aluminum drive shaft - anyone?

[cdrazic93]

That a very vague question. More information is needed to give you an accurate critical speed value.

[juliog]

Relevant chart, different car but illustrative nonetheless:


Source:
http://www.jameshakewill.com/clutch-size.pdf

[stugray]

Originally Posted by juliog

Relevant chart, different car but illustrative nonetheless:


Source:
http://www.jameshakewill.com/clutch-size.pdf

THANKS! That is an excellent piece of information.
This is exactly why many of us said that reducing the Flywheel mass will make a noticeable difference, but a pulley or driveshaft is in the noise.
That graph shows just how far in the noise those components are.
In the case of the LW-crank pulley, it is probably less than 1% of the entire drivetrain rotating mass.
See how the drivetrain losses are almost imperceptible in that graph? What do we think you would see if you plotted JUST the Crank Pulley? - You would see NOTHING!
Same goes for the driveshaft.

[tennisfreak]

You want more acceleration?

Change final drive ratio. Better than lightweight anything x100.

[nunonuna]

Originally Posted by stugray

What do we think you would see if you plotted JUST the Crank Pulley? - You would see NOTHING!
Same goes for the driveshaft.

Even both mods shows nothing gain LOL~ Only difference I can tell is better rev match feel after LWCP when I down shift or heel & toe.
Oh and around 15lbs weight saving from both parts.

[churchx]

Pulleys do less then flywheel simply because they weight less and you can gain less by lightening them vs lightening much heavier in stock flywheel (which is of bigger diameter at that with more mass further from center). Driveshaft might gain less simply because it's after gearbox and rotates at slower speeds and is of smaller diameter vs FW, as energy to spin up something depends not from mass only, but also from how far that mass is from rotating center and rotating speeds you need it spin up to.
I am not completely sure if it's same for our cars as for F-1600 though. Different mass, different airdrag, different power, different gearbox/drivetrain. For example are losses in sport sequential gearbox same as in normal ones designed for quitness/less power? Drive shaft probably also is a bit of different length/mass in car with both engine and driven wheels in rear, then in classic RWD like twins. Hence comparing oranges to apples?

[Jaden]

Originally Posted by stugray

THANKS! That is an excellent piece of information.
This is exactly why many of us said that reducing the Flywheel mass will make a noticeable difference, but a pulley or driveshaft is in the noise.
That graph shows just how far in the noise those components are.
In the case of the LW-crank pulley, it is probably less than 1% of the entire drivetrain rotating mass.
See how the drivetrain losses are almost imperceptible in that graph? What do we think you would see if you plotted JUST the Crank Pulley? - You would see NOTHING!
Same goes for the driveshaft.

I'm not claiming that there is a perceptible difference, but using this graph in the way you are is not accurate.

You would need a graph detailing ONLY the losses. This graph shows where all of the hp goes. Most of it goes to acceleration. So drivetrain being a small percentage of where ALL hp goes is not valid in supporting your argument.

It looks like drivetrain is closer to 13-15% of total losses most of which are probably in the diff, but 2-3% of total losses wouldn't be out of the realm of possibility especially in the 60 foot, not the .01% that you are claiming.

Jaden

p.s. And that is JUST considering drivetrain losses, on top of that, you have the reduced weight for the overall car.

[stugray]

Originally Posted by Jaden

I'm not claiming that there is a perceptible difference, but using this graph in the way you are is not accurate.

You would need a graph detailing ONLY the losses. This graph shows where all of the hp goes. Most of it goes to acceleration. So drivetrain being a small percentage of where ALL hp goes is not valid in supporting your argument.

It looks like drivetrain is closer to 13-15% of total losses most of which are probably in the diff, but 2-3% of total losses wouldn't be out of the realm of possibility especially in the 60 foot, not the .01% that you are claiming.

Jaden

I do not follow all of your statement above.
However: In the graph I see that at the point where the drivetrain has the highest percentage of losses is ~1.75 hp at the 50 meter point which is 1.75/110 = 1.6% of the total HP. (Flywheel is accounted for separately)
While over the majority of the range it is far less than that.

