F8X M3/M4 CF Drive shaft mod

[0-60motorsports]

For those interested in SMG fit.






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Nice! Did you modify one already?

[SliM3]

For those interested in SMG fit.






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[Obioban]

Still working on this. Should have it done next week hopefully. Been busy the last week with the baby being born but should have some updates soon and testing to see if the CF driveshaft offers improvement over stock.

Baby was born a week ago and you still haven’t gotten this done?

lazy.

[0-60motorsports]

Still working on this. Should have it done next week hopefully. Been busy the last week with the baby being born but should have some updates soon and testing to see if the CF driveshaft offers improvement over stock.

Congrats bro!! God bless you and the Family.

[Cronenberged]

Still working on this. Should have it done next week hopefully. Been busy the last week with the baby being born but should have some updates soon and testing to see if the CF driveshaft offers improvement over stock.

Enjoy your new born we'll live no rush

[EthanolTurbo]

Still working on this. Should have it done next week hopefully. Been busy the last week with the baby being born but should have some updates soon and testing to see if the CF driveshaft offers improvement over stock.

[Slonik]

how is it on the F8x cars with this driveshaft when it comes to install/removal? do they also have to loosen diff? or is the F8x DS flange adjustable/telescoping to allow install/removal with out touching the diff

f8x driveshaft has telescopic coupling near the front flange (you can see rubber boot on pics), and better to save it during conversion.

[Altaran]

I wonder if it might be viable to make the shaft a tiny bit shorter when cutting the flanges, to allow the expanding/contracting portion to cover the install without diff removal. I have no idea how much wiggle room there is in that joint.

If I recall correctly it should be 12mm movement.

Though the wiggle room is needed to account for engine/tranny movement. Unless of course you run solid mounts...

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[George Hill]

185mph is the top of the speedo = same shaft RPM as the F8X. To me, this is sufficient.

Only if the rear gear, transmission gear and tire size are the same.

Not sure if it matters, but BMW thought it did so that is why I asked.

I will eventually do some standing mile events and other high speed stuff so while this is likely only relevant to a small group of people I figured it was still worth asking since we are here discussing the mod to begin with.

[Obioban]

I should have been more specific... and yes it is 7600 so the delta isn't nearly as big knowing that. 6th gear at redline is going to be the fastest driveshaft RPM, however realistic it is to get there.

S55 - 7600 RPM with .872 = 8,715rpm
S54 - 8000 RPM with .828 = 9,661rpm
*S54 - 7216 RPM with .828 = 8,715rpm

10% faster... maybe it doesn't matter, just curious



My car at 7216rpm is 185mph (not factoring any drag) so probably not something I am going to achieve anytime soon or for an extended period of time, but I do have thoughts of going 200 in it so.... lol

(S55 at 7000 RPM is the same driveshaft speed at 170mph in my car which is certainly attainable)

I rarely go past the top of 4th anymore, and have never gone past the top of 5th.

185mph is the top of the speedo = same shaft RPM as the F8X. To me, this is sufficient.

[George Hill]

I assume they meant RPM of the driveshaft, not the engine.

I should have been more specific... and yes it is 7600 so the delta isn't nearly as big knowing that. 6th gear at redline is going to be the fastest driveshaft RPM, however realistic it is to get there.

S55 - 7600 RPM with .872 = 8,715rpm
S54 - 8000 RPM with .828 = 9,661rpm
*S54 - 7216 RPM with .828 = 8,715rpm

10% faster... maybe it doesn't matter, just curious

I think it is 7600 and typically manufacturers over engineer parts to go beyond the stated limit. I'd be more concerned about the torque rating and fortunately, the S55 has plenty of torque.

Then again, BMW did recall some of them as they can fail spectacularly, probably due to that 406 ft/lbs of torque and a defect -

My car at 7216rpm is 185mph (not factoring any drag) so probably not something I am going to achieve anytime soon or for an extended period of time, but I do have thoughts of going 200 in it so.... lol

(S55 at 7000 RPM is the same driveshaft speed at 170mph in my car which is certainly attainable)

[Slideways]

In the BMW video, they state the CF diameter is directly related to max RPM, which IIRC is 7k on an S55.

Any thoughts on how this relates to spinning the S54 8k+?

I think it is 7600 and typically manufacturers over engineer parts to go beyond the stated limit. I'd be more concerned about the torque rating and fortunately, the S55 has plenty of torque.

Then again, BMW did recall some of them as they can fail spectacularly, probably due to that 406 ft/lbs of torque and a defect -

[Obioban]

In the BMW video, they state the CF diameter is directly related to max RPM, which IIRC is 7k on an S55.

Any thoughts on how this relates to spinning the S54 8k+?

I assume they meant RPM of the driveshaft, not the engine.

[slavik1988]

how is it on the F8x cars with this driveshaft when it comes to install/removal? do they also have to loosen diff? or is the F8x DS flange adjustable/telescoping to allow install/removal with out touching the diff

The YFCM is telescopic as well. In my opinion it is inherent in its 1 piece design. The factory shaft can be bent out at the CSB.

[George Hill]

In the BMW video, they state the CF diameter is directly related to max RPM, which IIRC is 7k on an S55.

Any thoughts on how this relates to spinning the S54 8k+?