aluminum drive shaft - anyone?

[stugray]

I simplified it as best I could:

Energy required to accelerate a 2800 lb car to 100 MPH
1270 kg @ 44.7 m/s

Total kinetic energy = ½ MV^2 = 0.5*1270 * 44.7^2 = 1268787.15 joules

Rotational kinetic energy of a spinning cylinder
E-rotational = ½ I w^2 (w is angular velocity in radians/sec I is moment of inertia )

30 lbs driveshaft = 13.6 kg 3" dia (1.5” radius = 3.81 cm = .0381 m) =
I = .0381 * .0381 * 13.6 = .01974 kg.m^2

Stock wheel = 1964.44 mm circumference

@ 100 MPH our wheels are spinning at
@ 44.7 m/s => 44.7/1.964 = 22.75 RPS @ wheels
Final drive ratio = 4.1:1

Driveshaft RPS = 22.75 * 4.1 = 93.275 RPS = 5596 RPM = 35160.7 radians/min = 586 radians/sec

Rotational energy of the spinning driveshaft = ½ I w^2 = 0.5 * .01974 * 586^2 = 3389.32 joules

Energy stored in moving car: 1268787.15 joules
Energy stored in spinning driveshaft: 3389.32 joules

Total energy (NOT COUNTING the energy stored in the REST of the rotating mass) = 1272176.47 joules

For a whopping ratio of 375/1 = .0027 or .27% of the energy in the system.

SO while the engine has stored up a total of 1272176.47 joules in the system, only 3389.32 joules are in the spinning up of the driveshaft.


BRZ gets ~ 16.2 seconds 0-100 mph
That’s 1272176.47 joules / 16.2 seconds or 78529.4 joules/second

OR ~105.36 hp Which for back of napkin calcs is in the ballpark enough (holy shit!).


If you had no energy stored in the spinning of the driveshaft at all: total system energy would be 1268787.15 joules at 100 MPH
If the car delivered the same 78529.4 joules/second it would achieve 1268787.15 joules in 16.156 seconds

So I guess you were all right!
If you reduce the 30 lbs driveshaft to 0 pounds (removing the energy stored in it entirely!) and do otherwise equal runs 0-100 MPH you WILL notice a 44 millisecond difference in a 16.2 second run! Congratulations you are superhuman!

And I was being generous by leaving things out such as the REST of the rotating mass so the actual difference of removing the shaft would be even less.

I never said that it wouldnt make a difference I said that a driver wouldnt be able to TELL the difference.


Shall I repeat the calcs for a 4 pound reduction of the drive pulley?
Which coincidentally would be MORE than the driveshaft since IT spins to ~6000 RPM

And @Shutter beat me to it:

Originally Posted by Shutter

[Hawk77FT]

Originally Posted by stugray

Just FAIL on so many levels.
"Also, explain this: in the wet with the light weight driveshaft I can easily spin the tires, with stock ones, not so much! Same conditions, same tires/wheel combo, same rpm!"

Absolute and utter bullshit.
You are starting with the driveshaft at ZERO RPM and when you "spin the tires" a difference of mass of the driveshaft of a few pounds makes almost ZERO difference to whether you can break the tires loose or not.
Because the rotational inertia change from the point where you havent broken loose to where you DID break loose is ZERO.
So there is ZERO energy stored in the driveshaft in that millisecond where the car is deciding if it has enough hp to break loose or not.
This problem is considered a STATIC physics problem while the rest of this discussion is about dynamics.

(do you also argue over economics with Ben Bernanke?)

Ok Stu, I gave you the static bicycle example before and no answer but that is fine. Now since you know it all, think about this: both bicycles have the same rpm! Say 200 rpm, ok? And we want to get to 500 in the shortest time possible applying the same accelerating force...now which one will get there quicker? I tell you which one: the one with a lighter wheel, the one that requires less energy to reach the next 100's of rpm.

