Well leastwise per the brochure figures.

A petrol with the DSG betters the equivalent manual.

A diesel with the DSG has worst figures than the equivalent manual.

Why?

cheers

marcus

The petrol engines usually use the 7 speed dry clutch box. Most diesels (except I think the 1.6CR) use the 6 speed wet clutch box.

 

The (larger and much heavier) wet clutch box has higher internal losses and so is less efficient than the (much smaller and lighter) dry clutch box.

 

In reality I'd guess there is little in it, the differences are largely academic as manufacturers round mpg figures up/down to the nearest 0.1ltr/100km and the fuel consumption testing is not representive of real world mpg.

More gears the better probably up to a number as high as 9 or 10 as that is what manufacturers re working on.

 

Wet multi-plate gearbox carries about a gallon and a half of oil which have much greater internal friction than the air in the dry clutches but means they can handle more torque as they do not overheat and warp so easy.

 

I think they are lots of other reasons too, petrol engines have less gear changes as their gear change points are higher meaning less changes in a fuel cycle and each gear change requires X Joules of energy to accomplish in a DSG box.

 

There is more to come as other manufacturers a have proof 8 speed boxes are incrementally better than 7 and of course 6 naturally.

 

6 speed box DQ 250 adds about 20 Kgs to vehicle weight and the 7 speed despite more gears only 15 Kgs but it is the friction that is the biggest difference.

 

Wiki.......................................

The first ever worldwide series production DCT was the Volkswagen Group DQ250[10] six-speed dual-clutch transmission,[8] with dual concentric wet multi-plate clutches.[8] It was produced at the Group's Kassel plant[1][2] under exclusive license from Borg-Warner[5][11] for use in transverse powertrain installations, of either front-wheel drive or four-wheel drive (4WD) layouts.[8] The 4WD versions are fundamentally identical to the 2WD versions, but the 4WD versions use an additional bolt-on power take-off unit to direct engine torque to the Haldex Traction rear axle. This DQ250 variant is used in a wide range of models: Volkswagen Passenger Cars (Polo, Golf/Rabbit/Golf Plus, Scirocco, Jetta, Eos, Passat and Touran); Audi cars (A3, and TT); SEAT cars (Ibiza, León, Altea and Toledo); Škoda cars (Octavia and Superb); and Volkswagen Commercial Vehicles (Caddy and T5 Transporter).

A second variant of the Direct-Shift Gearbox went into series production in 2008[9] — the DQ200. This consists of seven forward ratios,[9] but the notable difference over the original DQ250 is the change from wet- to dry-clutches.[2][9] This variant uses two single-plate dry clutches, arranged in a tandem design (instead of concentrically) and are therefore similar in size. The DQ200 is again for use in transverse applications, but is intended for use in smaller cars, with smaller displacement engines that generate relatively low torque outputs.[2][9][10] When used in the latest Golf with the 90 kilowatts (122 PS; 121 hp) engine, this new 7-speed DSG uses roughly 6% (5.9l/100 km for the 7-speed DSG compared to 6.3l/100 km with the manual) less fuel than the same engine with a manual transmission[9] and up to 20% less than a conventional automatic transmission.[9] The original DQ250 also remains available.

==================================================================================================   

Well

DOH!

Gentlemen, I ensure I was comparing apples with apples as I understood both engines used the dry 7 speed DSG.

Which I also know to be significently more frugal than the wet 6 speed in higher torque engines

Which neither of these are.

The 1.2 TSI  vis-a-vis the 1.2TSI/DSGin the Yeti (better figs for the DSG varient)

and happenstance the 1.6TDI vis-a-vis the 1.6TDI/DSG in the Octavia.(better figs for the manual varient)

And if I recall better figs for the 1.4TSI/DSG in the Octavia, than for the manual 1.4TSI also 

OF course what I want is the 1.6TDI/DSG in the Yeti.

See where I am coming from?

Genuinely puzzled at the reason is all.

Since

"Ye canny deny the laws o Physics Captain"

Dieseldogg wrote: "OF course what I want is the 1.6TDI/DSG in the Yeti. See where I am coming from?

