aluminum drive shaft - anyone?

[FirestormFRS]

Originally Posted by Pete156

Actually some of the driveshaft's weight is unsprung, is it not?

No.

[tennisfreak]

Some individuals are very committed into entering every single thread about removing weight with lightweight pulleys, shafts, flywheels and letting everyone know they are wasting their money and going to blow their engines.


My pulley set should have blown my engine over 15k miles ago.

[s2d4]

Originally Posted by tennisfreak

Some individuals are very committed into entering every single thread about removing weight with lightweight pulleys, shafts, flywheels and letting everyone know they are wasting their money and going to blow their engines.


My pulley set should have blown my engine over 15k miles ago.

bro science for the win.

[Caspeed]

Originally Posted by Xinshadow

I've had the DSS aluminum unit on my car for about 14 months now. Without getting into any maths, does it make a difference is acceleration feel? Yes, but slight. However in terms of total weight reduction its pretty significant for not a lot of money, and I plan to go with a lightweight flywheel down the road so it made sense.

The biggest change you will see, and I'm surprised no one mentioned this yet, is that it makes heel-toe shifting SIGNIFICANTLY easier, saving some wear and tear on your gearbox over time.

That said you will notice an increase in NVH, with the rubbing noise some others have described, and you may also feel a pulse through the gas pedal when the diff kicks in that the stock shaft kept muted.

Interestingly after going through some winters with both units, the factory one was developing small surface rust spots in a few areas, whereas the aluminum one for obvious reasons still looks fresh as a daisy. I'd be more worried about a factory one becoming unbalanced and damaging the gearbox over time in harsher climates than I would be about the aluminum one doing any harm.

Overall I'd say its a pretty effective cheap mod, if you're willing to work on your driving technique enough to take advantage of it.

Could you please explain to me how a lighter driveshaft can have some effect on heel & toe shifting? If you were talking about a lighter flywheel I would agree. The driveshaft isn't even connected to the engine while doing a heel & toe. Furthermore the driveshaft is rotating at differential speed.

[stugray]

Originally Posted by industrial

I'd just like to point out that the science of physics and the engineers involved in the design of automobiles universally agree that lighter driver shafts are beneficial to performance cars as long as their strength is not compromised. This is hard science. There is no arguement here.

What Stugray is arguing is a completely subjective opinion on whether he thinks a mod is worth it after reading internet articles.

This forum is fucking ridiculous sometimes.

I am also an engineer, so I do have a clue.
And I have repeatedly pointed out the "science" as have others.
I have NEVER said that there is no benefit.

[Caspeed]

Originally Posted by Pete156

Actually some of the driveshaft's weight is unsprung, is it not?

Not in our cars. The driveshaft is connect to the diff which is mounted on the chassis. There is no movement in the driveshaft or diff. If we used a live axle like in most domestic rear wheel drive cars then yes there could be unsprung welght from a driveshaft. But it would be a fraction of it's total weight.

[Pete156]

Originally Posted by Caspeed

Not in our cars. The driveshaft is connect to the diff which is mounted on the chassis. The is no movement in the driveshaft or diff. If we used a live axle like in most domestic rear wheel drive cars then yes there could be unsprung welght from a driveshaft. But it would be a fraction of it's total weight.

Thank you

[D K]

Would you rather lose 5lbs from your flywheel, or 5lbs from a lighter battery?

[s2d4]

Originally Posted by D K

Would you rather lose 5lbs from your flywheel, or 5lbs from a lighter battery?

25lbs from a lighter battery.

[Xinshadow]

Originally Posted by Caspeed

Could you please explain to me how a lighter driveshaft can have some effect on heel & toe shifting? If you were talking about a lighter flywheel I would agree. The driveshaft isn't even connected to the engine while doing a heel & toe. Furthermore the driveshaft is rotating at differential speed.

Sure! When we're first learning to heel toe, its often very abrupt and bucky when the transmission is reengaged since you have to spin up all those driveline components; to really do it right you have to get your rpms into a 200-300 rpm window of where you are matching speed. With lighter driveline components the practical effect is the window for a smooth feeling downshift now widens to about 500-600 RPM. It's not a crazy difference but its very noticeable on the track at higher speeds. Even my HPDE instructor could tell it was there after a lap in the car haha

[stugray]

Originally Posted by Xinshadow

Sure! When we're first learning to heel toe, its often very abrupt and bucky when the transmission is reengaged since you have to spin up all those driveline components;...

