CF driveshaft?

[5erman]

Was wondering-
1.What is the m3 driveshaft made out of-assuming normal steel but maybe not?

2.Anyone sell a CF shaft for the m? Would be good for 20 Hp or so loss in parasitic drag compared to a steel and not to mention a really nice increase in rev speed to redline which is important for these cars to get up to higher rpms?

[ManAndMachine]

Not sure what the stocker is made of but ACPT does make carbon driveshafts..

http://www.acpt.com/driveshaft/index.html

[Erhan]

That would be massively expensive. It has to cope with quite a bit of torque.

[UNNATRAL]

I want one!

[ManAndMachine]

Originally Posted by erhanh

That would be massively expensive. It has to cope with quite a bit of torque.

Agree..I believe the ACPT was track tested and approved up to 800HP

[5erman]

well CF is a lot stronger than steel which we probalby have, so really a more imortant factor is making sure its well balanced and drives like stock. True CF is going to be strong so thats not an issue.

I think people drop too much money on other mods in search of power (not a sC or stroker obviously) but lightweight CF drive shaft and some light weight wheels would probalby give you an equivelent of 40 more hp due to decrease parastic losses.

I would buy one

[Erhan]

Yes CF is stronger, but I believe its strenght is based on the wave pattern. And in a drive shaft, there is a rotational force, right? So I don't think you can sit and make some CF tube to use as a drive shaft. It has to be well engineered with proper CAD tools. Also, this is not a cosmetic part like a roof or bumper. It has to stand the engine force in every single mile, even in idle. Not to mention track days.

Engineering a part like this, using an expensive material and production combined with low volume will make it very expensive. With all due respect, a stupid CF diffuser costs 1500$. That's a lot of money.

[5erman]

Originally Posted by erhanh

Yes CF is stronger, but I believe its strenght is based on the wave pattern. And in a drive shaft, there is a rotational force, right? So I don't think you can sit and make some CF tube to use as a drive shaft. It has to be well engineered with proper CAD tools. Also, this is not a cosmetic part like a roof or bumper. It has to stand the engine force in every single mile, even in idle. Not to mention track days.

Engineering a part like this, using an expensive material and production combined with low volume will make it very expensive. With all due respect, a stupid CF diffuser costs 1500$. That's a lot of money.

well obviously bro-but as the link showed the companies that make these are often dedicated drive shaft companies and they are not making cheap japanese rear wings out of cheap CF. It is prob a 1500-2000 dollar part compared to what I see on the net for other cars with this mod.

I would get it if it was more readily available.

[Erhan]

If it is 2000$, I'd buy (well, not now, due to warranty stuff). As you said, it'll give more gain than many other mods. But as I said, a CF rear diffuser is 1500$, CF mirror cups are $600... There is a huge markup in these things.

Maybe we should ask these guys how much they'd charge, if they'd do a group buy deal etc?

[sensi09]

Was checking prices on the acpt driveshaft for the STI and it costs around $1200.

BTW, there are some less expensive cars like the 350z/370z which get a CF or CF composite driveshaft from the factory.

[Erhan]

Well, I believe it'll cost $1200 for the STI. But this an M3.. We have to pay the "sucker" markup, that's my problem.

[Brosef]

although it's a rotating part, it's so narrow in diameter that the gains (or reduction in losses, to be accurate) from reducing rotating inertia would likely be a lot less than you might expect. It's worth weighing the stock driveshaft and doing the simple math to see if the gains are compelling.

[5erman]

Originally Posted by Brosef

although it's a rotating part, it's so narrow in diameter that the gains (or reduction in losses, to be accurate) from reducing rotating inertia would likely be a lot less than you might expect. It's worth weighing the stock driveshaft and doing the simple math to see if the gains are compelling.

Its not necessarily the overall diameter that matters. When looking at the wheels for example, the outher portion has a much higher moment of inertia than the center and thus weight savings on the outher portion is a lot better.

However the driveshaft is indeed a small diameter but that just means the moment of inertia is consistent with mass saved anywhere in the shaft. The small diameter itself does not meanit has a low moment of inertia, its just that typically the "outer" portion of a diameter is the highest and not the center. In this one the center and outside is pretty much the "same thing"

anyway I am not an expert and dont know the exact gains but its probably one of those mods that even if a dyno didnt show much, the real world performance would be strong in really getting the motor revvin much faster.