And remember - In a steady state HP measurement the rotating mass consumes ZERO percentage of the total HP measured.
The total "losses" in the drivetrain are due to friction and has nothing to do with the mass of the rotating assembly.

[Jaden]

Originally Posted by stugray

I do not follow all of your statement above.
However: In the graph I see that at the point where the drivetrain has the highest percentage of losses is ~1.75 hp at the 50 meter point which is 1.75/110 = 1.6% of the total HP. (Flywheel is accounted for separately)
While over the majority of the range it is far less than that.

And remember - In a steady state HP measurement the rotating mass consumes ZERO percentage of the total HP measured.
The total "losses" in the drivetrain are due to friction and has nothing to do with the mass of the rotating assembly.

I understand that drivetrain consumes zero in a steady state. Almost all performance driving is NOT in a steady state though. I don't see many people dragging, or going around a track at a steady 5000 rpms.

With all that being said, I would be doing it with only cumulative weight reduction in mind. I'll replace it to reduce the weight, along with all other weight reduction that I can do.

Jaden

[JDKane527]

Originally Posted by churchx

Pulleys do less then flywheel simply because they weight less and you can gain less by lightening them vs lightening much heavier in stock flywheel (which is of bigger diameter at that with more mass further from center). Driveshaft might gain less simply because it's after gearbox and rotates at slower speeds and is of smaller diameter vs FW, as energy to spin up something depends not from mass only, but also from how far that mass is from rotating center and rotating speeds you need it spin up to.

Definitely agree. The Kinetic Energy affects how much inertia the rotating assembly has. Decreasing overall inertia has benefits.
Angular kinetic energy is defined:
KE = (1/2)*(Iw^2)
I = moment of inertia
w = angular velocity

The faster a mass is rotating, the more effect it has on impacting Kinetic Energy. The crank pulley and flywheel are rotating at the same angular velocity. The flywheel would make a substantially larger impact than the crack pulley would make.

KE = (1/2)*(Iw^2)
I,flywheel >> I,crankpulley

The alternator pulley is rotating much faster than the crank pulley due to the pulley diameter. It could be argued that lightening the mass of the alternator would have more of a benefit than lightening the water pump pulley as the water pump pulley diameter is similar to the crank pulley diameter. It could also be argued that lightening the alternator may or may not cause harmonics/resonances in the engine as the rotating mass has been altered.

KE = (1/2)*(Iw^2)
w,alternator >> w,crankpulley

The case of the driveshaft, I is altered while velocity remains constant before and after.
KE = (1/2)*(Iw^2)
I,carbon << I,steel

I = mr^2
As m,carbon ~= (0.5) m,steel
Correct me if I'm wrong, but I hear the radius is slightly less for the carbon driveshaft.
r,carbon ~= (0.99) r,steel
I,carbon = (0.5)(0.99^2) I,steel
I,carbon = (0.4905) I,steel

KE,carbon = (0.4905) KE,steel

It would help for angular acceleration of the assembly slightly and for braking, but would not have as large of an impact as lightening a component with a higher angular velocity.

[Poodles]

Originally Posted by GT86_PRAGUE

In what speed will DSS CF MT going to brake?

Without knowing the specs on it (length, inside and outside diameter of the tube), I can't comment. As a general rule, if you're going with CF, you're probably fine so far as critical speeds go, but CF is less durable for a street driven car.


99% of the arguments about pulleys, driveshafts, and wheels on this forum (and the internet in general) wouldn't happen if people understood what "moment of inertia" was...

[GT86_PRAGUE]

So, from real world:
How much will this thing improve car acceleration?
5%?
50%?

[churchx]

I recall reading mention in few posts by what time drag runs or track time was shortened by lightening mods .. but am too lazy to search for those. I don't even recall if those posts were in threads related to these aftermarket parts, or in some build or racing related threads. Hard to choose right search terms to dig them up, remembering only fact that lightening actually work.

[stugray]

Originally Posted by GT86_PRAGUE

So, from real world:
How much will this thing improve car acceleration?
5%?
50%?

From page 5 -

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!