M3 6speed vs DCT

[mixja]

6% less efficient doesn't amount to much - if the car is losing 15% power with the manual solely through the transmission, then the DCT will lose an extra 0.9% power (so maybe 3-4HP using these figures).

[Doc]

In ideal circumstances in same spec cars the DCT will be faster than the manual. In the real world though there are way to many variables and it can be close as in my case. I have seen std 6 speed cars stick with a C63 until 110mph then its bye bye when the AMG starts opening its lungs and pulling away. So a std 6 speed car can be strong out the factory and a DCT can be slower too. Buy what you like to drive and enjoy it is what I say.

[footie]

Originally Posted by mixja

6% less efficient doesn't amount to much - if the car is losing 15% power with the manual solely through the transmission, then the DCT will lose an extra 0.9% power (so maybe 3-4HP using these figures).

If we take it that the total transmission lose for an M3 is 12% what is the split between gearbox, driveshaft, diff and then halfshafts? Say the split goes something like this with the total lose equaling 100%.

Gearbox - 50%, Diff - 30%, driveshaft - 10% and halfshaft - 5% (each)

So out of that 50% lose a DCT is 6% worse off than a manual. Does this sound about right to anyone.

P.S.
Oh, by the way I forgot to add that an automatic is only 2% behind a wet clutch DCT.

[swamp2]

Originally Posted by footie

If we take it that the total transmission lose for an M3 is 12% what is the split between gearbox, driveshaft, diff and then halfshafts? Say the split goes something like this with the total lose equaling 100%.

Gearbox - 50%, Diff - 30%, driveshaft - 10% and halfshaft - 5% (each)

So out of that 50% lose a DCT is 6% worse off than a manual. Does this sound about right to anyone.

P.S.
Oh, by the way I forgot to add that an automatic is only 2% behind a wet clutch DCT.

Sounds high to me. The 50% for the tranny is probably pretty close, which means DCT vs. MT will cost you 50% of 6% or 3% overall, by your figures. For 414 hp that means about 12 hp. I very much doubt it is costing that much. That is a lot of power. Maybe it does during actual clutch movements or some other limited period but once the clutches are fixed (99.9 % of driving time) I can see the clutch lubrication system costing 12 hp. It may be some advertising/marketing effects as well but DCTs are advertised as efficient.

[footie]

I clean forgot about tyre, they are sure to account for at least 15% so quick readjustment is called for. So will readjust gearbox down to 40% of the total tranny lose.

So approx here guys,

414hp (12% tranny) = 50hp
50hp (40% total lose) = 20hp
6% of 20hp = 1.2hp

So if my maths is right the wet clutch is costing us only 1.2hp in normal driving conditions.

[swamp2]

Originally Posted by footie

I clean forgot about tyre, they are sure to account for at least 15% so quick readjustment is called for. So will readjust gearbox down to 40% of the total tranny lose.

So approx here guys,

414hp (12% tranny) = 50hp
50hp (40% total lose) = 20hp
6% of 20hp = 1.2hp

So if my maths is right the wet clutch is costing us only 1.2hp in normal driving conditions.

Lets stop screwing around. Your math is OK but your labels and understanding are clearly incorrect, as are your quoted specs. In the end, through a miracle of multiple errors, you end up about correct.

1. All losses are speed/rpm dependent. Saying a drivetrain has a fixed loss is itself a pretty big approximation. Below about 70 mph a typical car has very little aerodynamic nor tire losses, it is all in the drivetrain. This is why for most "commonly used" speeds and use scenarios the transmission loss is critical to the fuel efficiency. The following chart below shows the principal losses and how they vary vs. speed and gear. This particular simulation used the following losses:

-Auxiliaries: 1%
-Transmission: 6%
-Differential: 2%
-Axles: 5%

Or a total average full drivetrain loss of 14%. With CarTest softwaret this car provided a simulated 1/4 mi of 12.5@113, right about the best we have seen for an M3. You may argue that 14% for the M3 drivetrain is a bit high. We have seen as low as 11% on a dyno but it it certainly in the ball park. You can also argue a bit about the allotment of the 14% among the components but this is pretty decent.

2. Now onto your numbers. The 85% and 91% figures you quoted are absolutely NOT clutch efficiencies ALONE. This document directly from VW provides the numbers and they are for the OVERALL transmission efficiency in 5th gear. Although they do admit a large part of the efficiency gain is from the change from wet to dry clutch.

