Wheelspin over-rev 7,600rpm
02-10-2010, 11:04 PM
#32
Formula One Spin Doctor
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If you stay wide open throttle with a good rev limiter system ( 2 stage ) the most you should see is max 200-300 rpm bounce over the limit . Even on 1500 bhp engines, I have not seen more than that .......
02-10-2010, 11:12 PM
#33
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Yes.
Fuel-Cut is how the DME does rev-limiting (and overboost protection).
Agreed with just the engine revving. But add the momentum of the drivetrain, and you can see more then 200-300rpm over.
Agreed with just the engine revving. But add the momentum of the drivetrain, and you can see more then 200-300rpm over.
02-11-2010, 06:06 AM
#34
Nordschleife Master
The momentum is what keeps the engine still spinning, but it can never accelerate itself. That is simply not possible. Just because you don't feel heavy de-acceleration doesn't mean the engine is still accelerating.
02-11-2010, 06:09 AM
#35
Nordschleife Master
If the momentum of a mass could accelerate itself it would turn the laws of physics upside down.
That would mean that a bullet from a gun would accelerate itself, that a long jump sporter would gain speed after lift off, that a downhill skiier would accelerate during jumps etc.
That would mean that a bullet from a gun would accelerate itself, that a long jump sporter would gain speed after lift off, that a downhill skiier would accelerate during jumps etc.
02-11-2010, 06:50 AM
#37
If the momentum of a mass could accelerate itself it would turn the laws of physics upside down.
That would mean that a bullet from a gun would accelerate itself, that a long jump sporter would gain speed after lift off, that a downhill skiier would accelerate during jumps etc.
That would mean that a bullet from a gun would accelerate itself, that a long jump sporter would gain speed after lift off, that a downhill skiier would accelerate during jumps etc.
02-11-2010, 07:20 AM
#38
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I can imagine the speed of a car to continue to accelerate in some instances once fuel is cut, and I can see that momentum of the moving parts could continue although on a rapidly abating line.
Isn't this sort of touching on the heavy flywheel influences and perhaps increases torque syndrome?
Isn't this sort of touching on the heavy flywheel influences and perhaps increases torque syndrome?
02-11-2010, 08:10 AM
#39
Nordschleife Master
The problem is that people confuses instant stop of acceleration with instant stop of movement.
The greater the mass the longer the momentum keeps the movement going, but the acceleration will stop immediately. There's no way around it!
Compare with a heavy flywheel. The rate of de-acceleration is just less than a lighter flywheel.
I'm not a physicist myself, but we cannot argue against the laws of physics no matter how you feel when you let of the gas. LOL just give it up..
And as a I said earlier, fuel cut does not occur instantly when you let of the gas! So that is probably what fools you.
The greater the mass the longer the momentum keeps the movement going, but the acceleration will stop immediately. There's no way around it!
Compare with a heavy flywheel. The rate of de-acceleration is just less than a lighter flywheel.
I'm not a physicist myself, but we cannot argue against the laws of physics no matter how you feel when you let of the gas. LOL just give it up..
And as a I said earlier, fuel cut does not occur instantly when you let of the gas! So that is probably what fools you.
02-11-2010, 03:47 PM
#41
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I'm agreeing with Rogue on this one. Sure, in high school physics, the acceleration would stop as soon as the fuel or throttle is shut off. But, in high school physics, we also use "mass-less" string, "friction-less" pulleys, "fluid-less" air, etc.
Real-world physics is a little different. Forgive my Power Point charts, but hopefully this will illustrate how the mass of the components and their inertia (momentum) affects the system:
Real-world physics is a little different. Forgive my Power Point charts, but hopefully this will illustrate how the mass of the components and their inertia (momentum) affects the system:
02-11-2010, 04:08 PM
#42
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Giving this more thought, I think there are also some "relative" and "absolute" issues going on here.
If you're accelerating at 5 feet/second-squared, if you remove the energy from the system, you still have to hit 4 ft/s^2, 3 ft/s^2, 2ft/s^2 and 1 ft/s^2 before you can be at zero ft/s^2 - this time lag is the duration it would take to end your absolute acceleration and reach absolute deceleration.
However, the moment you go from 5 ft/s^2 to 4 ft/s^2, you are decelerating on a relative scale. A lesser rate of acceleration is still deceleration.
If you throw a ball into the air, you are acting on it with a force. Once the ball leaves your hand, it no longer is receiving energy from an outside force. It will start decelerating relative to earth's gravity as it travels higher up it's arc. Eventually, it's deceleration will reach zero, it will be at the apex of it's path, and it will start accelerating as it comes back to earth.
The more force you act on the ball with (harder you throw) the longer it will take for that deceleration to reach zero. Of course, if you change the properties of the ball (make it heavier or less aerodynamic) then the deceleration will reach zero in a shorter time.
