|
Post Reply |
|
Thread Tools | Search this Thread |
04-06-2024, 04:55 AM | #23 | |
Major
1183
Rep 1,221
Posts |
Quote:
If OP wants to change under the bonnet only then just a tune. Personally I would leave that beautiful Heritage alone. M cars are so good from factory I’m of the opinion you often do not improve but rather detract from what factory BMW engineers and drivers put together in a package. Not to mention most problems I see in forum posts are on cars that have been “modified “ in some form or shape. |
|
Appreciate
1
Arash6664.00 |
04-06-2024, 06:01 AM | #24 | |
Major General
2276
Rep 5,707
Posts |
Quote:
FYI, CF driveshafts were used on base and comp models as well as the gts and cs. Last edited by M3SQRD; 04-06-2024 at 09:30 AM.. |
|
Appreciate
1
Arash6664.00 |
04-06-2024, 08:29 AM | #25 |
Second Lieutenant
125
Rep 253
Posts |
See note from BMW - cars late 2018 came with steel due to OPF filters
|
Appreciate
0
|
04-06-2024, 09:17 AM | #26 | |
Major General
2276
Rep 5,707
Posts |
Quote:
Wheel speed = (pi * engine rpm * wheel radius) / (30 * trans gear ratio * diff FD ratio) The driveshaft transfers the angular velocity from the transmission output shaft to the diff pinion gear and the diff then splits it the half shafts via the drive gear. So based on the equation or description above, where and how does a driveshaft made of either steel or CFRP alter the driveshaft rpm? The CFRP driveshaft may have a very small effect on the rate of change of rpm (i.e., angular acceleration) due to lower rotational inertia compared to a steel driveshaft. “Critical bending speed” is actually increased with the use of CFRP which eliminates the need for a central mount on the driveshaft (i.e., use a one-piece driveshaft). This doesn’t increase or decrease, or alter, the rpm which, again, is based on engine rpm and transmission gearing. |
|
Appreciate
0
|
04-06-2024, 10:32 AM | #27 | |
Second Lieutenant
125
Rep 253
Posts |
Quote:
|
|
Appreciate
0
|
04-06-2024, 11:13 AM | #28 | |
Major General
2276
Rep 5,707
Posts |
Quote:
Ok but your statement is still incorrect. The critical bending speed, which is the rotational velocity of a shaft that excites the out-of-plane primary lateral bending mode of the shaft (i.e., an instability/bifurcation point is reached, similar to flutter and buckling), has to INCREASE, not decrease/reduce, to be able to use a one-piece driveshaft. A properly designed CFRP driveshaft’s critical bending speed is higher than a steel driveshaft’s critical bending speed. BMW had to add a central support to the two-piece steel driveshaft. In this application of CFRP does not “reduce” the “rotational speed” of the driveshaft. |
|
Appreciate
1
Arash6664.00 |
04-07-2024, 01:19 AM | #30 | |
Major
1183
Rep 1,221
Posts |
Quote:
|
|
Appreciate
0
|
04-07-2024, 07:38 AM | #31 | |
Major General
2276
Rep 5,707
Posts |
Quote:
|
|
Appreciate
0
|
04-07-2024, 12:08 PM | #32 | |
Private First Class
78
Rep 138
Posts |
Quote:
There's increased possibly of crashing the vehicle with CF shaft due to uneven tire pressure upon hard acceleration. Steel driveshaft cars are not only slower by that much but also less efficient while using 0w30 BMW LL01FE engine oil. Even bigger problem is extra 5.7kg + weight of new exhaust parts which translates into faster overall wear and tear along with higher risk of spinning the crank hub. It's hard to say which is better since both have positive and negative effects. I'd say CF has advantages because one piece shaft is better than two or three piece shaft as long as tire pressures are watched closely. |
|
Appreciate
0
|
04-07-2024, 12:10 PM | #33 | |
Second Lieutenant
125
Rep 253
Posts |
Quote:
|
|
Appreciate
1
F82///M78.00 |
04-07-2024, 01:58 PM | #34 | |
Major General
2276
Rep 5,707
Posts |
Quote:
7 hp and 3 N-m is within the accuracy of a dyno. So this dyno test was done on the same car with both a CF and steel driveshaft and on the same dyno and on the same day? Even with all of that, 7 hp and 3 N-m is within the repeatability of a dyno and your sample size was probably 1. This testing wasn’t done by BMW because their power numbers are based on an engine dyno (i.e., no driveshaft). What exactly is the 0.013 sec and 0.0114 sec improvement/difference and how does it relate to an increased probability of crashing because you have a CF driveshaft with uneven tire pressures for a duration of 13 msec? I’d love to know what causes the uneven tire pressures and what’s the magnitude