPM.
Ive used it before (in other posts), but let's consider the effects of adding a HEAVY flywheel to an engine and "testing" it three ways-- on a load dyno, on an intertial dyno, and at the dragstrip.
On the load dyno, adding the heavy flywheel gives us higher readings. Why? Because all the energy stored in the flywheel on the unloaded phase is released when the truck is loaded. Thus, the readings are skewed high.
On a dynojet, the readings are skewed low with the flywheel because the engine stores energy in it instead of sending it to the wheels.
The dragstrip gives the same result as the DynoJet- skewed low by the flywheel.
This brings me to my closing point (thank God, everyone says). If you are interested in ACCELERATION OF A CONSTANT MASS-- then the Dynojet is the tool you should use.
If you want the ability to sustain progress in the case of a mounting load (AKA pulling), then a Mustang is probably what you should use.
Test your truck in a manner consistent with the type of performance you seek. HP is just a number-- and NO dyno does a stellar job of measuring HP (except maybe Dyno Dynamics) because they are just so many variables.
So if all you want is an accurate number, then a dyno is bound to disappoint. BUT, if you want to measure something MORE IMPORTANT (like recovery time or load handling), then the dyno will be a great to help you.
Remember, a dyno is best used as a "right direction or wrong direction tool".
A dyno is a compass, not a roadmap.
Justin
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