aluminum drive shaft - anyone?

[Koa]

Originally Posted by Turdinator

Anybody want to take bets on how long before this thread is locked? Anybody?

I hope it gets locked.. the butthurt is strong in people who can't understand the worth of sound math and logic

[Manic]

The thing is though, people defending the magical properties of light weight drive shafts are essentially just arguing that they can feel a perceivable difference over stock. The math alone proves that to be false. Now they're resorting to marketing claims and anecdotal evidence.

Basically, they spent money on a part and they want to believe that it was the best bang for their buck. I would have to imagine that they're the same people who proclaimed up and down that aftermarket intake kits produced SUBSTANTIAL differences over stock or even over an aftermarket air filter.

It all just stems from the inability to be satisfied with their own purchases. They need everyone else to agree with their butt dyno claims because then they'll feel validated each time they drop the big bucks on their car.

Have y'all tried lightweight seat belt tensioners? They have CF ones that reduce the seat belt pulley weight upwards of 80%. You can really feel the difference in belting speed after you install them.

[Captain Snooze]

Originally Posted by industrial

CFRP propeller shaft.

The new BMW M3 Sedan and new BMW M4 Coupe also feature a CFRP propeller shaft. CFRP’s high rigidity and low weight mean that the drive shaft can be produced as a single-piece component without a centre bearing. This provides 40 per cent weight savings over the previous model, and the reduction in rotating masses results in sharper throttle response. The use of carbon in these models is a reminder that BMW is a global leader in high-strength, lightweight CFRP construction, and that it was BMW who brought out the first mass-production vehicle with a body consisting entirely of this material – the innovative BMW i3.

One has to remember this was released by the marketing department. Their job is to create desire and justify the product. Owners of this car can tell their friends, and themselves, that is a great performance part. BMW also likes sprouting how 50/50 weight distribution is optimal as well.

Disclosure. I have a cf drive shaft. Am I pleased with it? Yes, and that's all that matters. But then again, my battery cost me close to AUD$1100.

[Hawk77FT]

Originally Posted by Koa

I hope it gets locked.. the butthurt is strong in people who can't understand the worth of sound math and logic

Interestingly enough, you seem to be the one that has gone a bit crazy buddy! People tried to have a reasonable conversation (engineering, maths and all that) but you came along like a crazy One direction fan calling people names because they dont want to accept the mathematical results.
As someone here explained, there are few things that you cannot ignore: this debate is much more complex than you or I can wrap their heads around. A software would be able to measure the benefits of it and by the looks of it, there is no doubt about it (BMW and few other car makers are doing it now, regardless of their marketing stuff).
Grimmspeed TESTED their product and reported back the results. They are engineers specialized in such area. I would trust them rather than someone that tries to convince vehemently that he is right disregarding the fact that (and i will say it again) this is a more complex problem than one can resolve.
There are plenty of cars out there that mathematically (on paper) they look great but they are shit to drive, so the stuff on paper should be taken with a grain of salt! (Ex VW GTI vs R32 0 huge difference on paper, not so big on the track).

By the looks of it, this has become more of who's got better insults or who's got more followers.
As someone else said: test the car with and without it. I have and I felt a difference. Huge difference? No! Noticeable ? Yes.
Add few more things in the mix: wheels, brakes, etc...and you will get even more. Is like arguing whether an intake makes a difference or not. (it does, but you need few other things to make that "difference" more noticeable.

I would be grateful if we could keep this convo civilized with no names calling and stuff! You are not making your point more believable by doing that..just sayin'!

[Captain Snooze]

Originally Posted by Manic

The thing is though, people defending the magical properties of light weight drive shafts are essentially just arguing that they can feel a perceivable difference over stock. The math alone proves that to be false........
It all just stems from the inability to be satisfied with their own purchases. They need everyone else to agree with their butt dyno claims because then they'll feel validated each time they drop the big bucks on their car.

