Performance & Modding Experts - ALU/Carbon Driveshafts - Whats the score?

Gibbo · 29 Jun 2006 at 22:55

Hi there

Do a lot of reading and research on the US forums regarding Mustangs etc. etc.

One of the quite common mods over there is swapping out the 2-piece drive shaft for an ALU/Carbon single piece driveshaft. They are supposedly half the weight, something like 40lbs lighter I think.

They supposedly help the engine rev easier and sites in the US selling them in the US for $600 claim approx 10-15 RWHP more. But this could just be marketing hype as lots of mods claim good gains but in reality give nowhere near the manufacturers claims wheras on other hands some modifications do.

Now I am asking over here as I suppose this is a modification you could make to any car. So is a lighter driveshaft a good modification, does it yield good results especially if your shaving something like 15-20kg off?

For more info see this:-
ALU/Carbon Driveshafts

penski · 29 Jun 2006 at 22:59

American 'tuning advice' unfortunately often leaves a lot to be desired.

It will give you another inch or so on your StangWang at owners club meets but, to be blunt, you'd probably never notice the difference day-to-day.

*n

penski · 29 Jun 2006 at 23:00

Oh...And it's a propshaft, not a driveshaft

Damn 'merkins...

*n

kaiowas · 29 Jun 2006 at 23:09

For starters there's no way that such a change can give you any* more actual power at the wheels. It can however give the same effect as a power increase in terms of acceleration (although it won't affect top speed)

*except maybe minimal immeasurable changes in drivetrain losses that are due to changes in design details rather than the weight saving that I'm not even going to bother discussing.

Wayn0r · 29 Jun 2006 at 23:10

carbon - stronger, lighter, quieter as it absorbs harmonics better without the long term fatigue that can be associated with alu/steel.

A lower rotational mass means you could see gains in whp upto 5% etc.

Cost a lot but id say these days its a very good product to use for getting the power down.

merlin · 29 Jun 2006 at 23:12

Assuming they're quite pricey - I'd want to see dyno proof of the atw gains because I'm struggling to see how it could reduce transmission losses.

Firestar_3x · 29 Jun 2006 at 23:14

Best it could do imho is improve pickup since it will spin up easier, much like a lightened flywheel, at a guess?

NickK · 29 Jun 2006 at 23:14

350Z has a carbon driveshaft. The result is quite a snatchy take on the clutch compared to the non-carbon M3.

merlin · 29 Jun 2006 at 23:14

Firestar_3x said:
Best it could do imho is improve pickup since it will spin up easier, much like a lightened flywheel, at a guess?

^

Wayn0r · 29 Jun 2006 at 23:18

Firestar_3x said:
Best it could do imho is improve pickup since it will spin up easier, much like a lightened flywheel, at a guess?

yea, lightened clutchs, flywheels. There wouldnt be a market for these items if they were no use/

Clarkey · 29 Jun 2006 at 23:19

NickK said:
350Z has a carbon driveshaft. The result is quite a snatchy take on the clutch compared to the non-carbon M3.

can hardly compare the clutch on 2 totally different cars can we now?

The reason the 350z has a carbon prop is for crash safety, the carbon will crush in a heavy collision. This is at least what the designer of it said in an interview with Best motoring.

Gibbo · 29 Jun 2006 at 23:19

merlin said:
Assuming they're quite pricey - I'd want to see dyno proof of the atw gains because I'm struggling to see how it could reduce transmission losses.

Same here m8!

Hence why I'd thought I ask as it seems not many in the US seem to go for this mod. Probably because they all know its maybe pretty pointless unless you are running stupid amount of power like 600+

Probably for myself who will never hit over 500 its probably pointless, just save the cash towards the supercharger.

Wayn0r · 29 Jun 2006 at 23:20

Clarkey said:
can hardly compare the clutch on 2 totally different cars can we now?

The reason the 350z has a carbon prop is for crash safety, the carbon will crush in a heavy collision. This is at least what the designer of it said in an interview with Best motoring.

lol. and you believe that?

kaiowas · 29 Jun 2006 at 23:22

Wayn0r said:
yea, lightened clutchs, flywheels. There wouldnt be a market for these items if they were no use/

They're certainly of use. In terms of increasing acceleration reducing rotating mass from the drivetrain is many times more beneficial than removing mass from elsewhere in the car (for biggest gains you want to remove mass from the fastest spinning components so anything before the gearbox is especially good). It's just that it's somewhat false to claim power gains for such mods in the same way that you wouldn't claim a power gain if you removed your interior.

Firestar_3x · 29 Jun 2006 at 23:23

Wayn0r said:
lol. and you believe that?

Race-developed features such as the carbon-fibre prop shaft (as in Nissan's R390 Le Mans car) not only save weight and reduce inertia, but absorb energy more efficiently in an impact.

Seems to be for everything, which sounds about right

Edit on topic still but from nissan.

