Group Buy: YFCM Carbon Driveshafts

[Epoustouflant]

Good morning NAM3 gents,

Following up on this thread, I've created a separate thread to launch this group buy. The E46 M3 application of the YFCM Carbon Driveshafts are included in the 2023 Winter Group Buy for all BMW M applications.

To participate in the Group Buy, it's here. If you don't yet have an account, it's free! Register here.

• 25% off MSRP
• 3-4 months lead time
• We need to hit 30x across M applications, we are currently at 17x within 24 hours.
• Payment in full once we reach 30x. Refundable anytime.

Specifications and benefits:
The main benefits of the carbon driveshaft are entirely derived from the 1 piece, stiffer design over stock 2 piece.

Every clutch operations and throttle inputs are tighter, smoother, faster.

In short: it's lighter and stronger than steel, vibration free, and is backed by a 1 year replacement warranty. It will never unglue due to the proprietary self-locking flange patented by M. Lee at YFCM.

To learn more about the E46 M3 specifications, it's here.

The quick backstory:
A limited group of Connex members got the E46 M3 driveshaft in the Fall last year as early adopters. I've had mine installed last Summer to validate specs.

I've documented my experience with the E46 specific driveshaft in a Special Series on my Build Journal here.

1. Demystification of carbon driveshafts. Link.
   1. Unboxing impressions and review of technical features.
2. The I6 installation procedures. Link.
   1. The preliminary checks, while you're-in-theres, the recommended hardware, the installation notes and final validation specs.
3. Got my 420G feeling like a Springfield. Link.
   1. My driving impressions based on my experience with BMW M manuals, along with Ryan's in-depth road & track review with a comparaison to the VAC driveshaft.

The new 6spd flange:
YFCM has since continued development specific to the 6spd tranmission to reduce cost, and weight. It has a new shorter flange.

[Obioban]

In! Exciting! 😁

It's seriously been way too many years of not having a viable CF driveshaft for this platform. This looks to be the one that finally checks all the boxes, without compromise.

[Advorsor]

In

[heinzboehmer]

I see mentions of the carbon driveshaft diameter being bigger than the steel one here: https://euroconnex.co/blogs/build-jo...aft-procedures

Do you how much the increase is? Moment of inertia of a cylinder goes up proportionally to the square of radius, so small increase there could negate the decrease in weight. I'm just curious if this piece will lower moment of inertia of the rotating bits in the drivetrain.

[4getr34]

This is awesome. Was there any test notes for SMG?

[Bry5on]

I see mentions of the carbon driveshaft diameter being bigger than the steel one here: https://euroconnex.co/blogs/build-jo...aft-procedures

Do you how much the increase is? Moment of inertia of a cylinder goes up proportionally to the square of radius, so small increase there could negate the decrease in weight. I'm just curious if this piece will lower moment of inertia of the rotating bits in the drivetrain.

Area moment is actually to the 4th power of diameter/radius. If the OEM driveshaft is 19lb at 3” OD, an 11lb driveshaft must be <3.4” OD to have a reduction in area moment (the thing that lets it spin up/down faster). Some assumptions here obviously, which would generally favor the OEM setup at these weights.

Area moment is not the only benefit (overall 8lb savings, plus some torsional stiffness increase, presumably) but I’d have thought that to be a primary motivator for a carbon driveshaft.

edit: still think this is a cool product, to be clear! 8lb of mass is still 8lb, even if there isn’t a rotating weight/inertial benefit.

edit2: My above 4th power statement is incorrect. Heinz is right that it’s to the square - remember folks, always go back to units!

[Epoustouflant]

I see mentions of the carbon driveshaft diameter being bigger than the steel one here: https://euroconnex.co/blogs/build-jo...aft-procedures

Do you how much the increase is? Moment of inertia of a cylinder goes up proportionally to the square of radius, so small increase there could negate the decrease in weight. I'm just curious if this piece will lower moment of inertia of the rotating bits in the drivetrain.

I can compare - it's not a lot.

This is the former V3 I tested that didn't work at all from another brand.

This is awesome. Was there any test notes for SMG?

Not specifically to the E46, but on my V10, yes - it's here and here.

[heinzboehmer]

Area moment is actually to the 4th power of diameter/radius. If the OEM driveshaft is 19lb at 3” OD, an 11lb driveshaft must be <3.4” OD to have a reduction in area moment (the thing that lets it spin up/down faster). Some assumptions here obviously, which would generally favor the OEM setup at these weights.

Area moment is not the only benefit (overall 8lb savings, plus some torsional stiffness increase, presumably) but I’d have thought that to be a primary motivator for a carbon driveshaft.

edit: still think this is a cool product, to be clear! 8lb of mass is still 8lb, even if there isn’t a rotating weight/inertial benefit.

Hmm, I thought area moment was mostly relevant to quantify torsion and the mass moment tells you how resistant a body is to changes in rotational velocity. Might need to brush up on things.

Anyway, I also assumed this was the primary motivator for this driveshaft, which is why I asked. Agreed though, this seems like a cool product.

[simonnim]

Does this bolt up to a SMG -> manual conversion? They're the same tranny aren't they?

[Epoustouflant]

Anyway, I also assumed this was the primary motivator for this driveshaft, which is why I asked. Agreed though, this seems like a cool product.

It's common misconception. I've talked about this in my E9x M3 review here.

We conflate weight reduction with rotational inertia.

Many often misunderstand carbon driveshafts: I did too!

We expect them to feel like lightweight flywheels: we are used to these drastically improving low to mid range engine response.

While the driveshaft does lose 10+ lbs over stock, it does so on a much smaller radius compared to the flywheel.

The carbon driveshaft is all about tightening up the drivetrain - throttle response improvements are overwhelmingly the result of less flex in the driveshaft over stock.

Carbon is herein used to create a stiffer, more shock absorbing driveshaft that allows to connect the transmission to the differential in a single, stiff piece.

Moment of inertia is addressed with a lighter flywheel.

I have LFW fitted to my S65 DCT and S85 SMG3. I lost 14 lbs off my S85 crank with this. The changes to low to mid range pick up were immense. The carbon driveshaft had no where near the effect these had on that aspect of the driving experience.

[Epoustouflant]

Does this bolt up to a SMG -> manual conversion? They're the same tranny aren't they?

Yes! You'd opt for the 6MT version.

[Bry5on]

Hmm, I thought area moment was mostly relevant to quantify torsion and the mass moment tells you how resistant a body is to changes in rotational velocity. Might need to brush up on things.

Anyway, I also assumed this was the primary motivator for this driveshaft, which is why I asked. Agreed though, this seems like a cool product.

Darn, you’re right, thank you for the correction! Here I am in stress analysis world trying to type between meetings. My mistake. I’ll edit the above!

If OEM 19lb is 3” then an 11lb carbon shaft would need to be under 4” - sounds more like it

[simonnim]

Yes! You'd opt for the 6MT version.

Is it because the SMG shift unit connected to the tranny would get in the way of the flanges or something?

[Epoustouflant]

Is it because the SMG shift unit connected to the tranny would get in the way of the flanges or something?

That's right.

See below. The SMG has the actuators with shifter linkage just above the flange.

[simonnim]

Thank you for the information!