Sure, I agree with the sentiment but I think it is somewhat of a self supporting circle. Noob jumps on forum "What's best bang for my buck?" and 50 replies tell him/her that a light weight crankshaft pulley will reduce 0-100 mph by 5 seconds. So noob fits lwcp and low and behold, he can feel the difference because everyone has told him so.

It is fact (well, I think it's a fact but I could be wrong lol) that the gray stuff upstairs is not rational and is subject to self deception. It is the way things are.

[Dimman]

It doesn't matter if you win by an inch or by 44 milliseconds.

Winning's winning.

[TheVoiceOfReason]

Originally Posted by Captain Snooze

Sure, I agree with the sentiment but I think it is somewhat of a self supporting circle. Noob jumps on forum "What's best bang for my buck?" and 50 replies tell him/her that a light weight crankshaft pulley will reduce 0-100 mph by 5 seconds. So noob fits lwcp and low and behold, he can feel the difference because everyone has told him so.

It is fact (well, I think it's a fact but I could be wrong lol) that the gray stuff upstairs is not rational and is subject to self deception. It is the way things are.

Confirmation Bias
[ame="http://en.wikipedia.org/wiki/Confirmation_bias"]Confirmation bias - Wikipedia, the free encyclopedia[/ame]


I also think increased NVH makes people percieve far larger gains than they actually have.

[Captain Snooze]

Originally Posted by TheVoiceOfReason

I also think increased NVH makes people percieve far larger gains than they actually have.

Yeah, the good ol' "I have a loud exhaust so now I am faster" syndrome.

[Poodles]

Originally Posted by Koa

I edited to say brake upgrades.. you could piece together a used setup (sti?) for around 600-800... buuuut that probably does not ensure quality and YMMV on that one haha

The aluminum driveshafts are super cool, don't get me wrong.. would love to have one, even if it tricks my butt dyno and gives me that much more peace of mind that my severely underpowered engine won't ever twist it (jokes, stu, jokes, don't call that out!)

but they are awesome. Especially if you want to go big, big power, it makes a lot of sense

One piece driveshaft doesn't make sense for big power as big power = higher speeds.


One can easily go over the critical speed of a one piece driveshaft in this car because of it's low final drive!

Originally Posted by industrial

How do you prove with hard science that something does not produce an effect that is noticeable? It's pure speculation on how someone may perceive the difference based on "internet science". I don't care if someone claims to be an engineer here, you can say anything you want. The way he acts strikes me as more of a typical reddit kid that can look stuff up rather than someone who actually works in science or knows anything about the most basic tenants of science. I mean, if the absolutely ridiculous analogies he comes up isn't a glaring example to his real level of knowledge I don't know what is.

One word: Placebo

Originally Posted by industrial

There really is no real way to dumb down the physics here. It's complex. It should be enough to know that losing 10 pounds for $400 might be worth it as is. The fact that it's also rotational weight absolutely makes a positive impact. How can we quantify this? It's hard. It's hard to quantify how exactly a lot of things work but we can explain it qualitatively. Why does one person get to force his theoretical qualitative opinion down everyone's throat? That's fucking ridiculous. Go tell people that black taillight housings suck because your opinion as someone who doesn't own a black taillight is parroted by other car forum sheeple. This is a car hobby. None of it really makes sense. This is for fun.

It's not hard for him and math and science is not opinion.

Originally Posted by industrial

Someone in this thread is basically saying...based on articles he's read, he doesn't think we should feel what we are feeling. People can physically taste the difference between 2 identical liquids based on the label on the outside. We are that susceptible to our brain overriding our senses. If installing a driveshaft really does make someone feel their car is faster, who the fuck are you to say otherwise?

It's making it LESS safe as it's introducing a critical speed failure mode into the equation.

Originally Posted by Turdinator

I suspect the "noticeable difference" comes from more than just weight reduction. My guess is the lack of centre bearing and other things to control NVH built into the stock drive shaft make for a more direct feeling of power delivery.