3. Finally we have an estimate for the wet clutch difference, it is simply:

(91%-85%)x6% = 6%x6% ~ 0.4% ~ 1.5 hp.

If you consider that for a wet clutch DCT the 6% number in my list above might be as high as double that value (based on VWs figures, not BMWs) you can put a range on the benefit of the wet to dry clutch (+other similar efficiency changes from DSG I -> DSG II) for the E9X M3 at:

1-3 hp

Which makes pretty good intuitive sense to me.

Now as incorrect and you have been on various aspects of this part of this discussion, overall your point is quite valid. Dry clutch AMTs can be more efficient than wet clutch ones. As well, higher losses than we have been considering in the past with DCT may be offsetting some of the performance gains we would expect from the twin benefits of super short shift times and improved gear ratios. I would sure like to have exact loss/efficiency figures for the DCT box.

[footie]

Well it seems that by pure luck I did indeed fall on the right figure after all, it's a funny old world. BTW I totally agree with the graph, aerodynamics is the main problem affecting acceleration.

[swamp2]

Originally Posted by footie

Well it seems that by pure luck I did indeed fall on the right figure after all, it's a funny old world. BTW I totally agree with the graph, aerodynamics is the main problem affecting acceleration.

I can't figure out why you would want to congratulate yourself on being right for the wrong reason. It certainly is not admirable. I know you always think you are so clever but you can't prove you are right when right for the wrong reason.

Hmm what huge mistake is next...Aerodynamics is absolutely not the "main problem affecting acceleration". What the graph tells us is that aerodynamic losses expressed in power for vehicles is non linear. And at speeds below about 60 mph losses are dominated by the drivetrain with little to no aero losses, similarly at speeds above about 110 losses are dominated by aerodynamics. At any speed you still have to fight the vehicles mass to accelerate it. The simple way to look at this is:

acceleration = (Power engine - sum all P losses)/(mass x velocity)

Where P engine varies with rpm (obviosuly), sum of all P losses is as per the blue line above and acceleration diminishes to zero when the aero dominanted losses make the two power tems equal, leaving no power left for acceleration. A correct statement would have been that aerodynamic losses are typically the limiter of top speed. That is true when the aero losses are small enough that redline in top gear can be reached.

[footie]

It works for you load of times, what do you say Bruce.

It's this world of black and white you are living in. When I said aerodynamics is the main reason of course I meant as the speed rises, that was surely clear was it not. Since when did acceleration or a race finish at the point when aerodynamic became the main issue.

[bruce.augenstein@comcast.]

Originally Posted by footie

It works for you load of times, what do you say Bruce. ...

Don't sweat it, foot. Just remember you're dealing with that whole flea-floating-down-a-river-on-a-leaf-syndrome, and smile to yourself.

On the other hand, I must say I'm at sea on the issue. When Audi says the dry clutch transmission is 91% efficient vs the wet-clutch efficiency of 85%, they can't possibly mean what I think they mean. With the possible exception of the early Honda CVTs, nobody uses transmissions that eat up that much power. Throwing pretty much any car on a chassis dyno will net you anywhere from 80 to 88 percent net power to the wheels (compared to power at the flywheel), and when you consider everything between flywheel and ground, including increased rolling resistance due to cinching the car down until the springs are screaming, then transmission efficiencies of 83 to 91% just don't compute.

In any event, other than to bug swamp a little, I have nothing of substance to contribute. Intuitively, though, it feels like a minor engineering advantage has been translated by Audi into a fair bit of marketing hand-waving.

Bruce

[footie]

Bruce,

My interpretation of the percentage is the only one to me at least that sounds logical, otherwise the lose would be huge.

[swamp2]

Originally Posted by bruce.augenstein@comcast.

On the other hand, I must say I'm at sea on the issue. When Audi says the dry clutch transmission is 91% efficient vs the wet-clutch efficiency of 85%, they can't possibly mean what I think they mean. With the possible exception of the early Honda CVTs, nobody uses transmissions that eat up that much power. Throwing pretty much any car on a chassis dyno will net you anywhere from 80 to 88 percent net power to the wheels (compared to power at the flywheel), and when you consider everything between flywheel and ground, including increased rolling resistance due to cinching the car down until the springs are screaming, then transmission efficiencies of 83 to 91% just don't compute.