[Brosef]

Originally Posted by 5erman

Its not necessarily the overall diameter that matters. When looking at the wheels for example, the outher portion has a much higher moment of inertia than the center and thus weight savings on the outher portion is a lot better.

However the driveshaft is indeed a small diameter but that just means the moment of inertia is consistent with mass saved anywhere in the shaft. The small diameter itself does not meanit has a low moment of inertia, its just that typically the "outer" portion of a diameter is the highest and not the center. In this one the center and outside is pretty much the "same thing"

anyway I am not an expert and dont know the exact gains but its probably one of those mods that even if a dyno didnt show much, the real world performance would be strong in really getting the motor revvin much faster.

I disagree. And the fact that the mass of the driveshaft is confined to a small diameter was exactly my point. even if you assume that all of its mass is on the outside of the shaft, it's still gonna be minimal.

You also proved your ignorance by saying that the CF drive shaft would "get the motor revvin much faster."

[Malek@MRF]

Will you gain top end hp? Yes.

Will you lose a ton of low end torque? Yes.

CF driveshafts should remain off street cars that spend majority of their time on the street. Unless your winding your car past 5500 rpm at all times, then go for it!

The carbon composite propeller shafts that Nissan claims to use are no where near as light as a true Carbon Fiber unit.

[zhangzeyuandss]

Originally Posted by Malekreza11

The carbon composite propeller shafts that Nissan claims to use are no where near as light as a true Carbon Fiber unit.

+1. Used to be a Z owner. confirmed on this.

[Littlekeel]

Originally Posted by Malekreza11

Will you gain top end hp? Yes.

Will you lose a ton of low end torque? Yes.

CF driveshafts should remain off street cars that spend majority of their time on the street. Unless your winding your car past 5500 rpm at all times, then go for it!

The carbon composite propeller shafts that Nissan claims to use are no where near as light as a true Carbon Fiber unit.

Curious to why you think you would lose a ton of low end torque?

[Malek@MRF]

Originally Posted by Littlekeel

Curious to why you think you would lose a ton of low end torque?

Basic laws of physics.

Lighter flywheels, lighter internals, lighter driveshafts, all cause a loss of low end torque at the wheels. Obviously there would be no loss of BHP with lighter propeller shafts, but the power goes through the wheels at the end of the day.

Anytime you take away some of the rotational mass out of the units that propel the wheels, you will have a loss of torque, or at times a shift in the torque band to the right (still meaning, a loss of low end torque).

[Brosef]

Originally Posted by Malekreza11

Basic laws of physics.

Lighter flywheels, lighter internals, lighter driveshafts, all cause a loss of low end torque at the wheels. Obviously there would be no loss of BHP with lighter propeller shafts, but the power goes through the wheels at the end of the day.

Anytime you take away some of the rotational mass out of the units that propel the wheels, you will have a loss of torque, or at times a shift in the torque band to the right (still meaning, a loss of low end torque).

that is 100% incorrect.

[Malek@MRF]

Umm ok. It's provable data.

Horsepower and response will increase at a cost of shifting the torque band to the right.

[Littlekeel]

Just thinking about this for a bit.

T = I*Alpha

T = torque
I = moment of inertia
Alpha = angular acceleration

Assuming the driveshaft is a thin walled cylinder, then the inertia will be equal to M*R^2, where M is the mass of the driveshaft and R is the radius.

The engine is assumed to develop the same torque whether it is connected to the driveshaft or not.

The only variable changing in the equation would be I, the moment of inertia.

As inertia decreases due to mass decreasing and torque values remaining constant, alpha will increase. The shaft will turn at a faster rate, but the torque being applied to it will be the same no matter how you look at it.

I don't see where the torque output will be a loss?

[MaxL]

Originally Posted by Malekreza11

Basic laws of physics.

Lighter flywheels, lighter internals, lighter driveshafts, all cause a loss of low end torque at the wheels. Obviously there would be no loss of BHP with lighter propeller shafts, but the power goes through the wheels at the end of the day.

Anytime you take away some of the rotational mass out of the units that propel the wheels, you will have a loss of torque, or at times a shift in the torque band to the right (still meaning, a loss of low end torque).

Any formulas to show how this works? Does not make sense to me how the torque would go up at high RPM and go down at low RPM from change of mass. Would be good to see the formula at least for determining what RPM is "high" and what is "low" (so essentially the critical point).