I believe @stugray that the weight reduction will have a negligible effect on the car but @Dimman has a good point, it is not up to Stu how people spend their money and he should know that arguing with people on the internet is a waste of his intellect. Make your case and move on whether people believe it or not. The right people will read it and learn from it. This is a forum, I could start a thread about the sky being blue and someone somewhere would argue with me.

As I've already said, the center bearing is NOT for NVH, but for safety to raise the driveshaft's critical speed.

Originally Posted by stugray

In this case (simple inertia dyno) the only things that are measured are Drum RPM, and time.
Using those two numbers (drum angular velocity) and elapsed time (∆t), you can derive the power.
Power is the rate of doing work.
The work done is the change in rotational energy of the drum.
If you start from a stop, w = 0 so rotational kinetic energy is zero
The power is the final kinetic energy of the drum (in joules) divided by the time it took to spin the drum to the final speed.
So rotational kinetic energy is E = 1/2*I*w^2 ( where E is in joules, I is drum rotational Inertia in kg-m^2, and w is angular velocity in radians/second).

So total energy is: (Efinal - Estart)/time-to-reach-Efinal (in seconds).
This will give an average "Joules per second" which is the definition of Watts.

Note: this will only give you average power over the whole "pull" and will not provide the nice dyno charts we typically see which represent instantaneous power across the RPM range.
This precisely how I calclulated an average hp draw of spinning just the driveshaft.

for the driveshaft example:
Rotational inertia of the 30 lb driveshaft (@3 inch diameter) is : 0.01974 kg.m^2
wstart = 0 RPM, wfinal = 5600 RPM
5600 RPM = 35185.8 radians per minute = 586 radians per second
The energy stored in the driveshaft = E = 1/2 * .01974*586^2 = 3389 joules

If it took 16.2 seconds to spin the driveshaft from zero to 5600 RPM, then the 3389 joules were spread out over 16.2 seconds so the power (energy per unit time) is: 3389 joules/16.2 seconds = 209.2 watts.

209 watts = .28 horsepower.


Side note: So since the headlights consume more than 200 watts, I would argue that driving with your headlights off vs On, would make more of a difference than removing the entire 30 pounds from the driveshaft (NOT accounting for the reduction in overall vehicle weight). SO I am sure to start whole new flurry of naysayers with that one.....

So to be clear which of the following experiments would make the bigger difference:

Replace the stock driveshaft with a 15 pound lighter one (shed 15 pounds from vehicle weight AND 15 lbs from rotational mass at the driveshaft) and do a 1/4 mile run with the headlights ON
AND
Remove 15 pounds from the spare tire (shed 15 pounds of vehicle weight) and do a 1/4 mile run with the headlights OFF.

Which run is faster?
The one where you removed the weight from the spare tire, and drove with headlights off.

Well, if it's a BRZ you're only consuming 35w x 2, but that's the headlights only, but you still make a good point

Originally Posted by industrial

Can't seem to step away since this insanity keeps going.

Can you please tell me why you are absolutely fixated on 0-100mph acceleration test? Of all the tests to try and prove your opinion that is the best test (0-120mph would be better or better yet, a standing mile?) Who is talking about drag racing here except everyone that is trying to say driveshafts aren't a good mod for drag racing? Are we seriously still having this discussion? What you are doing is akin to determining the worth of an aerodynamic aid based on drag at 15mph. It just doesn't make sense. Sure your numbers aren't wrong but you are making the wrong comparison. Please tell me why you aren't seeking to disprove your own hypothesis before rattling off these inane examples? It's seriously annoying. You are myotically fixated on this singular example and that is horrible science.

All these false choices you present are ridiculous too. Why can't someone remove the spare, turn off their headlights and have a lighter driveshaft? Do you go into every exhaust thread and tell people they are wasting their money, that mathematically, a turbo kit is the only way to go? $1000 for 5-10whp or $4000 for 100whp? Easy! Science! Drive on a cold day and make more power than that $300 intake. Science! One nerd to rule them all! Nanu nanu!

1) 0-100MPH is published and he's done all his previous calculations with the same metric. Changing that metric would only confuse people.


