aluminum drive shaft - anyone?

[Koa]

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".

uhh noo.. considering you haven't realized that with rotating mass vs sprung mass is a 1.1:1 ratio, some claiming 1.26:1 ratio... here's the takeaway: it literally does NOT make a difference.

Your "point" doesn't hold any water because it DOES NOT make a single difference. It's people like you who try to come here and make a "point" just for the sake of making a point. What is it you're really arguing? "clear cut obvious"- uhh no, it's clear cut obvious that your point sucks. Lol get used to it when you have that kind of mindset.

Refer to Razic's very eloquently stated and explained post about how you're so god damn wrong it hurts that you're still here >> http://www.ft86club.com/forums/showp...6&postcount=93

Try again

[Koa]

P.S. .... @CBR600RR ... nice taste in bikes at least. If I didn't pick up my '05 r6 for $2,000 with no fairings and a broken right clipon, I woulda went honda.

[stugray]

Originally Posted by 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.

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.

[s2d4]

I wonder why people get all defensive and hurt over being wrong, it's like the best thing ever since you won't make the same mistake again.

[Koa]

Originally Posted by s2d4

I wonder why people get all defensive and hurt over being wrong, it's like the best thing ever since you won't make the same mistake again.

It's uncomfortable acknowledging that we're not all-knowledgeable, especially after we've committed to a position or decision. I'll be forward and say I never knew rotating mass and sprung mass were so close to each other ratio-wise, placement variables considered.

As Karl Seguin put it, "Learning is more important than Knowing"

http://openmymind.net/2012/4/18/Lear...-Than-Knowing/

I follow that mantra with a zeal in all I do, both professionally as an accountant, passionately as a gearhead and musician, and personally as a lover and friend. It's all about knowing (pun intended) how to learn

[Manic]

ITT: Lightweight driveshaft owners struggle to justify their $300+ purchases.

[Captain Snooze]

@stugray
Thank you for a detailed explanation.

[joe strummer]

Originally Posted by Captain Snooze

@stugray
Thank you for a detailed explanation.

From me too. Very interesting/educational stuff.

[industrial]

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.

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!

[Koa]

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!

All I read is, "mad mad mad mad mad mad"

[industrial]

Originally Posted by Koa

All I read is, "mad mad mad mad mad mad"

U BETRA SHUT UR MOUF OR IM KICK UR AZZ. OMG SO MAD RITE NOW. IM MMA FIGHTER I WILL MES U UP!!!!111111!!!!! :mad0 260:

Seriously? What are we 12?

[Koa]

Originally Posted by industrial

U BETRA SHUT UR MOUF OR IM KICK UR AZZ. OMG SO MAD RITE NOW. IM MMA FIGHTER I WILL MES U UP!!!!111111!!!!! :mad0 260:

Seriously? What are we 12?

I just don't get it.. Stu and zaric laid out in VERY solid math and logic why claims of this driveshaft reporting back any noticeable improvement to lap times/power is a pretty much closed case example of butt dyno trickery more than anything.

At the end of the day, the rotational weight savings does MINISCULE amounts of gain over the equivalent sprung amount... soooo much so, that realistically, no appreciable gain in lap time or performance to, in their opinion, warrant the $400 spent.

Notice the bold is where the facts stop and opinion starts. How aligned one is to that opinion is open to debate. In my opinion, that $400 can be used for MUCH better purposes, if on a budget. If a dude(tte) really is looking to spent more money on his car, and already has a full header system/tune/brakes/whatever... fuck. go for it!

but if he/she does and comes here to try and exclaim how amazing it is, and how they can definitely tell, etc... don't expect the people who understand the real forces at work to hold their tongue.

[industrial]

Originally Posted by Koa

I just don't get it.. Stu and zaric laid out in VERY solid math and logic why claims of this driveshaft reporting back any noticeable improvement to lap times/power is a pretty much closed case example of butt dyno trickery more than anything.

At the end of the day, the rotational weight savings does MINISCULE amounts of gain over the equivalent sprung amount... soooo much so, that realistically, no appreciable gain in lap time or performance to, in their opinion, warrant the $400 spent.

Notice the bold is where the facts stop and opinion starts. How aligned one is to that opinion is open to debate. In my opinion, that $400 can be used for MUCH better purposes, if on a budget. If a dude(tte) really is looking to spent more money on his car, and already has a full header system/tune/brakes/whatever... fuck. go for it!

but if he/she does and comes here to try and exclaim how amazing it is, and how they can definitely tell, etc... don't expect the people who understand the real forces at work to hold their tongue.

Lap times? What lap times? It was all theory and the math while correct was applied only enough to prove a point which is: A lighter driveshaft does not make a humanly noticeable difference in overall 0-100 times. No argument here, as far as I know, nobody else said otherwise. But people would be hard pressed to notice a difference between 92 vs 93 octane on a 0-100 run. Or a 5 degree temperature change. Or 2 psi change in tires. Or a 2mm change in tire width. Do none of these things matter as well?


To prove or disprove whether a driveshaft makes a tangible difference in responsiveness and ability to change directions at speed is an infinitely more difficult problem which hasn't been addressed by anyone mathematically. (because it's really hard without dedicated software)

[Koa]

Originally Posted by industrial

Lap times? What lap times? It was all theory and the math while correct was applied only enough to prove a point which is: A lighter driveshaft does not make a humanly noticeable difference in overall 0-100 times. Well neither would 92 vs 93 octane. Or a 5 degree temperature change. Or 2 psi change in tires. Or a 2mm change in tire width.

No argument here, as far as I know, nobody else said otherwise.

To prove or disprove whether a driveshaft makes a tangible difference in responsiveness and ability to change directions at speed is an infinitely more difficult problem which hasn't been addressed by anyone mathematically. (because it's really hard without dedicated software)

Stu addressed this mathematically.. very eloquently. Tangible difference from lowering the driveshaft's weight from 30lbs stock to ZERO is the same as turning off one's headlamps for the straights. So what does 10 pounds reduction do to the system?

We could discern real quick that such a miniscule variable wouldn't have a compounded, noticeable effect on the track. It's a no brainer once we combine Stu and Zardic's mathematical logic with the fact that DSS and other driveshaft companies fail to put any real world data out that backs up any claim for performance increases they may have.