aluminum drive shaft - anyone?

[industrial]

Originally Posted by Koa

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.

Wow, it's like talking to a bowl of soggy cereal. Goodbye cereal.

[Koa]

Originally Posted by industrial

Wow, it's like talking to a bowl of soggy cereal. Goodbye cereal.

poor guy, hope you learn to learn someday

[wootwoot]

No mine is bigger!

[stugray]

Originally Posted by industrial

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?)

Umm maybe because 0-100 MPH times are published, and simple. I could have used 31.4159 MPH would that have made you feel better?
Oh.... and becasue the results would be the same! Spinning up the driveshaft consumes .28 horsepower regardless of what top speed you are shooting for! (as long as we are at max acceleration)

Originally Posted by industrial

Who is talking about drag racing here except everyone that is trying to say driveshafts aren't a good mod for drag racing?

The only time I mentioned "drag racing" was in response to the person who was talking about burnouts and (incorrectly) about sprung vs unsprung weight.

Originally Posted by industrial

Are we seriously still having this discussion?

Well... you are as well. What does that mean?

Originally Posted by industrial

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.

Ok, so 0-100 MPH acceleration is a "inane" example?
Hmm... that's pretty much a standard metric in ALL performance automobile evaluations. I guess all those engineers who evaluate cars are stupid too.

Originally Posted by industrial

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.

Why didnt YOU try to disprove these ramblings before posting them (might have saved you some typing).
WHY would I first start out to disprove a FACT? when I KNOW it to be a fact?
WHY dont YOU try to prove that the moon doesnt exist?

Originally Posted by industrial

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!

You are seriously disturbed.
Instead of comparing removing 15 lbs from the driveshaft to removing 15 pounds from someplace like.... the spare tire (something MOST of us do at the track ANYWAY!)

I guess now I'll go compare shedding 15 pounds from the driveshaft to removing two pink flamingos from my yard.

WHAT THE FUCK ARE YOU TALKING ABOUT?!?!
Actually after typing all of this, it is clear that you are just trolling to get in on the action. Jealous? Need a hug?

[EAGLE5]

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.

[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.

[Sypher]

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 you explain why it takes 16.2 seconds to get to 5600RPM? (at work and dont have time to figure it out lol)

[Koa]

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.

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

[industrial]

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

https://m-power.com/_open/b/closedro...d=3021&lang=en

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.

[Koa]

LOL YOU'RE QUOTING BMW'S MARKETING DIRECTLY HAHAHAHAHAAHAHH

Such a troll...

[stugray]

Originally Posted by Sypher

can you explain why it takes 16.2 seconds to get to 5600RPM? (at work and dont have time to figure it out lol)

16.2 seconds is the published 0-100 MPH time for the BRZ.
Since we are talking about the driveshaft not the engine (a fact missed by some on this thread), it is coupled to the ground via the final drive gear & the wheels. It doesnt spin up & down or ever get "uncoupled" from the wheels.
When the car accelerates the driveshaft goes from 0 RPM to ~5560 RPM when the car hits ~100 MPH. (numbers werent meant to be exact)
Again, the only reason I picked 0-100 MPH is that it is a standard metric and is a published #.

[Wayno]

Honestly, don't you smart arses have anything better to do? If you have so much free time, go do auto-x, skidpan or just drive your car 0-60mph, install one, repeat, then come back and tell us you can't notice the difference. Then go buy one of those yank V8's and drive it with 2 throttle positions. Don't waste people's time with irrelevant 100mph calculations. This is the next best thing after lighter wheels.

[Koa]

Originally Posted by Wayno

Honestly, don't you smart arses have anything better to do? If you have so much free time, go do auto-x, skidpan or just drive your car 0-60mph, install one, repeat, then come back and tell us you can't notice the difference. Then go buy one of those yank V8's and drive it with 2 throttle positions. Don't waste people's time with irrelevant 100mph calculations. This is the next best thing after lighter wheels.

LOL

You aussies and your nationalist profiling.. Yank v8s.. what does that even mean

Did you even bother reading the evidence and math here?

Just saying, this is NOT the next best thing after lighter wheels if you're looking for weight reduction. What's your basis for saying this? A lightweight battery would yield better results for FAR less money. Sorry bud.. math and logic prevails here.

[Turdinator]

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