2) Turbos have lag (which is quantifiable) and they void warranties meaning they can possibly be more expensive in the long run...

Originally Posted by jsimon7777

Well, you guys could just test it, ya know. Here's one way that cuts out most user error:
Put the car on stands, or at least raise the rear wheels. Go into first and rev to six thousand. Get your stopwatch ready. Now lift quickly while starting the timer. Click it off when the engine hits 1000rpm. Then install the new drive shaft. Repeat the process. Do them both in the same conditions and oil temperatures. You could also do it in different gears.

Whatever way carries more mass will carry more momentum to defeat the friction and therefore will spin longer. I'd wonder if the drive shaft shop job is stronger. They claim up to 800hp. I've no idea what the stock shaft can handle. However, i did notice that the AL shaft is 3" and the stock is about 2 5/8.

Axial strength is pretty pointless on a driveshaft. I'll say it again: DRIVESHAFT CRITICAL SPEED IS FAR WORSE.

Originally Posted by industrial

If what you say was truly the case, why does almost every single high performance front engine, rear wheel drive car have an aluminum or carbon fiber driveshaft? RX8, 350z, 370z, GTR, zo6, db8, amgs, bmw m cars, ETC ETC ETC ETC?

Maybe you should go tell all the OEMs they are wasting their time.

RX8: Kinda carbon fiber (carbon reinforced plastic)
350Z: carbon fiber
370Z: same fing car...
GTR: Carbon fiber.
Z06: Doesn't count as it's a torque tube setup (tranny is in the rear)


Most of those are carbon fiber. Carbon fiber is used because it allows them to run a single piece driveshaft without having driveshaft critical speed issues. It's also fragile and has to have shields to prevent foreign objects from hitting it.

Originally Posted by Koa

Driveshaft strength

He's said it again and again.. the overwhelming benefit of upgrading to a DSS or equiv. part is driveshaft strength over stock. The DSS shafts are a realized and noticable upgrade in that department hands down.

You've listed vehicles with significantly higher price points and power outputs (sans RX8), and subsequently are more inclined to offer this peace of mind.

You can continue to ignore sound math and perspectives, though, to make yourself feel better

I don't see anyone breaking the stock driveshaft. It's also NOT stronger as (god I feel like I'm beating a dead horse here) driveshaft critical speeds will occur.


As none of the driveshaft companies want to give out their specs of the shaft (big surprise as it's probably unsafe), I'm guessing at the specs.


If someone wants to get me length, diameter, and wall thickness, it's easy to figure this stuff out...

[Koa]

Originally Posted by Hawk77FT

Interestingly enough, you seem to be the one that has gone a bit crazy buddy! People tried to have a reasonable conversation (engineering, maths and all that) but you came along like a crazy One direction fan calling people names because they dont want to accept the mathematical results.
As someone here explained, there are few things that you cannot ignore: this debate is much more complex than you or I can wrap their heads around. A software would be able to measure the benefits of it and by the looks of it, there is no doubt about it (BMW and few other car makers are doing it now, regardless of their marketing stuff).
Grimmspeed TESTED their product and reported back the results. They are engineers specialized in such area. I would trust them rather than someone that tries to convince vehemently that he is right disregarding the fact that (and i will say it again) this is a more complex problem than one can resolve.
There are plenty of cars out there that mathematically (on paper) they look great but they are shit to drive, so the stuff on paper should be taken with a grain of salt! (Ex VW GTI vs R32 0 huge difference on paper, not so big on the track).

By the looks of it, this has become more of who's got better insults or who's got more followers.
As someone else said: test the car with and without it. I have and I felt a difference. Huge difference? No! Noticeable ? Yes.
Add few more things in the mix: wheels, brakes, etc...and you will get even more. Is like arguing whether an intake makes a difference or not. (it does, but you need few other things to make that "difference" more noticeable.

I would be grateful if we could keep this convo civilized with no names calling and stuff! You are not making your point more believable by doing that..just sayin'!

