F8X M3/M4 CF Drive shaft mod

[Bry5on]

Ooh that cutaway picture is great. Can estimate wall thickness pretty well with that. Now we just need someone to cut open a stock driveshaft and measure the wall thickness at all its different diameters

If you have a driveshaft out I can ultrasonically measure thickness without cutting anything

[heinzboehmer]

Found some pretty good info from bmw blog:
http://www.bmwblog.com/2021/04/09/vi...bmw-m3-and-m4/

The guts:


Video from the linked blog post:
https://www.youtube.com/watch?v=gVqHSron50U

At 1:00 in the engineer mentions f8x carbon driveshaft is 90mm heinzboehmer

Ooh that cutaway picture is great. Can estimate wall thickness pretty well with that. Now we just need someone to cut open a stock driveshaft and measure the wall thickness at all its different diameters

[Bry5on]

Found some pretty good info from bmw blog:
http://www.bmwblog.com/2021/04/09/vi...bmw-m3-and-m4/

The guts:


Video from the linked blog post:
https://www.youtube.com/watch?v=gVqHSron50U

At 1:00 in the engineer mentions f8x carbon driveshaft is 90mm heinzboehmer

Clever, I wonder what adhesive is used that’s able to be removed. That might also be useful on our driveshaft and half shaft CV splines..

[meowth]

Found some pretty good info from bmw blog:
http://www.bmwblog.com/2021/04/09/vi...bmw-m3-and-m4/

The guts:


Video from the linked blog post:
https://www.youtube.com/watch?v=gVqHSron50U

At 1:00 in the engineer mentions f8x carbon driveshaft is 90mm heinzboehmer

[heinzboehmer]

Carbon has the extra benefit of stiffness and more inherent damping. The reasons I’m interested in this are for those two and an inertial reduction to help with the clunk when shifting. Would love feedback from anyone who’s done a back to back on those metrics. Seems worth a shot!

Yeah those things definitely make this mod appealing. But still waiting on radii measurements to see if there will be any actual inertial reduction

[Bry5on]

I'll add to.

Just thinking out loud here, but any adverse side effects to the rest of the drivetrain? I.e., increasing the stiffness of the driveshaft potentially impacts XYZ because...

What about NVH? Increase, decrease, or no change?

*Should* be a reduction in harshness on abrupt throttle changes and shifting. Vibration will increase if the balance wasn’t good, and it is a bit harder to balance the longer shaft, although the stiffer/lighter carbon helps mitigate this. Otherwise, I’d estimate no noticeable impact to NVH.

[bimmerfan08]

Carbon has the extra benefit of stiffness and more inherent damping. The reasons I’m interested in this are for those two and an inertial reduction to help with the clunk when shifting. Would love feedback from anyone who’s done a back to back on those metrics. Seems worth a shot!

I'll add to.

Just thinking out loud here, but any adverse side effects to the rest of the drivetrain? I.e., increasing the stiffness of the driveshaft potentially impacts XYZ because...

What about NVH? Increase, decrease, or no change?

[Bry5on]

Carbon has the extra benefit of stiffness and more inherent damping. The reasons I’m interested in this are for those two and an inertial reduction to help with the clunk when shifting. Would love feedback from anyone who’s done a back to back on those metrics. Seems worth a shot!

[Obioban]

its a nice advantage (and it is true for this piece).

i only wanted to draw attention to the weight figures and warn people not getting overexpectations with this piece, cause i'm sure most people expect weight reduction due to the "aerospace material" usage .

my own opinion, that for looking as an upgrade for this piece, i'd prefer to get 6-6.5 kg weight over 8.5kg standard. in this case, it could named as an upgrade (i would be happy with less than 6kg weight, but okay, i'm realistic ). and i'd think twice to do this mod, if weight loss will be up to 1kg.

My recollection from Altaran‘a post was that the e46m and f8x shafts where pretty similar weights stock, but, once you put the lighter e46 flanges on the cf shaft, the weight difference was a couple lbs. Not the case?

[0-60motorsports]

its a nice advantage (and it is true for this piece).

i only wanted to draw attention to the weight figures and warn people not getting overexpectations with this piece, cause i'm sure most people expect weight reduction due to the "aerospace material" usage .

my own opinion, that for looking as an upgrade for this piece, i'd prefer to get 6-6.5 kg weight over 8.5kg standard. in this case, it could named as an upgrade (i would be happy with less than 6kg weight, but okay, i'm realistic ). and i'd think twice to do this mod, if weight loss will be up to 1kg.

Yes, Agreed. Thanks for posting what you already did a year back. Shame the RX8 CF DS did not work out.

[Slonik]

I don't care if its heavier i just want to get rid of the CSB

its a nice advantage (and it is true for this piece).

i only wanted to draw attention to the weight figures and warn people not getting overexpectations with this piece, cause i'm sure most people expect weight reduction due to the "aerospace material" usage .

my own opinion, that for looking as an upgrade for this piece, i'd prefer to get 6-6.5 kg weight over 8.5kg standard. in this case, it could named as an upgrade (i would be happy with less than 6kg weight, but okay, i'm realistic ). and i'd think twice to do this mod, if weight loss will be up to 1kg.

[0-60motorsports]

I can do that. I have access to a lot of these so should be able to push out 10-20 for the community if necessary.

I predict each one should cost somewhere been $600-900 depending on whether you need new flanges, fresh CV joint etc.

Sounds reasonable, if you can do the SMG one at the lower end of the cost spectrum im game. Thanks for doing this when and if you do.

[0-60motorsports]

I dont care if its heavier i just want to get rid of the CSB

[fattycharged]

Glad I scrolled through entire thread

[Slonik]

its a nice mod for e8x e9x M cars, but i'm not sure about e46m3. first of them has quite heavy driveshaft, and e46 doesn't (compared to CF from f8x).
I'm a little bit further, than just theory, cause i've made an attempt in last season .
before writing about my experience, i'll add some figures:
e46m3 driveshaft weight (with cv joint) - 8.5kg (18.7lbs)
e9x m3 driveshaft weight (with cv joint) - 13.1kg (28.9lbs)

F8x cf driveshaft (with joint also, but different type, looks lighter) - 7.6kg (16.7lbs)

year ago i had brand new f8x driveshaft on hands and after some thoughts and measurements (too tight fitment with f8x tube, due to the huge diameter, compared to the stock shaft) i've decided to try with rx8 cf driveshaft for my conversion, instead of f8x. rx8 driveshaft has smaller diameter tube, so obviously, more weight loss potential over f8x driveshaft. yep, i had some doubts, cause rx8 has no torque, compared to our cars, but anyway, for NA engine i decided that it could be enough.
so i've made it, but unfortunately, i saw some issues (growing hum/noise on 220+kmh speeds) during first rides and i had a trackdays too close and i made a decision not to risk and fit my old driveshaft for the race. and after that, i didn't tried it again and didn't tried to solve or to identify an issue. maybe in this season i will have a chance for second attempt.

i'll post the pics of my result for better visibility, but for some attentive guys i'll make a remark - i had dct swapped car, so my driveshaft little bit shorter than standard one and has different front flange (e46 driveshaft was cut on the front end and new end was welded).

but for the side by side comparison i think its quite good.
my e46m3 dct converted driveshaft:

150g lighter, than stock e46m3.
8360g (18.4lbs)


converted with rx8 cf driveshaft
6070g (13.4lbs)



so if i've got little bit more than 2kg drop on rx8 driveshaft, i don't think that you can get anything less than 7.5kg on f8x, maybe even heavier.


and in this case i think there is not a lot sense to make this conversion. but anyway, up to you.