of the uneven pressures? What’s the correlation between driveshaft material and engine oil viscosity? S55 oem oil viscosity was changed from 5W30 to 0W30 in 2016 when CF driveshafts were solely used on all f8x models (base, comp and gts). CF driveshafts were used in all models until 2018. However, somehow the oil viscosity switch back in 2016 was due to the switch to steel driveshafts in 2018 - seriously? It just keeps getting better. An additional 5.7 kg + unspecified amount of extra opf exhaust mass utterly destroys your car due to the additional wear and tear AND, somehow, increases the probability of spinning your crankhub. I’d love to see the supporting data used to draw these conclusions. So it’s not tire pressures alone that cause people to crash leaving C&Cs, it’s the CF driveshaft and the associated 13 msec uneven tire pressures that causes people to crash leaving C&Cs. |
|
Appreciate
0
|
04-07-2024, 05:24 PM | #36 |
Major General
2276
Rep 5,707
Posts |
|
Appreciate
0
|
04-08-2024, 02:33 AM | #37 |
Major
1183
Rep 1,221
Posts |
Now that you keyboard comedian’s have had your fun here are some published benefits of a carbon fiber driveshaft.
https://www.motortrend.com/how-to/th...afts-from-qa1/ |
Appreciate
1
Arash6664.00 |
04-08-2024, 06:00 AM | #38 | |
Major General
2276
Rep 5,707
Posts |
Quote:
I’ve been designing, analyzing, fabricating and structurally qualifying complex composite structures since the early 1990s. I do understand the advantages and disadvantages of using composite materials. Last edited by M3SQRD; 04-08-2024 at 10:02 AM.. |
|
Appreciate
0
|
04-08-2024, 04:12 PM | #39 | |
New Member
4
Rep 23
Posts |
Quote:
I'm a mathematician, now you're talking my language Last edited by Arash666; 04-08-2024 at 04:22 PM.. |
|
Appreciate
0
|
04-11-2024, 01:45 AM | #40 | |
Major
1183
Rep 1,221
Posts |
Quote:
|
|
Appreciate
0
|
04-11-2024, 01:51 AM | #41 |
Major General
2276
Rep 5,707
Posts |
|
Appreciate
0
|
04-11-2024, 01:41 PM | #42 | |
Private First Class
78
Rep 138
Posts |
Quote:
Improvement was the time it takes from 750 to 7500rpms in all forward and reverse gears respectively. Uneven tire pressure comes from uneven weight distribution, along with uneven radiators temperatures on left and right sides, directly influencing higher difference front to back tires. Crashing comes from RR tire being coldest due to low temp radiator on that side and over pressurized rear left tire from high temp radiator on this side along with extra weight from driver. This was somewhat corrected on dyno run in Australia with driver and Sun being on right side of the car while in Canada was overcast that day. Engine oil correlation comes from lower oil viscosity to counteract all above mentioned differences. Yes, cars from '16 to '18 were fastest. On top of that, our dyno test confirmed that RHD models have better tire temperature and weight balance, as long as the Sun is on the drivers side. Crankhub spin comes from extra weight engine has to deal with. Example dct vs 6 speed, dct is heavier and more prone to spinning crankhub. This will be our next test to confirm, just waiting for winter in Australia. |
|
Appreciate
0
|
04-11-2024, 05:35 PM | #43 | |
Major General
2276
Rep 5,707
Posts |
Quote:
This question applies to all of your theories, what was your sample size and the low (two) sample size statistical analyses that support your assertions? The best you’ve proved is no two cars will have the same measured engine output, potential loss difference of DCT vs. MT, the same weight and inertia, the same weight and inertia distributions, and tire temperatures change with ambient temperatures, heat and the different relative positions of the Sun. Yet, somehow, you were able to unequivocally demonstrate all of this is due to changing the driveshaft material from CF to steel. Ok, sure. I’m surprised your skills aren’t being actively and aggressively fought over by car manufacturers because their current engineers missed so many different things that resulted in loss of throttle response, different weight and inertia distributions, wildly different tire temperatures that result in greater probability of being in an accident, increased engine wear and tear from an additional ~7 kg and change in oil viscosity and higher probability of a SCH, and weight/inertia and temperatures are better distributed on RHD models. Awesome work done on two very different cars! |
|
Appreciate
0
|
Post Reply |
Bookmarks |
|
|