Okay brother you're just sayin has been noted.

It's not outside of our heads and expertise to wrap our brains around this, though. It's not rocket science. We don't have to throw up our hands and say, "WELL, TOO HARD TO UNDERSTAND HERE!" and try to hide behind that. Physics is a VERY well understood and applied science. The logic and math check out. Let me ask you... what do you think?

[Dimman]

My buddy had a CF driveshaft grenade on him. Wasn't pretty. Not sure but we think it was from a bad fit between the CF tube and metal yoke part covered by too much adhesive.

Ever since then I've been a bit leery of half-engineered driveshafts. Learning that the harmonic stuff is weird, aluminum's fatigue properties, and how welding it adds stress risers while removing initial heat treat strength has been enough for me to get uncomfortable looking at a few aluminum DS in the past.

Are these things you're interested in discussing, Stu (in your inside voice)?

[industrial]

Originally Posted by Captain Snooze

One has to remember this was released by the marketing department. Their job is to create desire and justify the product. Owners of this car can tell their friends, and themselves, that is a great performance part. BMW also likes sprouting how 50/50 weight distribution is optimal as well.

Disclosure. I have a cf drive shaft. Am I pleased with it? Yes, and that's all that matters. But then again, my battery cost me close to AUD$1100.

Yes but if there wasn't a real performance benefit, it wouldn't exist on the OEM level in such ubiquity. Most OEMs would just pass the savings (from a steel driveshaft over megabucks cf) on to profits. I find it hard to believe that any OEM would go to any length to spend more money on the driveshaft for marketing. It's under the car and over the exhaust. The customer will never see it or feel the difference (because a steel one was never installed). Also, just because you can't trust the marketing department at Audioquest cables doesn't mean you can't trust all corporate sources.

This discussion is beyond futile here. There are countless books and sources that say reducing rotating mass (to include the driveshaft) is beneficial for a performance car. Almost every OEM does this. There are aftermarket driveshafts available for almost every performance car foreign and domestic, that doesn't come with one. It's not like lightweight driveshafts are something new that came along with the ft86. People in other car communities pay 2-5x more for lighter and more exotic driveshafts.

Since we are beyond the polite stage, all the math in this thread is nearly worthless for this discussion. As I've said over and over, you need modeling software specific to this application that the OEMs have to demonstrate mathematically whether this mod is "worth it". I'm not sure why these few guys are so vehemently defending their position that this mod is not "worth it" since none of them have any real world experience with this mod. Don't know why I'm still here.

[industrial]

Originally Posted by Koa

Okay brother you're just sayin has been noted.

It's not outside of our heads and expertise to wrap our brains around this, though. It's not rocket science. We don't have to throw up our hands and say, "WELL, TOO HARD TO UNDERSTAND HERE!" and try to hide behind that. Physics is a VERY well understood and applied science. The logic and math check out. Let me ask you... what do you think?

Actually, it is complex. Here is an excellent write up which demonstrates the lengths necessary to disprove or prove the point you guys are making. Please don't skim the article and fixate on a sentence and quote it here. Just read it.

http://www.stockcarracing.com/techar..._reducing_moi/

[Manic]

Originally Posted by industrial

There are countless books and sources that say reducing rotating mass (to include the driveshaft) is beneficial for a performance car. .

I'm starting to get the feeling that your computer might have some sort of autoblock feature, setup to block certain words or phrases.

No one has disputed the fact that reducing rotating mass, including the driveshaft, isn't beneficial. The only argument being made by the heretics who believe in math and science is that the benefit of a light weight drive shaft is negligible in the practical scope of the car.

It's akin to taking a heavy shit and driving your car naked in hopes that the reduced sprung weight is going to improve your lap times. Technically you've reduced the sprung weight of your car. Does it have a practical benefit? Nope.

If the OP wants to buy a light weight drive shaft, good on him. But stop trying to convince yourself that you've purchased a miracle drive line upgrade which'll make you .05 seconds faster in the corners. It just won't.