FBO, Non-Cobrajet Intake Optimal Shift Points, A10

[markmurfie]

Going off just a pure intuition and not giving you an exact acceleration rate.. totally based on the reality of external frictional forces, and also knowing mass doesn't have and effect on acceleration until you get really close to approaching the speed of light, aka relativistic speeds. Which I suppose an indestructible object with a large enough radius could approach, but keeping this based in reality and intuition.

I propose:

With all else being equal, does my car accelerate faster at 10MPH or 100MPH.

Using the same logic for 500RPM and 50000RPM I would say the 100HP and 1000 lbft of torque accelerates faster as that happens at 500RPM.

Anyone reading this, don't be confused, I am a high RPM flat torque guy, low end torque is for losers and breaking things.

Sponsored

 

[markmurfie]

You have been arguing "kinetic energy = m * v^2" this whole time and saying that I must be wrong because I am instead using F=ma. Gillespie's equations also use F=ma. I never said that energy was wrong (you put those words in my mouth); I just wouldn't use that approach myself because it's a less efficient way to get to the answer we're after - maximizing acceleration. Physics is rarely at odds with itself. Let me demonstrate:

I think we can all agree that the engine must accelerate from 6500 to 7500 rpm in both 1st and 2nd gears.

The kinetic energy of the engine's rotating parts is 1/2 * I * w^2.

At 6500 rpm, the KE of the engine's rotating parts is 33,100 ftlb.
At 7500 rpm, the KE of the engine's rotating parts is 44,000 ftlb.

Therefore the change in KE of the engine's rotating parts is 10,900 ftlb, regardless of the transmission gear, acceleration rate, etc. I think we all agree on this.

However, energy is not torque, power, or acceleration, so we must calculate what power it took to add that energy to the engine's rotating parts.

We know from documented acceleration tests that it takes the coyote about 0.31 seconds to pull from 6500 to 7500 in first gear, and just under 0.49 seconds in second gear. Now that we know the delta energy and delta time, we can divide to find the power.

10,900 ftlb/0.31 seconds = 35,200 ftlb/s. Divide by 550 to convert to power and you get 64 hp.
10,900 ftlb/0.49 seconds = 22,200 ftlb/s. Divide by 550 to convert to power and you get 40 hp.

This is power that is being used to add *energy* to the rotating components, that does not contribute to linear acceleration of the car. It affects 1st gear more than 2nd, 2nd more than 3rd, and so on, and therefore will affect optimal shift points.

In post #15 4 days ago, I estimated moment of inertia and calculated power loss in 1st to be 33 hp. Later the same day, I posted that I realized my estimation for moment of inertia was about half of what it should have been. If you double the 33 you get 66 hp, or essentially the same result regardless of which method you use. It's just much easier to calculate and plot the acceleration curves using the a = F/m method and, as I mentioned, Gillespie's method is much cleaner.

I'm sorry, but you are just totally not getting this. Nothing about the mass changes in different gears. Once you apply real world time or distance, frictional forces take over and it all goes out the window.

I've tried to explain what is meant by resistance to acceleration, it's not wrong, its just not obvious, hence it took newton inventing calculus and einstien to come along and bring out E=mc^2.
Its not an external force, its the mass and its physical properties and thats it, leave it there. Because again once you step into reality, its all external forces and what energy they are taking. Unless you are talking about objects floating in space not interacting with any other mass.

I did ask, ARE YOU SURE YOU ARE NOT THINKING ABOUT FRICTION?

It's not a matter of the Dyno not knowing the moment of inertia, it's a matter of not knowing the extra friction car to car. You not going to even get close to the right amount when you do things like compare an old carburetor engine with 200k miles on it and a new Ferrari/McLaren/Porsche engine. Heck even just coyote to coyote will not be the same. Factory freaks are a thing. Even the same engine dyno pull to dyno pulL.

If you wanted an accurate model, you would be looking into things like surface areas between moving and non moving parts. surface area and friction between two moving parts sliding past one another. Then getting more in depth it would be fluid dynamics for the oil film and air friction resistance. Aero dynamics. ect.

 

[engineermike]

I'm sorry, but you are just totally not getting this.

Funny you say that because I directly quoted SAE publications that have been around for years. By saying I am wrong, you are saying the SAE books are wrong. I even asked you to point out which of Gillespie's published equations were incorrect and you were unable to do so. I asked you to demonstrate mathematically how a heavier flywheel would affect acceleration, and you didn't do that either.