Yup, keep up the insults, I'll keep on topic.

I also think the values quoted by Audi are way too low. Heck they chose an automatic to compare to that offers an 83% efficiency? That must be some pretty darn old automatic tranny technology.

[BIGNTASTIE]

my dct > 6mt all day everdayy

[swamp2]

Originally Posted by footie

It works for you load of times, what do you say Bruce. .

Not so. I'll take specific examples though if you like.

Either way I would rather be wrong with good reasoning (perhaps good at the time, then later found to be wrong) than right with wrong reasoning. Probably a key difference between us - facts/pride/"winning" vs. knowlegde/reasoning/justification.

[2008GT500]

Thanks for the input guys. Great info.

[footie]

Originally Posted by swamp2

Not so. I'll take specific examples though if you like.

Either way I would rather be wrong with good reasoning (perhaps good at the time, then later found to be wrong) than right with wrong reasoning. Probably a key difference between us - facts/pride/"winning" vs. knowlegde/reasoning/justification.

I take it you believe you are the facts/pride/"winning".

Well I would add something to my list and it would read like this 'knowledge/reasoning/justication/facts, the best example of this was the surge.

[swamp2]

Originally Posted by footie

I take it you believe you are the facts/pride/"winning".

Well I would add something to my list and it would read like this 'knowledge/reasoning/justication/facts, the best example of this was the surge.

Foot you are simply unreal. You boast about being right for the wrong reason, I cearly state I would rather fall into the other camp and then try to tell me I am only concerned with facts, pride and winning. Get real. You never cease to truly stun me. Enjoy your twisted little world of being right for the wrong reasons and having no true understanding. Must be fun there.

Again, I am done with the useless back and forth with you.

[bruce.augenstein@comcast.]

Originally Posted by swamp2

...Again, I am done with the useless back and forth with you.

Wow.

Footie, you've silenced the mouth that roared, twice now, all without once responding to his nastiness.

Well done.

Bruce

[swamp2]

Originally Posted by bruce.augenstein@comcast.

Wow.

Footie, you've silenced the mouth that roared, twice now, all without once responding to his nastiness.

Well done.

Bruce

It doesn't mean I have to be done with you.

Your snide little jabs are really mature Bruce as is your fun little alliance with the proud ignoramus. Call that nasty all you want. If you can follow the thread you would realize it is a self inflicted insult. I can't take the credit.

[footie]

Originally Posted by swamp2

It doesn't mean I have to be done with you.

Your snide little jabs are really mature Bruce as is your fun little alliance with the proud ignoramus. Call that nasty all you want. If you can follow the thread you would realize it is a self inflicted insult. I can't take the credit.

Proud ignoramus!

I thought we had finished with the insults, I know I have.

[Great White]

Originally Posted by Doc

LAunch control used(when it worked) on MDCT and M-dynamic launching at 4500 RPM in 6 speed :


3)third run. Launch control does not want to work - high temps detected so we do rolling start to be fair

Nailed him by 3 car lengths easily and pull away (maybe opened up to 5 car lengths) all the way to limiter
DCT- 2 6speed - 1

4)fourth run. DCT launch control back in action
I nail perfect launch and pull away by a bonnet bulge. After 120mph gap opened to 1 car length, hit limiter 2 car lenghts ahead
DCT-2 6speed - 2

5)fifth run. Launch control wont work again.
So rolling we go. Kill him by 2 car lengths and just open up 5 car lengths till limiter.
DCT-2 6speed - 3

The pussy goes home with his tail between his legs silent

DOC I Just wanted to let you know and that you can tell your friend: The usage of the launch control breaks down the by 1/3 of it´s normal life time each time it´s used.
In other words evry time the LC is used your (he´s) killing the clutch just a little bit more and that it overheats is no wonder ! The LC is great to use once for a first time comparison, but after that I would just let it be.
Was a indescrete hint from BMW when I bought the car.
Nice write up, vids would have been nicer though

[swamp2]

Originally Posted by footie

Proud ignoramus!

I thought we had finished with the insults, I know I have.

We are all ignorant in some domains. Ignorant is not really an insult. I know it is hard to believe but one accepted defintion is simply lacking knowledge. It does not mean stupid, which is indeed an insult. Don't forget you are the one who seems to be proud about being right for the wrong reasons.