Genuinely puzzled at the reason is all. Since "Ye canny deny the laws o Physics Captain" =================================================================================

 

 

The conclusion is that the DQ200 and DQ250 DSG boxes, six or seven speed do not suit the diesel engine as well as the petrol. There are now better boxes ie DQ500/501 that have new features that help fuel consumption.

 

To me it appears down to the engine characteristics meaning that the DSG matched with the diesel is wasting energy hunting around for the optimum gear. Also that 7th gear in the DSG is not appreciably higher than 6th in the manual making a saving their in inertial losses. Do not think they do Yeti with the DSG on the mainland matched to the 1.6D only the 2 litre and only in 4 wheel drive.

 

The 7 speed DSG was principally designed to run in the Polo sized vehicle and was used in the Golf variants on those cars having engines of 250 Nm of torque or less as it was cheaper, lighter etc than using the now ten year old DSG DQ250 6 speed wet. It is likely that VAG have not spent that much R&D time or money on the 7 speed with the diesels as it is principally market is with the petrol variants from 1.2 through to 1.8 TSI engines. 81 mpg extra urban is pretty impressive on the Octy 3 1.6 D with 7 speed DSG if not surprisingly lower compared to the manual's 86 mpg and I wonder if it has the freewheel function in eco mode like it does with the 1.4 TSI. 

 

VAG engineers could postulate more comprehensive answers but would be surprised if the principal reasons are not the great inertial losses in the diesel and compromised gearing as the 7 speed is more designed and optimised for the petrol cars than the diesels.

OK

Getting "warmer" with that explanation lol-lol.

However what are "greater inertial losses in the diesel"?

plus I would have thought the gearing would be set to be correct for the diesel.

Since it is merely a matter of "swopping cogs" = bog standard simple engineering.

plus plus surely the software alogrythms driving the DSG gear changing are required to be diesel-specific anyway.

In that respect I have always felt that the gear ratios are "spot on" in our 1.6TDI/DSG as they mirrored my manual selection in the 1.9TDI Galaxy, in respect of the rev band utilized for normal driving.

i.e. keep the revs low and use the diesel torque.

Or so I mentally noted when first driving the Skoda after the Galaxy.

regards,

Marcus

OK

Getting "warmer" with that explanation lol-lol.

However what are "greater inertial losses in the diesel"?

plus I would have thought the gearing would be set to be correct for the diesel.

Since it is merely a matter of "swopping cogs" = bog standard simple engineering.

plus plus surely the software alogrythms driving the DSG gear changing are required to be diesel-specific anyway.

In that respect I have always felt that the gear ratios are "spot on" in our 1.6TDI/DSG as they mirrored my manual selection in the 1.9TDI Galaxy, in respect of the rev band utilized for normal driving.

i.e. keep the revs low and use the diesel torque.

Or so I mentally noted when first driving the Skoda after the Galaxy.

regards,

Marcus

 

Components of diesels ie crank, pistons etc are heavier than the petrol equivalent and to accelerate them from tickover to optimum change point takes far more energy than the petrol engine.

 

To add to your conundrum as to why a 7 speed DSG on diesel increases fuel consumption where as petrol it tends to improve consumption where you have a diesel model and petrol model of the same hp,, almost the same weight, why is the petrol half to a full second quicker accelerating.  I believe the answer is engine part inertia and that direct injection, turbocharged petrols now have flatter power curves than the diesels which many people have not grasped on to.  The DSG boxes can now efficiently keep the engine using close to where maximum torque and maximum power is available at a smaller percentage of the use-able rev range than the petrols.  Hence even the 7 speed DSG box with it closer ratios, even 6th to 7th is about a 1.2:1 ratio means dropping out of optimum revs.

 

Be interesting to see what the results are when a 8 speed box is rolled out.  VAG has said it is working on a ten speed box too.    

Just to give you some sort of reference a friend has a 1.6 TDi manual and on the urban cycle it returns about 48mpg so a DSG is going to be less, a lot less than the official figures in the 1.6 TDi,

 

The reasons for the OP's question are as said above, one it's friction and two weight, still a fine bit of kit though.

The petrol engines usually use the 7 speed dry clutch box. 

 

My Octavia Vrs has the 6 speed wet DSG box.

