aluminum drive shaft - anyone?

[Votlon]

Originally Posted by justatroll

The real point of the thread was to point out physics: Reducing the rotational inertia of the driveshaft will do almost nothing to the acceleration of the vehicle.
At least no noticeable difference as compared to removing the same weight from somewhere else on the car (like the spare tire).
Having a new set of tires shaved will make a much bigger difference.



The only "pissing" I see is from the people who are certain that the physics in their world is different from reality.

but again,
your trying to prove against something that isnt the main benefit of a lighter drive shaft, the point is to reduce the moment of inertia effect

[justatroll]

Originally Posted by Votlon

but again,
your trying to prove against something that isnt the main benefit of a lighter drive shaft, the point is to reduce the moment of inertia effect

And the point that is the main focus: If you want to reduce the rotational inertia of the entire system (for performance gains) the driveshaft is about the absolute LEAST contributor to rotational inertia.


And many have made the argument that "it increases horsepower".


Show me even ONE case of a horsepower increase on a dyno by reducing the mass of the driveshaft, and I will show you a dyno operator that is doing it wrong.

Originally Posted by jsimon7777

He says, pissing on people.

Really! that's all you got? What, Are you five?
(No YOU are)


Thats your definition of "pissing"?!?
What is it called when I actually use an equation? Murder?
Seems pretty pointless that the only thing you have to contribute is "this argument is stupid".
Quit reading then.

[industrial]

Originally Posted by justatroll

And the point that is the main focus: If you want to reduce the rotational inertia of the entire system (for performance gains) the driveshaft is about the absolute LEAST contributor to rotational inertia.


And many have made the argument that "it increases horsepower".


Show me even ONE case of a horsepower increase on a dyno by reducing the mass of the driveshaft, and I will show you a dyno operator that is doing it wrong.







Really! that's all you got? What, Are you five?
(No YOU are)


Thats your definition of "pissing"?!?
What is it called when I actually use an equation? Murder?
Seems pretty pointless that the only thing you have to contribute is "this argument is stupid".
Quit reading then.

Dynos used for tuning cars are the wrong tool for trying to measure the effect of lightened drivetrain. You are reducing the amount of power/time necessary to get everything rotating in the first place. Once the inertia is broken, the effect has already passed you by. Another powerful effect is the moment of inertia effect when turning the vehicle. All things that are ignored by people that discount the viability of this mod. These are hard to measure since you would have to create a model which takes into account the friction of the vehicle in a turn and all the angles/speeds of rotating components in relation to the direction desired.

I'll try and make a simple example for you. The stock drivetrain is a bucket(rotating weight) within a larger container(dead weight). You have a firehose (or in the case of the BRZ, a garden hose) which outputs (HP) the same amount of water. You have to fill the bucket before you can fill the container before you can move. You dump the bucket everytime you shut off the hose (throttle) regardless of what the status of the container is. Every little micro correction in the throttle is manipulating this bucket. So reducing the size of this bucket will help get you moving in less time. The effect isn't huge but it's definitely noticeable. We are talking about fractions of a second. There are people that argue the benefits of 1-4 millisecond differences in monitor response time for gaming so humans are very sensitive to input lag.

The size and effect of the bucket cannot be measured by measuring the flow of the hose.

I can't think of a simple example for how moment of inertia works in regards to a moving car.

[justatroll]

I'm not arguing that it makes no difference on the track or even a drag race.
In fact it was calculated that replacing the DS with a magical one that weighs zero pounds made tens of milliseconds of difference in a ~15 second quarter mile.
I'm saying that you cannot measure a hp difference on a dyno by replacing rotating mass.

[EAGLE5]

I have seen several a/b tests where the driveshaft was replaced and the cars made significantly more power. It's just facts and logic. Lighter driveshaft equals more power due to frictional changes and decreased mass.

[justatroll]

Originally Posted by jsimon7777

I have seen several a/b tests where the driveshaft was replaced and the cars made significantly more power. It's just facts and logic. Lighter driveshaft equals more power due to frictional changes and decreased mass.

What is a a/b test?
And it is a fact of physics and dyno tests that the rotational inertia of the system plays ZERO of a role in hp measurements.
If you can demonstrate a hp difference based on a change in system inertia then you are doing the dyno measurements wrong.

[nunonuna]

Originally Posted by justatroll

I'm saying that you cannot measure a hp difference on a dyno by replacing rotating mass.

Agree

[cdrazic93]

just. let. it. die. already.

This isnt beating a dead horse, this is making a home inside of it.

[EAGLE5]

Originally Posted by justatroll

What is a a/b test?
And it is a fact of physics and dyno tests that the rotational inertia of the system plays ZERO of a role in hp measurements.
If you can demonstrate a hp difference based on a change in system inertia then you are doing the dyno measurements wrong.

