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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Thu, Jan-24-2019, 09:20:32 PM   #61
pbonsalb
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Default Re: J-Fiber E46 M3 CF Driveshaft Review

Quote:
Originally Posted by Pdelamare View Post
Having read the thread about the MFactory drive shaft, Iím suddenly worried about the joint between the tube and the flanges. The new MFactory one is notched between the parts, how serious a problem is this joint failing when itís only relying on bonding adhesive?
All the ones jfiber made for MFactory and fall line and vac for the E9xM3 are doing fine. Have not read of any failures. Mine has been doing fine for over a year.
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Old Fri, Jan-25-2019, 12:42:02 PM   #62
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Default Re: J-Fiber E46 M3 CF Driveshaft Review

Quote:
Originally Posted by TrixyBang View Post
Both statements are very very false in that case, slightly misinformed and, paint half the picture. I've seen some of that on the forum before. Before I start - I am no physicist. This equation requires 10th grade physics so I feel qualified to share.

A heavier flywheel or shaft will have more inertia. Inertia means the object doesn't resist force, but acceleration or force over time. That means that a heavy ball in a vacuum going at 90 mph doesn't need more force to stay at 90 MPH but needs more to stop or to accelerate then a light ball. That menas that more rotational enertia doesn't mean more power to the rear wheels at lets say 4000 rpm, rather more power from 0-4000 rpm depending on the ammount of time taken to get there.

Rotational enertia = 1/2 (mass) x (radius in meters) ^ 2

So the radius does matter a hefty bit.

An Example would be (assumptions only):

Assuming mass is 10 kg for the OEM shaft and radius is 5cm you get:

1/2 X 10 X 0.05*0.05 = 0.0125 kg.m^2 of Innertia


Lets guess aftermarket shaft is 6 kg and radius of 6cm you get:

1/2 X 6 X 0.06*0.06 = 0.0108 kg.m^2 of Innertia which isn't big difference

We know the engine revs to 8000 RPM

As I said at 8000 RPM you are not losing power with one driveshaft compared to the other - at least not a significant amount. However in first gear from 800 - 8000 rpm you rev in 2 seconds, and will use more power to rotate that extra mass than in 4th gear.

Here is the calculation:

To find that you need the rotational moment of innertia. Keep in mind our angular velocity is 700 RPM

RMI = 1/2 * innertia * (angular velocity) ^2

RMI = 0.735 J for the CF driveshaft and 0.8507J for the OEM shaft at 700 RPM

RMI = 96J for the CF driveshaft and 111.11 J for the OEM at 8000 RPM


96-0.735 = 95.265 J difference for the CF shaft

111.11 - 0.8507 = 110.2593 J difference for OEM shaft


Lets say in 4st gear you need 15 seconds to rev from idle to 8000 rpm

For the CF shaft that is the equivalent of 95.265 J / 15s or ~0.0008 hp
For the OEM shaft that is 0.00097hp or a 0.00017hp difference.

Worst case scenario - Gear 1, where you need 2 seconds to rev up and the shaft is rotating at 4.2 times the speed of the engine due to the gearbox being in there. Keep in mind the rotational velocity is now not 700 RPM but 700*4.2:

RMI = 1/2 * innertia * (angular velocity*4.2) ^2

RMI = 12,965 J for the CF driveshaft and 15J for the OEM shaft at 700 RPM

RMI = 1693.4j for the CF Driveshaft and 1960J for the OEM shaft at 8000 RPM

For the CF Driveshaft accelarting for 2 seconds from 700-8000 RPM that is ~1.13hp

For the OEM Driveshaft accelerating for 2 seconds from 700 - 8000 RPM that is ~1.3 hp

So at worst case scenario you are losing 0.27 hp.

I know that is a lot of assumptions, but this is how physics works. Gaining 22hp from a driveshaft is bonkers and wont happen. You can gain acceleration due to weight reduction, but that wont be just the power going slightly up. Power goes up from 800-8000 RPM pull by ~0.3hp in 1st gear as well, so in a 3rd / 4rth gear pull from 5000 rpm the benefits can be outweighed by a 0.1 m/s wind in the opposite direction. Also on a dynostand at 4th gear with 1 to 1 ratio assuming there will be a difference from a driveshaft that can be seen (that 0.0007hp) is also untrue. Dyno variation and a lot of variables will kick ya in the teeth.
^this is exactly why I said "flywheel" and not "drive shaft"-- I was specifically giving an example of an item with an unchanged OD, and avoiding this aspect of the driveshaft discussion.
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Old Fri, Jan-25-2019, 01:08:57 PM   #63
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Default Re: J-Fiber E46 M3 CF Driveshaft Review

Any estimate on how much torque would be lost through the u joint?
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Old Fri, Jan-25-2019, 01:42:19 PM   #64
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Default Re: J-Fiber E46 M3 CF Driveshaft Review

Quote:
Originally Posted by TrixyBang View Post
Both statements are very very false in that case, slightly misinformed and, paint half the picture. I've seen some of that on the forum before. Before I start - I am no physicist. This equation requires 10th grade physics so I feel qualified to share.

A heavier flywheel or shaft will have more inertia. Inertia means the object doesn't resist force, but acceleration or force over time. That means that a heavy ball in a vacuum going at 90 mph doesn't need more force to stay at 90 MPH but needs more to stop or to accelerate then a light ball. That menas that more rotational enertia doesn't mean more power to the rear wheels at lets say 4000 rpm, rather more power from 0-4000 rpm depending on the ammount of time taken to get there.

Rotational enertia = 1/2 (mass) x (radius in meters) ^ 2

So the radius does matter a hefty bit.