The MK7 Golf GTi (petrol) also uses the 6 speed wet DSG as it has better power handling than the 7 Speed dry DSG available in the Golf GT 1.4.

The MK7 Golf GTi (petrol) also uses the 6 speed wet DSG as it has better power handling than the 7 Speed dry DSG available in the Golf GT 1.4.

 

It is the torque handling that is the deciding factor.

 

Petrols which produce their torque higher up the rev range so suit the smaller DSG better.

 

Power = 2 x Pi x revs x Torque.

 

F1 cars only produce about 300 ft lb or torque but do it around 15K revs i seem to recall.

2.0 TDI DSG economy absolutely blows.

 

In all my previous cars doing the same journey to work I could hit 76-89% of government figure.

 

Now, I manage 66%.

 

                                      Gov Figure     Actual     %

Passat 1.9 TDI 130SE          54              48        89

Bora 1.9 TDI 150 Sport        51              39        76

Mondeo ST TDCI                 46              40        86

Audi A4 2.0 TDI                   49               39        79

Skoda 2.0 TDI DSG             63               42        66

 

All cars prior to the Skoda were manual...... All cars after the Skoda will be manual

 

I know it's new and will loosen up but by 9mpg? (to be same average % as my previous cars)

2.0 TDI DSG economy absolutely blows.

 

In all my previous cars doing the same journey to work I could hit 76-89% of government figure.

 

Now, I manage 66%.

 

                                      Gov Figure     Actual     %

Passat 1.9 TDI 130SE          54              48        89

Bora 1.9 TDI 150 Sport        51              39        76

Mondeo ST TDCI                 46              40        86

Audi A4 2.0 TDI                   49               39        79

Skoda 2.0 TDI DSG             63               42        66

 

 

I think we may be getting to the bottom of your MPG problem......You drive your cars like a getaway driver!

 

39 MPG average from a A4 2.0 TDI!.......that's particularly impressive.   

2.0 TDI DSG economy absolutely blows.

 

In all my previous cars doing the same journey to work I could hit 76-89% of government figure.

 

Now, I manage 66%.

 

                                      Gov Figure     Actual     %

Passat 1.9 TDI 130SE          54              48        89

Bora 1.9 TDI 150 Sport        51              39        76

Mondeo ST TDCI                 46              40        86

Audi A4 2.0 TDI                   49               39        79

Skoda 2.0 TDI DSG             63               42        66

 

All cars prior to the Skoda were manual...... All cars after the Skoda will be manual

 

I know it's new and will loosen up but by 9mpg? (to be same average % as my previous cars)

 

This bears out what many of us hae experienced.

 

The 1.9D was absolutely the dog's b**ll*cks.

 

I looked at the 2 litre when it came out and thought where is the technological improvement?  

 

2 mm overbore, better counter-balancing, common rail, all make it nicer but no great technology.

 

The 1.9D stands out a mile in the list above.

 

The Octy 3 could well get 10-15% better but the claimed figures look very ambitious or just plain pie in the sky even for a hyper miler like me which is dissapointing.

 

Is the box using the coast function in eco mode ie revs drop to tick over down slopes?     

Which is why I deliberately avoided the albeit mechanically proven but relatively thristy wet 6 speed DSG.

Opting for the more efficient dry 7 speed.

Which I like, mostly.

Which is why I deliberately avoided the albeit mechanically proven but relatively thristy wet 6 speed DSG.

Opting for the more efficient dry 7 speed.

Which I like, mostly.

 

Until they go wrong - which so many seem to.

This does appear to be true also.

Cept mine (and others) clearly left the factory "wrong"

In respect of software or other related electronic gremlins.

I wonder if the greater interia of the diesel engine is the key to the change?  To match speeds, the engine is "blipped" to match revs on downchanges and this would take energy (fuel) to do so.  If you were changing down in a manual gearbox, you wouldn't (but the ECU does in the DSG)?

 

I'm a petrol + DSG fan though...and like the downchange "blip"

Edited 23 September, 201312 yr by philhoward

The diesel engine takes at least 10K miles before the MPG really starts to improve. My old Octavia MK2 diesel showed a dramatic improvement in MPG as the mileage increased. 9 MPG improvement is quiet possible, perhaps more.