At the same time, I showed that rotational acceleration does, in fact, change optimal shift points because it affects acceleration differently in every gear. I did this using the horsepower method, the torque method, Newton's second law (my way), and Kinetic Energy (your way). I posted all of the formulas, substitutions, and outcomes. You have not.

Nothing about the mass changes in different gears.

You keep saying as if I'm disagreeing with you (remember when I asked who you are arguing with?). I've posted the same at least 3 times. However, as Gillespie and others have pointed out, the rotating mass needs to be converted to an "equivalent mass" in order to translate it to linear resistance to acceleration. Stephen Mason explains it very well here using KE=1/2mv^2, as opposed to Gillespie's F=ma (same result either way, as I showed yesterday):

The Effects of Rotational Inertia on Automotive Acceleration (stephenmason.com)

Please read this, as it explains it better than I ever could.

His final equation is mequivalent = mass + moment of inertia x rpm^2.

This is identical to Gillespie's outcome, unsurprisingly.

Neither say the mass is changing, but that the rotating mass's angular velocity does affect the car's linear acceleration rate due to mass "equivalent".

Again, this is not my derivation, but theirs, and they are way smarter than me.

I've tried to explain what is meant by resistance to acceleration,

Gillespie did a great job of that and called it "Inertia Resistance", and his accounts for both linear and angular resistance to acceleration. Sorry, but he isn't wrong.

I did ask, ARE YOU SURE YOU ARE NOT THINKING ABOUT FRICTION?

Every one of my explanations focused on rate of change of angular velocity. I don't know how you could confuse that with friction, which is a function of velocity, not rate of change of velocity.

 

[markmurfie]

KE=1/2mv^2, as opposed to Gillespie's F=ma

These two formulas are not the same thing, you are not getting that.

Look at post 41 instead of just thinking its a rabbit hole. You are literally going against what Newton and Einstein showed the world. Mass does not affect acceleration, we live in a world of friction. Look at a newtons cradle. one ball picked up and only one ball will fly away from the mass. two and two will. The only reason they stop is friction from external forces.

 

[engineermike]

KE=1/2mv^2, as opposed to Gillespie's F=ma

These two formulas are not the same thing, you are not getting that.

No kidding. Unlike you, I did the math both ways. Where did I say they were the same thing? What I said was that they yield the same result. No surprise there.

 

[markmurfie]

No kidding. Unlike you, I did the math both ways. Where did I say they were the same thing? What I said was that they yield the same result. No surprise there.

In the reality of friction, how can they yield the same result. One is describing mass and energy and the other is distance and time? You would have to keep trace of the energy lost to all external forces. The mass its self is not an external force. Even if its rotating.

External forces can be other masses and their accelerations. You hit a wall and the wall doesnt accelerate, but the energy your moving mass has, has to go some where. The deceleration would describe the rate of that energy transfer. Some will be totally redirected and there will be bounce actually accelerating you in the opposite direction.

 

[engineermike]

In the reality of friction, how can they yield the same result. One is describing mass and energy and the other is distance and time? You would have to keep trace of the energy lost to all external forces. The mass its self is not an external force. Even if its rotating.

They yield the same result because, as I said, physics rarely contradicts itself. We are neglecting friction in this math because it acts the same regardless of which math method is used and regardless of your shift points.

I honestly think you realized you were wrong some time back so now you’re just trying to muddy the water.

I asked you what Dr. Gillespie did wrong and you still haven’t answered. If you can’t tell me what is incorrect in his SAE book, then i am right. I asked you to show me your calculations regarding how a mass on the flywheel might affect acceleration and you still haven’t. I posted all of my math and actual results.

 

[markmurfie]

What ever, you don't even understand the math.

You are saying something totally different from what he was saying. 1 pound of rotating mass is like 2 non rotating. That just means it's taking twice the energy.

 

[markmurfie]

how does mass effect a constant acceleration?

I guess "we should compensate for the feathers momentum because it falls slower, to predict the rate is really going to fall."

 

[engineermike]

What ever, you don't even understand the math.

That’s the beauty of using SAE formulas. While I do understand them, I don’t have to understand them in order to use them correctly. I beg you to show me where SAE’s math is wrong. I’ve posted it all. Maybe *you* don’t understand the physics because you didn’t post any actual equations worked out, only snips. I have seen zero evidence that you know how to actually apply any of these formulas.