If you're accelerating at 5 feet/second-squared, if you remove the energy from the system, you still have to hit 4 ft/s^2, 3 ft/s^2, 2ft/s^2 and 1 ft/s^2 before you can be at zero ft/s^2 - this time lag is the duration it would take to end your absolute acceleration and reach absolute deceleration.
However, the moment you go from 5 ft/s^2 to 4 ft/s^2, you are decelerating on a relative scale. A lesser rate of acceleration is still deceleration.
If you throw a ball into the air, you are acting on it with a force. Once the ball leaves your hand, it no longer is receiving energy from an outside force. It will start decelerating relative to earth's gravity as it travels higher up it's arc. Eventually, it's deceleration will reach zero, it will be at the apex of it's path, and it will start accelerating as it comes back to earth.
The more force you act on the ball with (harder you throw) the longer it will take for that deceleration to reach zero. Of course, if you change the properties of the ball (make it heavier or less aerodynamic) then the deceleration will reach zero in a shorter time.
02-11-2010, 04:22 PM
#43
Drifting
You are ascribing an inertial component to acceleration. This is the fallacy. F=ma... If F=0, then a=0. This isn't a simplification, this is Newtonian physics.
Your ball example is an interesting one. As you stated, once the ball leaves your hand it starts to accelerate downwards (deceleration). The problem seems to be that people have a problem with acceleration dropping to 0 instantaneously. Yes in the real world this doesn't happen because the force on the ball doesn't go from 10N to 0 in an instant. The force applied to the ball falls away somewhat more slowly, but the function F=ma holds true and the acceleration remains a function of the force. Once the ball stops receiving force, it stops accelerating.
Your ball example is an interesting one. As you stated, once the ball leaves your hand it starts to accelerate downwards (deceleration). The problem seems to be that people have a problem with acceleration dropping to 0 instantaneously. Yes in the real world this doesn't happen because the force on the ball doesn't go from 10N to 0 in an instant. The force applied to the ball falls away somewhat more slowly, but the function F=ma holds true and the acceleration remains a function of the force. Once the ball stops receiving force, it stops accelerating.
02-11-2010, 04:25 PM
#44
Nordschleife Master
Van, with that post I take it you changed your mind regarding your previous post.
I would say your top graph is exactly what happens no matter the momentum. But deceleration will be slower. The bottom graph is how it "feels" in real life.
IMHO the mistake you're doing is to illustrate acceleration as line pointing upwards, this make it easy to confuse acceleration with absolut speed. Acceleration is somewhat linear but the absolut speed is going up. The red line in the second graph is a good illustration of absolute speed of the car/object.
Acceleration stops instantly but since we have a lot of momentum we the rate of deceleration is very slow which makes it feel like we're travelling forward with unchanged speed.
Just look at any datalog from the track where you see speed. Even if I change gear in 0.2 sec I'm loosing speed during that time. If momentum would keep my car acceleration that would not happen. That is why a DSG gearbox is able to cut acceleration times...
I would say your top graph is exactly what happens no matter the momentum. But deceleration will be slower. The bottom graph is how it "feels" in real life.
IMHO the mistake you're doing is to illustrate acceleration as line pointing upwards, this make it easy to confuse acceleration with absolut speed. Acceleration is somewhat linear but the absolut speed is going up. The red line in the second graph is a good illustration of absolute speed of the car/object.
Acceleration stops instantly but since we have a lot of momentum we the rate of deceleration is very slow which makes it feel like we're travelling forward with unchanged speed.
Just look at any datalog from the track where you see speed. Even if I change gear in 0.2 sec I'm loosing speed during that time. If momentum would keep my car acceleration that would not happen. That is why a DSG gearbox is able to cut acceleration times...
02-11-2010, 04:29 PM
#45
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Giving this more thought, I think there are also some "relative" and "absolute" issues going on here.
If you're accelerating at 5 feet/second-squared, if you remove the energy from the system, you still have to hit 4 ft/s^2, 3 ft/s^2, 2ft/s^2 and 1 ft/s^2 before you can be at zero ft/s^2 - this time lag is the duration it would take to end your absolute acceleration and reach absolute deceleration.
If you're accelerating at 5 feet/second-squared, if you remove the energy from the system, you still have to hit 4 ft/s^2, 3 ft/s^2, 2ft/s^2 and 1 ft/s^2 before you can be at zero ft/s^2 - this time lag is the duration it would take to end your absolute acceleration and reach absolute deceleration.
The absolute second that the energy that is causing acceleration is removed the acceleration falls to zero, and, in the real world it will go past zero to a negative number due to friction.
Acceleration is the measurement of the rate of change. Think about the words for second – it is not a measure of how fast you are going.
An acceleration rate of zero ft/s^2 means that you are traveling at a constant speed (as long as direction does not change).
It really is the first graph…..for acceleration