what upgrades needed for M4 Heritage to get close to M4 CS spec/setting

[dezzracer]

Originally Posted by M3SQRD

What do you mean by “Carbon Drive Shaft which was to reduce weight and rotational speed”?

Carbon driveshaft helped reduce overall weight and improves throttle response to wheels. Unless your tracking it the gain is negligible. This was just one of the many slight improvements and changes they made to the CS that made the overall package so good.

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.

[M3SQRD]

Originally Posted by dezzracer

Carbon driveshaft helped reduce overall weight and improves throttle response to wheels. Unless your tracking it the gain is negligible. This was just one of the many slight improvements and changes they made to the CS that made the overall package so good.

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.

Did you actually read what was in bold font? How can switching to a different material reduce the rotational speed of the driveshaft? Switching to/from a CFRP driveshaft has ZERO effect on rpm. You’d need to change the gear ratios in the transmission to change the rpm of the driveshaft. Good try though.

FYI, CF driveshafts were used on base and comp models as well as the gts and cs.

[WhiteFox]

Originally Posted by M3SQRD

What do you mean by “Carbon Drive Shaft which was to reduce weight and rotational speed”?

See note from BMW - cars late 2018 came with steel due to OPF filters

[M3SQRD]

Originally Posted by WhiteFox

See note from BMW - cars late 2018 came with steel due to OPF filters

There’s not a single mention of a CFRP driveshaft and its effect on rpm because there is none. Please highlight the section that states using a CFRP driveshaft reduces rpm? Regardless of the material used to manufacture a driveshaft, the rpm is related to engine rpm and transmission gearing (wheel and output shaft rpm is related to engine rpm, transmission gearing and diff FD ratio but this occurs after the diff). So when BMW switched to a steel driveshaft, the driveshaft rpm in the same transmission gear, which has the same gear ratio (no changes made to the transmission), and turning the same engine rpm, the driveshaft rpm has somehow increased yet the tire road speed remained the same?

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.

[WhiteFox]

Originally Posted by M3SQRD

There’s not a single mention of a CFRP driveshaft and its effect on rpm because there is none. Please highlight the section that states using a CFRP driveshaft reduces rpm? Regardless of the material used to manufacture a driveshaft, the rpm is related to engine rpm and transmission gearing (wheel and output shaft rpm is related to engine rpm, transmission gearing and diff FD ratio but this occurs after the diff). So when BMW switched to a steel driveshaft, the driveshaft rpm in the same transmission gear, which has the same gear ratio (no changes made to the transmission), and turning the same engine rpm, the driveshaft rpm has somehow increased yet the tire road speed remained the same?

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.

Apologies but never said RPM said rotational speed (and was referring to the bending speed) regardless it’s a better drive shaft and was removed late 2018.

[M3SQRD]

Originally Posted by WhiteFox

Apologies but never said RPM said rotational speed (and was referring to the bending speed) regardless it’s a better drive shaft and was removed late 2018.

Yes you did - “Carbon Drive Shaft which was to reduce weight and rotational speed.” Rotational speed is rot/s, rad/s, rpm,…

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.

[swagon]

Originally Posted by Arash666

----

They've not said, ANYWHERE...

what are you on about

[dezzracer]

Originally Posted by M3SQRD

Did you actually read what was in bold font? How can switching to a different material reduce the rotational speed of the driveshaft? Switching to/from a CFRP driveshaft has ZERO effect on rpm. You’d need to change the gear ratios in the transmission to change the rpm of the driveshaft. Good try though.

FYI, CF driveshafts were used on base and comp models as well as the gts and cs.

Relax, no need to be offended. I know what you meant in regards to RPM but thank you for the lesson in physics. I was only explaining the benefits of a significantly lighter driveshaft. It’s similar to using a lightweight wheel, which the CS also has. In addition to reducing overall weight, It takes less power (and time) to get a lighter wheel rotating up to a given RPM. And less brake to get one slowed.

[M3SQRD]

Originally Posted by dezzracer

Relax, no need to be offended. I know what you meant in regards to RPM but thank you for the lesson in physics. I was only explaining the benefits of a significantly lighter driveshaft. It’s similar to using a lightweight wheel, which the CS also has. In addition to reducing overall weight, It takes less power (and time) to get a lighter wheel rotating up to a given RPM. And less brake to get one slowed.

I am relaxed and I certainly wasn’t offended. I asked a simple question and got a response that was answering a question I did not ask. I suppose I should thank you for the physics lesson, too. Like I said, there might be an improvement, albeit really small, in angular acceleration and deceleration but there’s still zero effect on rpm. So how much hp do you think using the CF driveshaft freed up and how much slower are the f8x with a two-piece steel driveshaft?

[F82///M]

Originally Posted by M3SQRD

I am relaxed and I certainly wasn’t offended. I asked a simple question and got a response that was answering a question I did not ask. I suppose I should thank you for the physics lesson, too. Like I said, there might be an improvement, albeit really small, in angular acceleration and deceleration but there’s still zero effect on rpm. So how much hp do you think using the CF driveshaft freed up and how much slower are the f8x with a two-piece steel driveshaft?

7hp and 3nm are free up. Engine rpm response in forward gears is 0.00023 minutes faster while reverse sits at 0.00019.
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.

[WhiteFox]

Originally Posted by F82///M

7hp and 3nm are free up. Engine rpm response in forward gears is 0.00023 minutes faster while reverse sits at 0.00019.
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.