If you think that Gillespie’s SAE book is wrong, then say so. That’s fine. You’ve all but said it already.

You are saying something totally different from what he was saying. 1 pound of rotating mass is like 2 non rotating. That just means it's taking twice the energy.

It takes more energy to spin up rotating parts because you have to accelerate them both linearly and in rotation, which is indisputable. It takes the same energy to spin them up regardless of gear. However, in higher gears, the time span is longer and power=energy/time, so it takes less power to spin the parts up. Again, same energy, less power. I’ve shown this using the kinetic energy equation. That’s exactly why you would account for that in first gear where the energy must be added to the rotating parts in less time (more power absorbed) as opposed to second gear (less power absorbed). I think we can agree that the engine spins up faster (less time per rpm) in first than second gear. Energy addition is the same, time is greater, so power is less. I really don’t know how to break it down simpler using your energy way of looking at it.

 

[markmurfie]

power=energy/time is wrong. Power=force/time.

Power= energy * time, you even posted it below in your references below.
The dimension of power is energy divided by time.

I can't prove anything to you that you just don't want to see.

Mass and energy are equivalent. (light is the thing that connects them as it has properties of both.)
Force(the transfer of energy) is literally saying two masses pushing against one another. For how long tells you power.

Speed and velocity are equivalent. These are equivalent to power(energy moves at the speed of light, well in empty space anyway)

Torque and acceleration are equivalent. (Light doesn't have acceleration, I know weird there is a speed limit to the universe, but all the other dimensions had limits so it could be expected)

Mass is not speed, velocity, torque, or acceleration.

Acceleration is not mass, energy, speed or velocity

 

[Meatball]

I’ve always liked both of you guys. It’s like watching your nerdy parents fighting prior to divorce…

 

[engineermike]

power=energy/time is wrong.

Hahaha, now I know you’re just messing with me! The very definition of power is energy/time!

References:

https://en.m.wikipedia.org/wiki/Power_(physics)
“power is the amount of energy transferred or converted per unit time“

Power and energy basics - Appropedia: The sustainability wiki
"Energy = Power x Time"

What is power? (article) | Work and energy | Khan Academy
" By definition, one watt [power] is equal to one joule [energy] of work done per second. "

There are literally thousands more references on this...

Power=force/time.

Wrong again! Power = force x velocity. Velocity being distance/time, means power = force x distance/time. You left out distance.

I can't prove anything to you that you just don't want to see.

I've asked you repeatedly to show us your calculations. I'd love to see how you calculate acceleration rate of a car with a known mass, torque, gear ratio, rotational inertia, etc. I mean actual numbers, not snips from the web.

I've also asked flat-out, if you think that Dr. Gillespie's SAE equations are incorrect. Care to give a straight answer?

Mass and energy are equivalent.

Nope. Energy is the ability to do work. Mass at an elevation or at a speed has energy, but there's no way I would describe them as equivalent.

Torque and acceleration are equivalent.

Wrong again! Acceleration at a given mass if a function of thrust. Thrust is a function of torque, gear, mass-equivalent, mass, etc.

Mass is not torque or acceleration.

Finally, correct! Wait, didn't you also say that torque and acceleration are equivalent?

Acceleration is not mass or energy.

Correct again, but if you know the mass, energy applied, and timespan, then you can calculate average acceleration and final velocity very easily.

 

[markmurfie]

I updated the post so you see the whole picture.


What's the weight of 1 lb of lead floating in space? What is the mass?

 

[engineermike]

I updated the post so you see the whole picture.

I reread it. It’s not any better. The first half is dead wrong and the second half is so fundamental that I wonder if you know what we’re even discussing or where the sticking point actually is.

What's the weight of 1 lb of lead floating in space? What is the mass?

0 and 1. What do I win? I had high school physics. I’ve been trying to move the discussion on to college level since the beginning.

Do you or do you not agree with Gillespie’s car acceleration formulas? Why are you having such a hard time answering this simple yes/no question?

Why won’t you post your own math that calculates vehicle acceleration, including the effects of rotional energy? You say my way is wrong, so I did it your way and got the same result. You say that’s wrong too, yet you won’t post up your own calcs. Why? Do you know how to apply your theories mathematically?

Sponsored