Basically say our cars have about 200hp at the flywheel right? From the flywheel, it has to use some of the power to turn everything inside the transmission which then turns the DRIVE SHAFT which of course then turns the rear end which turns the axles and then to the wheels. The aluminum drive shaft weighs less, and when you're talking about rotational inertia, weight means everything because the less something weighs, the easier it can turn, which then "frees up" power, since it doesnt actually "create" power. In the end, your motor has to use less energy to turn the drive shaft which is a considerably heavy piece of your drive train, and that gain in energy equals an increase in performance. Also, take in consideration the elimination of the joint as well which also helps further.
Same with the flywheel or any component that is light weight: flywheel won't increase horsepower. The typical wheel dyno doesn't measure horsepower...it measures the rate at which the car's engine can accelerate a rotating drum of known inertia. The engine has to accelerate the drive train components as well, so a reduction in drive train rotational inertia will show up on a dyno run as a perceived horsepower increase.
Yes, it might not be super big increase, but as I and few others said, couple it with few more modifications and it would translate in a significant outcome. Seen hill climbing cars going mental fast with all these mods. Anything counts really! Did the calculation using the calculator and it looks like the rotating inertia goes down by the same percentage as the weight of the object!

All in all really, people can spend money on whatever they like!

[Captain Snooze]

@stugray
This question isn't aimed at this thread in particular; it is a physics question. I can't remember too much from my study days

If one is using an inertia dyno is one actually measuring power or is power calculated?
That is, a known mass is accelerated in a known time; is this force,work or power?

Ta.

[industrial]

I afraid you are still missing the point. You boiled down the difference in energy storage over one continuous acceleration. Nobody is saying you gain lots of horsepower with this mod. Assuming your calculations are correct which I'm not going to double check (but really, thanks for doing) for this debate, you come to the conclusion that the difference in a singular straight line acceleration event is 44ms given a weight of 2800lbs and overall duration of 16.2 seconds.

What you are missing is... That 44ms is nearly completely front loaded. So that difference would be largely the same regardless of if you were testing 0-30, 0-2, 0-150, and even 55-60...anytime you change your rate of acceleration (load an unloaded system). You are overcoming the mass moment of inertia everytime. Without wasting hours doing the calculations, this is a very different thing than measuring the percentage of energy required to move a driveshaft over a long period of time as some kind of simple percentage. You really need to do some large complicated calculations to get the real math behind the phenomenon here.

This 44ms difference you noted in your simplified calculations could be comparable to input lag. While 44ms isn't alot, it's certainly noticeable. In competitive FPS, 50ms can make or break you. Using that same super simple math, if you can gain 44ms from just a driveshaft, imagine what you gain from dropping 20lbs from brakes, 10lbs from the flywheel, 28lbs from tires/wheels all of which have a much larger moment of inertia than a driveshaft or pulley. How about another 150lbs from other sprung sources? The effects all compound.

And we are still only talking about moving in a straight line. Lets talk about turning! I look forward to your swept path analysis. We really need to get an auto engineer with some real software to get in here, we are all apparently the wrong kinds of scientists/engineers for this level of discussion. I am anyway, I just deal with electrical engineering in aerospace.

[CBR600RR]

Originally Posted by Koa

He said noticeable difference bro. That, combined with the findings that the ratio for rotational to nonrotational mass is 1.1:1 (I.E no realizable difference when we're looking at 10 pounds, which would mean that 10 pounds taken from the driveshaft equals 11 pounds taken anywhere else)

Sorry bud but you can't argue with physics. Love that you ignore everything in the forum and focus on what you can wrap your mind around

LOOK AGAIN, BUD! I wasn't arguing about whether it would be a "noticeable difference" or not. I was simply stating that is clear-cut-obvious as to which would be the better option to remove weight. I'll quote you again, "you can't argue with physics!" Wrap your mind around that, BRO.

Looks to me that you are "ignoring everything that is in the forum".

[s2d4]

Originally Posted by CBR600RR

LOOK AGAIN, BUD! I wasn't arguing about whether it would be a "noticeable difference" or not. I was simply stating that is clear-cut-obvious as to which would be the better option to remove weight. I'll quote you again, "you can't argue with physics!" Wrap your mind around that, BRO.

Looks to me that you are "ignoring everything that is in the forum".

All this yelling from you makes everything you say much much more awesome.

[CBR600RR]

Originally Posted by s2d4

All this yelling from you makes everything you say much much more awesome.

haha I'm not a fan of being called bro and bud within the same few sentences, so I had to reciprocate.