The carbon fibre propeller shaft - lighter than steel but stronger - soaks up less power. So you can shift gears more easily. And enjoy more of what the engine produces.

Hmm kinda missleading way of putting it imho.

Gibbo · 29 Jun 2006 at 23:28

kaiowas said:
They're certainly of use. In terms of increasing acceleration reducing rotating mass from the drivetrain is many times more beneficial than removing mass from elsewhere in the car (for biggest gains you want to remove mass from the fastest spinning components so anything before the gearbox is especially good). It's just that it's somewhat false to claim power gains for such mods in the same way that you wouldn't claim a power gain if you removed your interior.

So things like Underdrive Pulleys, lightweight flywheels and lightweight shafts all help the engine rev faster/easier but don't necessary add power but do make things quicker?

My car already has Underdrive pulleys to make it rev easier. Clutch flywheel is STD and I aint changing that as its something I cannot do. But the shaft would cost approx £400 shipped landed in the UK and is something I could fit myself I reckon.

Will it improve my car or is it mostly marketing BS?

Clarkey · 29 Jun 2006 at 23:31

Wayn0r said:
lol. and you believe that?

why on earth would I not believe what the designer has to say about it?

Firestar_3x · 29 Jun 2006 at 23:33

Gibbo said:
Will it improve my car or is it mostly marketing BS?

Acceleration = Force divided by Mass

For a given force, a 'lighter' car will accelerate at a greater rate. "To go faster you make the car 'lighter'."
It takes Force to change the rate at which something is rotating in the same way it takes Force to change the speed an object is moving in a straight line.
As an example: if you remove 10kg mass from a Seven, say, the spare wheel and carrier, the car will be 2% lighter and thus, 2% quicker to accelerate. For example, the 0-60 time will decrease from 5.0 sec to 4.9 secs. That's optimistic for several reasons, but serves to illustrate the point.
The same 10 kg mass could be removed from the engine flywheel and it would have the same effect on the car being accelerated in a straight line as removing the spare wheel and carrier as above. But an addition affect would be that there is less mass for the engine to accelerate rotationally.
The flywheel gets spun from 1000rpm to 7000rpm, back down to 5000 and up to 7000rpm again every time you change up through the gears. Now consider a playground 'roundabout' where you push on it to get it going and the kids love it (quite old fashioned - not seen one for a few years). It takes several seconds of hard pushing to get it up to speed, and yet it's not actually going anywhere - it only has ROTATIONAL velocity and hence only rotational inertia. (Inertia is: "The opposition a body offers to a change in motion." A property of all bodies. Inertia is a 'quality', but measured in terms of mass, which is a quantity).
A 'lighter' equivalent, e.g. a spinning top, is easy to spin-up to speed because it has less mass. So back to our flywheel. I worked out once (long day at work) that from a normal to a lightened flywheel, saving about 3kg, would also give a 0.1 sec advantage 0-60. So I've lost a third of the mass, but got the same effect while accelerating the car in a straight line.
Magical other benefits are that I can change gear more quickly as the engine can drop from 7000 to 5000rpm quicker to let me get into 2nd to give it more "Welly" earlier. So I gain a bit more there.

Here's the science bit....... A concept necessary to predict the behaviour of a rotating mass is that of its "Moment of Inertia". This quantity not only expresses the amount of mass but also its distribution about the axis of rotation. Basically this takes into account that the weight on the edge has more effect than that near the middle. To demonstrate this principle; sit on your office chair, spin it round with your arms and legs straight out. Now pull them all in - you speed-up. Your "moment of inertia" went down as you had less mass away from the centre so you HAVE to rotate faster to keep your (angular) momentum the same.

CONCLUSION: Reducing a given rotating mass (wheels, tyres, engine flywheel, clutch pressure plate, gearbox, prop shaft, differential, drive shafts, wheel hubs and brake discs) is more beneficial to Se7en acceleration in a straight line than reducing the same 'fixed' mass. Reducing a given mass from the periphery of a rotating mass is more beneficial than the same mass removed from nearer the axis of rotation.

Dave Hooper

Personally for 400 notes it seems a little on the steep side but it will make the engine more free revving, but if its the diff between you getting the now or later then i would say no, otherwise yes, unless your 400 can bet better spent on something else (similar price).

Meridian · 29 Jun 2006 at 23:34

Only person I know with one is a guy from the Essex Scooby Crew - he has one on his 460bhp WR1. The work was done by Roger Clark Motorsport IIRC. He like it. but 10-15bhp? I would think that unlikely.

M

Matt82 · 29 Jun 2006 at 23:36

my uncle had an extremely light weight flywheel fitted to his M3. idled a touch rough afterwards but the increase in urge was definately noticable.

simple physics apply. a heavy object requires more energy input to move it. an extreme example would be be opening and closing a cupboard door compared to opening/closing a vault door.

i would do it if they are cheap enough