DCT vs. ZF8?

[BimmerBoomer]

I've owned both, but don't let that stop you from offering your "experience". Anyone have anything objective to say here?

[gmd2003]

Originally Posted by BimmerBoomer

I've owned both, but don't let that stop you from offering your "experience". Anyone have anything objective to say here?

Here's a Vbox GPS graph of my M6 with DCT accelerating 0-140ish . 0 interruption of power , is that objective enough ? Lol

[MRV99]

I currently have a DCT and a 8ZF and they feel very different. Don't get me wrong , the ZF is a great transmission but it is not the same as a DCT. In light all around driving the 8ZF fits the bill but in aggressive driving the control and feel of the DCT is very apparent.

[mkoesel]

Originally Posted by CanAutM3

^This

The direct connection between engine and drive wheels is the main benefit. A regular automatic can be programmed to shift extremely fast, but the power still needs to be transmitted through the torque converter.

I would argue that it isn't just the use of the clutch instead of a torque converter that makes the DCT better than the ZF8 (or other transmission that uses a torque converter), but the fact that it has two clutches, each routing power through their own separate output shafts. This means the car can be in gear constantly while accelerating with uninterrupted power to the drive wheels.

So, even the Mercedes MCT, for example, which does not have a torque converter, is still at a disadvantage vs. a DCT. Same issue with the Aston Martin gearbox which, unlike the Mercedes, uses a stepped gear train just like a DCT or manual.

[CanAutM3]

Originally Posted by mkoesel

I would argue that it isn't just the use of the clutch instead of a torque converter that makes the DCT better than the ZF8 (or other transmission that uses a torque converter), but the fact that it has two clutches, each routing power through their own separate output shafts. This means the car can be in gear constantly while accelerating with uninterrupted power to the drive wheels.

So, even the Mercedes MCT, for example, which does not have a torque converter, is still at a disadvantage vs. a DCT. Same issue with the Aston Martin gearbox which, unlike the Mercedes, uses a stepped gear train just like a DCT or manual.

I am not an expert in automatic transmissions, but my understanding is that it is also possible to execute shifts without interrupting the power to the drive wheels with them.

[BimmerBoomer]

However, having two shafts rather than one may help to explain 80 millisecond rather than 200 millisecond shift times.

[tooch]

Its just better

[CanAutM3]

Originally Posted by BimmerBoomer

However, having two shafts rather than one may help to explain 80 millisecond rather than 200 millisecond shift times.

If the shift can be executed without interruption of power delivery, the time it takes to complete the shift is irrelevant.

[mkoesel]

Originally Posted by CanAutM3

I am not an expert in automatic transmissions, but my understanding is that it is also possible to execute shifts without interrupting the power to the drive wheels with them.

Theoretically. But - and I'm no expert either mind you - I don't think they can overlap the gear engagement can they? I guess it depends on how the friction bands are actuated.

[M6-Coupe]

I think this video answers all questions

[tdizzle]

Originally Posted by M6-Coupe

I think this video answers all questions

Sporty. For sports cars.

[Jeffman]

Great vid! My next car will have one.

[font9a]

>> One thing that hasn't been pointed out is that DCT's tend to have lower torque/HP ratings.

The stock 7-speed M-DCT is rated to 540 Nm.

[ake]

Originally Posted by font9a

>> One thing that hasn't been pointed out is that DCT's tend to have lower torque/HP ratings.

The stock 7-speed M-DCT is rated to 540 Nm.

So you are saying the MT is capable to handle more NM?
I thought I read somewhere that the DCT can go up to 600NM.

[Sapper_M3]

Originally Posted by CanAutM3

The ZF 8 speed still has a torque converter, which is the main contributor to the "disconnected" feel of traditional automatic gearboxes. From my perspective, I feel the same connection from the engine to the wheels in a DCT compared to a standard manual. This makes sporty driving much more enjoyable.

The counterpoint is that the "disconect", through the viscous fluid in the torque converter, also contributes to make an "automatic" transmission much smoother in operation compared to DCT.

Better fuel economy could be achieved by making the 7th gear in the DCT much longer while keeping the ratio from 1 to 6 closely spaced. Who uses 7th at the track anyway .

7th gear is used at the track when the red mist takes hold and you suddenly realize you're completely out of fuel just past pit lane on a 3.5 mile road course.

[Powaup]

Originally Posted by BimmerBoomer

I've owned both, but don't let that stop you from offering your "experience". Anyone have anything objective to say here?