[zooki]

Thanks guys....😂

[tennisfreak]

I have a suggestion.

How about making your point and then leaving it at that?

I think what puts off some people is the repeated posts in multiple threads about how smart you are and how you can disprove something get tiresome after a while.

The information given is actual good info, useful, and even helpful. You just need to let people decide for themselves whether they want to acknowledge and use it.

Its ok to make a point but to constantly pound into the ground your right and someone else is wrong just eventually pisses people off.

So, regardless of who is right and who is wrong, make your point and let it go. If people want to spend their money on something that others think is a waste it does no good to go into all of the threads telling them they are stupid (maybe not directly but indirectly).

[stugray]

Originally Posted by industrial

I afraid you are still missing the point. You boiled down the difference in energy storage over one continuous acceleration. Nobody is saying you gain lots of horsepower with this mod. Assuming your calculations are correct which I'm not going to double check (but really, thanks for doing) for this debate, you come to the conclusion that the difference in a singular straight line acceleration event is 44ms given a weight of 2800lbs and overall duration of 16.2 seconds.

What you are missing is... That 44ms is nearly completely front loaded. So that difference would be largely the same regardless of if you were testing 0-30, 0-2, 0-150, and even 55-60...anytime you change your rate of acceleration (load an unloaded system). You are overcoming the mass moment of inertia everytime. Without wasting hours doing the calculations, this is a very different thing than measuring the percentage of energy required to move a driveshaft over a long period of time as some kind of simple percentage. You really need to do some large complicated calculations to get the real math behind the phenomenon here.

This 44ms difference you noted in your simplified calculations could be comparable to input lag. While 44ms isn't alot, it's certainly noticeable. In competitive FPS, 50ms can make or break you. Using that same super simple math, if you can gain 44ms from just a driveshaft, imagine what you gain from dropping 20lbs from brakes, 10lbs from the flywheel, 28lbs from tires/wheels all of which have a much larger moment of inertia than a driveshaft or pulley. How about another 150lbs from other sprung sources? The effects all compound.

And we are still only talking about moving in a straight line. Lets talk about turning! I look forward to your swept path analysis. We really need to get an auto engineer with some real software to get in here, we are all apparently the wrong kinds of scientists/engineers for this level of discussion. I am anyway, I just deal with electrical engineering in aerospace.

The calcs above show that (in full on max acceleration - dont care what target speed you are shooting for) the energy consumed by spinning up the driveshaft is ~.25 hp.
And that is making a LOT of simplifications that give the benefit of the doubt to those that think it will be a noticeable difference.
AND you do notice that in the calcs above I am assuming that the drivsshaft reduction in weight was the WHOLE 30 LBS!

In truth if we compensate for all of the other rotating mass and the actual reduction in weight of the driveshaft the difference of the driveshaft is even LESS (probably closer to 1/10 hp).

And YES IF you use timing systems or dataloggers, you WILL see the difference (I never said you wouldnt)

I still stand by my initial statement (that started the shitstorm):

Originally Posted by stugray

Lightened drivetrain components do NOT give "biggest bang for the buck" when it comes to increased acceleration/hp-gains per $$.

If you shed 10 lbs from a driveshaft, you will not feel any difference (in car acceleration) compared to removing the same weight from your spare tire.

And based on my calculations above, this is a fact (unless we believe that someone out there CAN feel less than 1/4 hp difference).

So again I say IF you can feel the difference in the performance of your car with a lightened driveshaft then you can ALSO tell that you are down less than 2 gallons of gas from a full tank. I would bet that no-one on this forum can tell the difference two gallons makes without a datalogger.

[stugray]

And slightly OT:
regarding the "Grimspeed research" you can believe everything you read on the internet right?
These guys appear to be "authorities on Audio technology":
http://www.audioquest.com/ethernet/diamond

Yet they make claims like:

"All insulation slows down the signal on the conductorinside. When insulation is unbiased, it slows down parts of the signaldifferently, a big problem for very time-sensitive multi-octave audio.AudioQuest’s DBS creates a strong, stable electrostatic field which saturatesand polarizes (organizes) the molecules of the insulation."