We ran the car on the dyno without. Then we installed. Then we ran the car with. There was a power gain. I mean, your theoretical physics are all great, but in the real world, a lightened driveshaft makes a significant difference in power and torque. It was on a professional dyno. A Mustang, I believe.

[Votlon]

Originally Posted by justatroll

What is a a/b test?
And it is a fact of physics and dyno tests that the rotational inertia of the system plays ZERO of a role in hp measurements.
If you can demonstrate a hp difference based on a change in system inertia then you are doing the dyno measurements wrong.

Yes you can, start a car at a tenth of a throttle then roll onto full, you will notice the LW shaft builds to peak power faster at any point of the rpm curve than the stock shaft. This change would be alot more obvious with a flywheel over a driveshaft, imo

That doesnt mean you get more power from your car, you can just use more of the power you already have

[justatroll]

Originally Posted by jsimon7777

We ran the car on the dyno without. Then we installed. Then we ran the car with. There was a power gain. I mean, your theoretical physics are all great, but in the real world, a lightened driveshaft makes a significant difference in power and torque. It was on a professional dyno. A Mustang, I believe.

If this is true, then you are operating the dyno incorrectly.
A properly setup dyno needs to be compensated for the change in inertia.


"lightened driveshaft makes a significant difference in power and torque"
It absolutely does not.


Do you agree with the following:
1 "HP can be measured at constant angular velocity"
2 "rotational inertia is not a factor in systems rotating at constant angular velocity"

Originally Posted by Votlon

Yes you can, start a car at a tenth of a throttle then roll onto full, you will notice the LW shaft builds to peak power faster at any point of the rpm curve than the stock shaft. This change would be alot more obvious with a flywheel over a driveshaft, imo

That doesnt mean you get more power from your car, you can just use more of the power you already have

"LW shaft builds to peak power faster at any point of the rpm curve than the stock shaft"


I do not understand this statement. A change in rotational inertia cannot make ANY difference in measured horsepower of the engine.
So by saying that the mass of the thing that connects the engine to the diff can in ANY way "make more power" is just plain nonsense.

To understand the concept of how a dyno works:
A dyno measures the torque and the RPM at a discrete point in time. AT STEADY STATE RPM
It then changes to a new RPM and repeats the measurement at steady state.
A dyno IN NO WAY cares how long it takes to get from RPM1 to RPM2.


Can a heavy rotating assembly make a system slower in getting from RPM1 to RPM2 than the same system with a lower rotational mass? - YES
Does a dyno care - NO.


The rotational inertia of the engine & drivetrain does not contribute IN ANY WAY to the measurement of steady state TORQUE.
Because torque can (and by SAE standards) MUST be measured at constant RPM.

[justatroll]

Originally Posted by cdrazic93

just. let. it. die. already.

This isnt beating a dead horse, this is making a home inside of it.

Why, so we can continue to perpetuate the myth that reduced rotational inertia somehow makes more horsepower?

[Votlon]

Originally Posted by justatroll

If this is true, then you are operating the dyno incorrectly.
A properly setup dyno needs to be compensated for the change in inertia.


"lightened driveshaft makes a significant difference in power and torque"
It absolutely does not.


Do you agree with the following:
1 "HP can be measured at constant angular velocity"
2 "rotational inertia is not a factor in systems rotating at constant angular velocity"



"LW shaft builds to peak power faster at any point of the rpm curve than the stock shaft"


I do not understand this statement. A change in rotational inertia cannot make ANY difference in measured horsepower of the engine.
So by saying that the mass of the thing that connects the engine to the diff can in ANY way "make more power" is just plain nonsense.

To understand the concept of how a dyno works:
A dyno measures the torque and the RPM at a discrete point in time. AT STEADY STATE RPM
It then changes to a new RPM and repeats the measurement at steady state.
A dyno IN NO WAY cares how long it takes to get from RPM1 to RPM2.


Can a heavy rotating assembly make a system slower in getting from RPM1 to RPM2 than the same system with a lower rotational mass? - YES
Does a dyno care - NO.


The rotational inertia of the engine & drivetrain does not contribute IN ANY WAY to the measurement of steady state TORQUE.
Because torque can (and by SAE standards) MUST be measured at constant RPM.

You make strong points, I guess I need to do a lil more research on throttle response

[cdrazic93]

Originally Posted by justatroll

Why, so we can continue to perpetuate the myth that reduced rotational inertia somehow makes more horsepower?

or, somehow they reverse trolled you so hard, you begin to question whether or not they understood you, but they wanted to argue with you in the first place.

If the math is right, and the physics is right (...which it is) and you know it to be a myth, and they still dont get it, not your fault.

Like certain canidate supporters. You provide facts and it doesnt do a lick of difference. Law of diminishing returns tells you that youre wasting your time.