Hey on the topic of DCT vs ZF8... The Zf8 has a function if you mash the pedal to the floor it will downshift even if you are in manual mode. Also, the tranny will up shift a gear for you if you hit the redline. Can this be disabled? And does the DCT have the same feature?

[CanAutM3]

Originally Posted by Powaup

Hey on the topic of DCT vs ZF8... The Zf8 has a function if you mash the pedal to the floor it will downshift even if you are in manual mode. Also, the tranny will up shift a gear for you if you hit the redline. Can this be disabled? And does the DCT have the same feature?

It is all a question of programming. The DCT in the M3 application was programmed to behave more closely to a MT while in the 135/335 application it was programmed to be more akin to an AT in behavior.

In ///M cars, the DCT will not downshift or upshift unless you ask it to with the paddles or the lever. It will bump on rev limiter without upshifting and will stay in the selected gear even if you floor the throttle all the way.

One cool feature in manual mode, if you simultaneously floor the throttle to engage the "kickdown" and pull and hold the left paddle, the DCT will automatically downshift the required quantity of gears (skipping gears) to get you optimal acceleration.

[Powaup]

Originally Posted by CanAutM3

It is all a question of programming. The DCT in the M3 application was programmed to behave more closely to a MT while in the 135/335 application it was programmed to be more akin to an AT in behavior.

In ///M cars, the DCT will not downshift or upshift unless you ask it to with the paddles or the lever. It will bump on rev limiter without upshifting and will stay in the selected gear even if you floor the throttle all the way.

One cool feature in manual mode, if you simultaneously floor the throttle to engage the "kickdown" and pull and hold the left paddle, the DCT will automatically downshift the required quantity of gears (skipping gears) to get you optimal acceleration.

That is pretty cool indeed.

Is it possible to program the ZF8 to behave like the DCT? As in no downshift when going past kickdown and no upshift when reaching the redline

[svc0x80]

Originally Posted by ake

So you are saying the MT is capable to handle more NM?
I thought I read somewhere that the DCT can go up to 600NM.

Getrag DCTs are either 700 NM or 750NM. Considering the M4 already puts down 550nm of torque...I figure we'll at least get the 700 NM rated DCT.

[swamp2]

Originally Posted by gmd2003

Here's a Vbox GPS graph of my M6 with DCT accelerating 0-140ish . 0 interruption of power , is that objective enough ? Lol

Although at the typical testing resolution of a Vbox, or the equipment used by journalists, the power flow appears full uninterrupted. However, if one were to look at the curves with a much higher sampling rate (and appropriate filtering), one would see that shifts are ever so slightly interrupted, it is just about an order of magnitude less time than it takes to shift a MT. Any reasonably sensitive butt-o-meter can note this sensation and interruption.

[gmd2003]

Originally Posted by swamp2

Although at the typical testing resolution of a Vbox, or the equipment used by journalists, the power flow appears full uninterrupted. However, if one were to look at the curves with a much higher sampling rate (and appropriate filtering), one would see that shifts are ever so slightly interrupted, it is just about an order of magnitude less time than it takes to shift a MT. Any reasonably sensitive butt-o-meter can note this sensation and interruption.

The sampling rate is 20hz and you can look at the graph on any scale and there is no interruption of acceleration only a slight change of acc slope . And my butt o meter doesn't detect a momentary coasting , the DCT in S3 at redline shifts faster than my 2007 E 92 M3 and my 2010 GTR did I according to my butt on meter and data logging . Sure at 20 times a second there is a gap in the data but less than .05 seconds is not detectable by me .

[swamp2]

Originally Posted by gmd2003

The sampling rate is 20hz and you can look at the graph on any scale and there is no interruption of acceleration only a slight change of acc slope . And my butt o meter doesn't detect a momentary coasting , the DCT in S3 at redline shifts faster than my 2007 E 92 M3 and my 2010 GTR did I according to my butt on meter and data logging . Sure at 20 times a second there is a gap in the data but less than .05 seconds is not detectable by me .

Interesting. Unless your M-DCT is an entirely different concept and specification to that in my E92 M3, I find it nearly inconceivable that you don't feel the shifts. I know the unit has been improved, as pretty well all products do from generation to generation. However, I think it is fair to call this evolution in DCTs, not a revolution (again from E92 M3 to M6). I suppose you can debate "feeling the shift" vs. "an interruption of power" vs. "feeling coasting" as being different, but to me they are one and the same.

Look, don't get me wrong, I am a HUGE DCT fan, of both the engineering and driver experience. The shifts in my car are impressively fast, but they do vary in swiftness and feel substantially depending on mode and throttle position. Although in general they are nearly seamless, my butt-o-meter nearly always tells me when shifts happen.