"DIRECTIONALITY:All audio cables are directional. The correct direction is determined bylistening to every batch of metal conductors used in every AudioQuest audiocable. Arrows are clearly marked on the connectors to ensure superior soundquality. For best results have the arrow pointing in the direction of theflow of music. For example, NAS to Router, Router to Network Player."


But since THEY supposedly know what they are talking about and I am just some shmuck, we should believe them and not me when I say "they are completely full of shit!"

So are they authorities on the technology, or are they just trying to sell you snake oil?

[stugray]

Originally Posted by tennisfreak

I have a suggestion.

How about making your point and then leaving it at that?

I think what puts off some people is the repeated posts in multiple threads about how smart you are and how you can disprove something get tiresome after a while.

The information given is actual good info, useful, and even helpful. You just need to let people decide for themselves whether they want to acknowledge and use it.

Its ok to make a point but to constantly pound into the ground your right and someone else is wrong just eventually pisses people off.

So, regardless of who is right and who is wrong, make your point and let it go. If people want to spend their money on something that others think is a waste it does no good to go into all of the threads telling them they are stupid (maybe not directly but indirectly).

In THIS case I had numerous people chiming in that HAD NOT READ the rest of the thread and were making the same (wrong) claims again & again.

And at least where I work, you can have a room full of engineers all making their own points and apparently yelling at each other and none of them get offended.

It is just the way Engineer's brains work.
If I say something wrong at work, and my co-worker calls "Bullshit" we dont get pissed at each other, we figure out where the error is.

"Normal" people cannot handle being asked questions if they dont know the answer. They get defensive (and pissy)
REAL engineers know how to NOT get offended if they dont know the answer and just say "I dont know, but I'll go do some research and get back to you"

[tennisfreak]

Originally Posted by stugray

And at least where I work, you can have a room full of engineers all making their own points and apparently yelling at each other and none of them get offended.

It is just the way Engineer's brains work.
If I say something wrong at work, and my co-worker calls "Bullshit" we dont get pissed at each other, we figure out where the error is.

"Normal" people cannot handle being asked questions if they dont know the answer. They get defensive (and pissy)
REAL engineers know how to NOT get offended if they dont know the answer and just say "I dont know, but I'll go do some research and get back to you"

I don't disagree with or want to try and disprove any of your statements, I am just trying to keep the peace and notice some people are getting highly upset.

I'm a software developer for a large corporation and we are of a very similar mindset as you.

This forum is not that way though, and as we have seen, some people get very offended.

[industrial]

Originally Posted by stugray

And slightly OT:
regarding the "Grimspeed research" you can believe everything you read on the internet right?
These guys appear to be "authorities on Audio technology":
http://www.audioquest.com/ethernet/diamond

Yet they make claims like:

"All insulation slows down the signal on the conductorinside. When insulation is unbiased, it slows down parts of the signaldifferently, a big problem for very time-sensitive multi-octave audio.AudioQuest’s DBS creates a strong, stable electrostatic field which saturatesand polarizes (organizes) the molecules of the insulation."

"DIRECTIONALITY:All audio cables are directional. The correct direction is determined bylistening to every batch of metal conductors used in every AudioQuest audiocable. Arrows are clearly marked on the connectors to ensure superior soundquality. For best results have the arrow pointing in the direction of theflow of music. For example, NAS to Router, Router to Network Player."


But since THEY supposedly know what they are talking about and I am just some shmuck, we should believe them and not me when I say "they are completely full of shit!"

So are they authorities on the technology, or are they just trying to sell you snake oil?

Let's not get into the world of high end audio. That's a whole different kind of stupid. Grimspeed isn't selling braided silver grounding kits for $5000. I would agree that people should be wary of the marketing "research" presented by companies to sell their product. Which...is another reason to love weight reduction mods. At least we can agree that we aren't hurting anything with this mod which is more than can be said for many "performance" parts found here. You get a 10lb reduction and a stronger shaft with one less point of failure. The performance benefits are irrefutable even if they may also be difficult to quantify. This is not snake oil, not even close. Weight loss as a performance modification is legit and every pound counts. It gets harder with more expense and sacrifice as you go. This mod is easy, cheap and significant in my opinion. Since there is no convincing you otherwise, this seems like a good place to leave the conversation.