An Example would be (assumptions only):

Assuming mass is 10 kg for the OEM shaft and radius is 5cm you get:

1/2 X 10 X 0.05*0.05 = 0.0125 kg.m^2 of Innertia


Lets guess aftermarket shaft is 6 kg and radius of 6cm you get:

1/2 X 6 X 0.06*0.06 = 0.0108 kg.m^2 of Innertia which isn't big difference

We know the engine revs to 8000 RPM

As I said at 8000 RPM you are not losing power with one driveshaft compared to the other - at least not a significant amount. However in first gear from 800 - 8000 rpm you rev in 2 seconds, and will use more power to rotate that extra mass than in 4th gear.

Here is the calculation:

To find that you need the rotational moment of innertia. Keep in mind our angular velocity is 700 RPM

RMI = 1/2 * innertia * (angular velocity) ^2

RMI = 0.735 J for the CF driveshaft and 0.8507J for the OEM shaft at 700 RPM

RMI = 96J for the CF driveshaft and 111.11 J for the OEM at 8000 RPM


96-0.735 = 95.265 J difference for the CF shaft

111.11 - 0.8507 = 110.2593 J difference for OEM shaft


Lets say in 4st gear you need 15 seconds to rev from idle to 8000 rpm

For the CF shaft that is the equivalent of 95.265 J / 15s or ~0.0008 hp
For the OEM shaft that is 0.00097hp or a 0.00017hp difference.

Worst case scenario - Gear 1, where you need 2 seconds to rev up and the shaft is rotating at 4.2 times the speed of the engine due to the gearbox being in there. Keep in mind the rotational velocity is now not 700 RPM but 700*4.2:

RMI = 1/2 * innertia * (angular velocity*4.2) ^2

RMI = 12,965 J for the CF driveshaft and 15J for the OEM shaft at 700 RPM

RMI = 1693.4j for the CF Driveshaft and 1960J for the OEM shaft at 8000 RPM

For the CF Driveshaft accelarting for 2 seconds from 700-8000 RPM that is ~1.13hp

For the OEM Driveshaft accelerating for 2 seconds from 700 - 8000 RPM that is ~1.3 hp

So at worst case scenario you are losing 0.27 hp.

I know that is a lot of assumptions, but this is how physics works. Gaining 22hp from a driveshaft is bonkers and wont happen. You can gain acceleration due to weight reduction, but that wont be just the power going slightly up. Power goes up from 800-8000 RPM pull by ~0.3hp in 1st gear as well, so in a 3rd / 4rth gear pull from 5000 rpm the benefits can be outweighed by a 0.1 m/s wind in the opposite direction. Also on a dynostand at 4th gear with 1 to 1 ratio assuming there will be a difference from a driveshaft that can be seen (that 0.0007hp) is also untrue. Dyno variation and a lot of variables will kick ya in the teeth.
Yeah I estimated 0.25hp in a previous post in this thread
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Old Fri, Jan-25-2019, 03:17:08 PM   #65
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Default Re: J-Fiber E46 M3 CF Driveshaft Review

The biggest improvement is in going from two piece to one piece. Weight savings never hurt and help most with reciprocating mass. Engine builders try to save a few grams on 1 lb pistons. But I agree the power gain, or reduced drivetrain loss, or whatever you want to call it in physics terms, is probably not enough to feel.
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Old Tue, Jan-29-2019, 02:23:12 PM   #66
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Default Re: J-Fiber E46 M3 CF Driveshaft Review

Quote:
Originally Posted by Obioban View Post
^this is exactly why I said "flywheel" and not "drive shaft"-- I was specifically giving an example of an item with an unchanged OD, and avoiding this aspect of the driveshaft discussion.
Calculating Flywheel power is based on the same principle. Only difference is gearing ratios don't factor in. In the comments that followed it seems to me there is a big lack of understanding on the subject so decided to clear things up.

Bottom line, there is no set threshold of power gained from the new driveshaft / flywheel. It depends on how quick you want to rotate it up to what RPM. Mathematically if you want to rotate a heavy flywheel to 15k rpm in 0.00001 seconds you might need more power than a low-powered car can produce.

Quote:
Originally Posted by HassanEido
Yeah I estimated 0.25hp in a previous post in this thread
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Old Tue, Jan-29-2019, 09:21:21 PM   #67
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Default Re: J-Fiber E46 M3 CF Driveshaft Review

^thats basically it.
if you consider inertia as a resistance to move, we then get momentum, which is a resistance to stop.
by reducing inertia in a driveline rotating assy, the available power comes on with less of a delay - at a given moment, more power is sent to the wheels compared to the higher inertia state.
the flipside is that the momentum of the rotating assembly would then keep everything rotating once the power is let off (total energy expended), but in a racecar, we're on the brake preparing for the next corner, so this momentum 'stored' energy scrubbed off as the car slows.
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Old Sun, Jul-21-2019, 10:46:19 PM   #68
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Default Re: J-Fiber E46 M3 CF Driveshaft Review

Finally installed mine, and unfortunately thereís a severe vibration over 130mph. Iíve replied to Jessy to see if thereís anything that can be done.
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Old Wed, Jul-31-2019, 06:45:26 PM   #69
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Default Re: J-Fiber E46 M3 CF Driveshaft Review

Final headcount, I think there are at least 2 with issues on their DS from the group buy. How many of the Group Buy participants have had a flawless experience?
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Old Sun, Aug-04-2019, 04:00:08 PM   #70
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Default Re: J-Fiber E46 M3 CF Driveshaft Review

I’ve replaced my OE drive shaft and the vibration is gone. I’m going to send it back. To say I’m disappointed is an understatement.
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Discussing J-Fiber E46 M3 CF Driveshaft Review in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)