You are never "spinning up" all those driveline components when talking about the clutch plate back, because that portion is ALWAYS connected to the road and is spinning at whatever velocity is appropriate for the car's speed.
You can never "feel" the differece of just a couple of pounds in that section of the driveline because it is coupled to the ground and therefore "spinning it up" means accelerating the car.
When accelerating the whole 2500 pound car a couple of pounds of rotational mass is in the noise.

Now if you had the car up in the air and you were spinning up JUST the driveline components (clutch disk, U-joints, driveshafts, CV joints, axles, hubs, rotors, wheels, tires - all that weighs over 100 pounds), could you feel the difference of 15 pounds difference in the driveshaft? I say MAYBE, but probably NOT because it is the one piece of that whole puzzle that contributes the least to the rotational inertia of that part of the system.

Now do the same experiment but take 15 pounds off the tires - you WILL feel the difference because the tires contribute the mostto the rotational inertia of that part of the system.

[Xinshadow]

Originally Posted by stugray

You are never "spinning up" all those driveline components when talking about the clutch plate back, because that portion is ALWAYS connected to the road and is spinning at whatever velocity is appropriate for the car's speed.
You can never "feel" the differece of just a couple of pounds in that section of the driveline because it is coupled to the ground and therefore "spinning it up" means accelerating the car.
When accelerating the whole 2500 pound car a couple of pounds of rotational mass is in the noise.

Now if you had the car up in the air and you were spinning up JUST the driveline components (clutch disk, U-joints, driveshafts, CV joints, axles, hubs, rotors, wheels, tires - all that weighs over 100 pounds), could you feel the difference of 15 pounds difference in the driveshaft? I say MAYBE, but probably NOT because it is the one piece of that whole puzzle that contributes the least to the rotational inertia of that part of the system.

Now do the same experiment but take 15 pounds off the tires - you WILL feel the difference because the tires contribute the mostto the rotational inertia of that part of the system.

My mistake on wording, I probably should have said "makes it easier to match the speeds of" as I'm not talking about accelerating the whole car, merely that the rpm overlap to allow a smooth downshift is widened considerably. I find in my case with everything else going on when circuit driving, having a little extra cushion to hit the sweet spot is great. Mileage will vary by driver of course, and there are other mods to do first for a track toy, but the difference is great enough to be worthwhile for any track toy, regardless of platform.

[stugray]

Originally Posted by Xinshadow

My mistake on wording, I probably should have said "makes it easier to match the speeds of" as I'm not talking about accelerating the whole car, merely that the rpm overlap to allow a smooth downshift is widened considerably.

And this is where changing the rotational inertia of the engine side of the equation will do what you are suggesting.
So a lightened flywheel (or crank/pistons) will make rev transitions easier while reducing the "slam" feel when releasing the clutch.
In fact this is really the only place where you could "feel" the difference of the crank pulley mod.
And where reducing the rotating mass TOO much will make the car less driveable and prone to stalling from a standing start.

The weight of the driveshaft will not help in this situation.

[Caspeed]

Originally Posted by Xinshadow

My mistake on wording, I probably should have said "makes it easier to match the speeds of" as I'm not talking about accelerating the whole car, merely that the rpm overlap to allow a smooth downshift is widened considerably. I find in my case with everything else going on when circuit driving, having a little extra cushion to hit the sweet spot is great. Mileage will vary by driver of course, and there are other mods to do first for a track toy, but the difference is great enough to be worthwhile for any track toy, regardless of platform.

The ony time a lighter driveshaft will have any effect on shifting is if your car has a driveshaft between the clutch and the tranny. Think Porsche 928.

Double clutching matches the speed of the input shaft with the next gear on the output shaft, which is turning at diff speed. That is all.

Reducing rotational mass is generally a good thing. But remember that it's effect is determined by it's moment of inertia. The further from the center of rotation the greater the effect. 5Lbs from a wheel/tire assembly will be greater in it's effect (not even counting unsprung weight) than 5Lbs on a driveshaft.