Thanks for the clarity and RPM info - CF has more advantages.

[M3SQRD]

Originally Posted by F82///M

7hp and 3nm are free up. Engine rpm response in forward gears is 0.00023 minutes faster while reverse sits at 0.00019.
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.

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.

[swagon]

Originally Posted by M3SQRD

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.

I'm sure that guy in the orange M4 was the first in the line for the xDrive M4

[M3SQRD]

Originally Posted by swagon

I'm sure that guy in the orange M4 was the first in the line for the xDrive M4

Unless he was a recipient of a Darwin Award before the g8x AWD was released.

[dezzracer]

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/

[M3SQRD]

Originally Posted by dezzracer

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/

Did I ever say CF driveshafts do not have benefits over a steel driveshaft? I asked for clarification on one statement.

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.

[Arash666]

Originally Posted by M3SQRD

There’s not a single mention of a CFRP driveshaft and its effect on rpm because there is none. Please highlight the section that states using a CFRP driveshaft reduces rpm? Regardless of the material used to manufacture a driveshaft, the rpm is related to engine rpm and transmission gearing (wheel and output shaft rpm is related to engine rpm, transmission gearing and diff FD ratio but this occurs after the diff). So when BMW switched to a steel driveshaft, the driveshaft rpm in the same transmission gear, which has the same gear ratio (no changes made to the transmission), and turning the same engine rpm, the driveshaft rpm has somehow increased yet the tire road speed remained the same?

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.

----
I'm a mathematician, now you're talking my language

[dezzracer]

Originally Posted by M3SQRD

Did I ever say CF driveshafts do not have benefits over a steel driveshaft? I asked for clarification on one statement.

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.

Yes, you have made it quite clear you are the smartest man in the room. Congrats!

[M3SQRD]

Originally Posted by dezzracer

Yes, you have made it quite clear you are the smartest man in the room. Congrats!

If that’s what it takes then it’s a pretty low bar

[F82///M]

Originally Posted by M3SQRD

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.

Dyno test was done on same day, just different locations. One in Canadian winter, other was in Australian summer, different cars, comp dct VS base 6 speed, different dynos. It was all taken into consideration so results are true from secret formula.

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.

[M3SQRD]

Originally Posted by F82///M

Dyno test was done on same day, just different locations. One in Canadian winter, other was in Australian summer, different cars, comp dct VS base 6 speed, different dynos. It was all taken into consideration so results are true from secret formula.

Different cars with different transmission trams and with different trans types and different engines and different dynos with different inertias with very different ambient weather conditions and done in different gears and different diffs and different wheel-tire mass/inertia and…yet somehow your secret formula isolated and unequivocally confirmed the 7 hp and 3 N-m are all due to different driveshafts and only different driveshafts. Repeatability on the same dyno and differences in tie down and differences in fans/airflow and differences…can produce 7 hp and 3 N-m differences, excluding all other listed differences. Good story

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.

13 msec and 11 ms in forward and reverse gears, respectively, are all 100% unequivocally due to and only due to different driveshafts and none of the other differences listed above? You do know no two cars, more specifically two engines, have the same throttle response and identical driveline inertias, even for cars with the same transmission and same driveshaft material? You’re talking about a max time difference of 13 msec between two different cars with different build configurations. What were the measured changes in tire pressures due to radiator locations on different cars? You do realize no two cars come with the exact same overall weight, weight distribution, overall inertia, inertia distributions, driveline losses especially when different trans types are used, etc. but 100% of the differences are due to only different material driveshafts? Yeah, yeah, the secret formula

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.

You didn’t include the differences in tire pressure due to different ambient temperature which is likely much higher than the temperature changes due to radiator locations. Were these tests done on a dyno or in the real world with real airflow over and through the car? What were the magnitude of, or the actual changes in, tire temperatures due supposedly to only radiator locations? When I come off the track and have my tire pressures checked in pit lane, I don’t see significant differences in F tire pressures and in R tire pressures with my asymmetrically placed radiators and their effect on tire pressure. I wonder why I don’t see this? This discussion was about different driveshaft materials so how does a driveshaft of different material affect the tire temperatures? Damn, the Sun for being on the right side, and, on the same day, potentially on the left side, too, of the car. Someone needs to develop a system that continually adjusts the tire temperatures otherwise you’re going to crash because BMW didn’t account for different tire pressures caused by asymmetrically placed radiators. I wonder why more race cars don’t crash when starting with low tire pressures, asymmetrically placed radiators and the direction of the Sun changing as a lap is completed with a different number of left and right corners…It must be the secret formula again.

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.

What? The oil viscosity was altered because of different weight distributions, different inertia distributions, different location of the Sun, asymmetrically placed radiators, driveshaft materials, etc. AND now oil viscosity was altered to address all of the differences that have existed on any mass produced car AND the Sun needs to be on the right side of your car? Sure. Now we have better tire temperatures and weight distributions that prove RHD is superior to LHD, even with the change in oil viscosity, changing location of the Sun and, somehow, the change in driveshaft material. BMW screwed up when they elected to make LHD f82 GT4s.

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.

A ~6 kg driveshaft mass change coupled with a DCT increases your probability of having a SCH? Show me data that definitively shows DCT cars have a higher probability of having a SCH AND the probability increases if you a steel driveshaft coupled with a DCT? Wait, it’s the mass, not driveline inertia, of the DCT that increases your probability of having a SCH?

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!