New to me auto.

Just got a car fitted with a 7 speed twin clutch twin layshaft automated synchro gearbox. Which they call a PDK. Last version of this I drove some
years ago was a single clutch type (BMW SMG), which was dreadfully clunky at lowish speeds.
This one when driving normally in town changes just as sweetly as a slush pump type. Although the absence of a torque convertor makes the first few yards from rest not quite so smooth.
Having 7 gears, it has a much higher top gear giving much more relaxed cruising than the previous ZF 5HP. Admittedly an old slush pump box these days, though.
To say I'm impressed would be an understatement. ;-)
The other odd thing is it is programmed like I'd have done myself. Always in the gear I'd be using if a manual. Unlike the previous ZF that couldn't seem to decide which gear to use.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I thought DSG / PDK type boxes were the future, until I got something with the ZF 8HP.
--
Steve H

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Quite - be very interesting to compare the two on the same model. With the same programmers.
The only time I feel the lack of a TC is at very low engine speeds where the TC would even out any slight vibration. Being very picky, though.
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Just to add, I'd guess the epicyclic box would still win out in terms of absolute refinement. Why Jaguar - always known for the best compromise between performance and refinement - probably stay with it. Be interesting to know how the two compare cost wise in manufacture too.
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I think Jag are using the ZF 8HP these days - mind you, who isn't? - and I think the Evoque uses the 9HP transverse application.
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Wonder if there is a limit to how many gears before no added benefit? Must add weight to some extent.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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As we move away from peaky diesels, I think things will start to get a bit more sensible again.
And hybrids really lend themselves to a planetary operation like the Toyota Hybrid Synergy Drive system.
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On 01-May-18 4:49 PM, Steve H wrote:

Toyota's PSD works like a differential.
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On 01/05/2018 16:49, Steve H wrote:

??. the original problem with diesels was that they produced so much low-down torque that no auto box of the era could cope.
Auto diesel cars were very rare 20 years ago.
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More that older car diesels were so pedestrian you couldn't afford the power losses.

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Dave Plowman (News) wrote:

Even more than that, Diesel was the cheapskate option. Throwing away economy with an autobox - that'd never do!
Years ago a friend had a Mk II Mondeo 1.8D which confused people as it was either a Ghia or had all the Ghia options. They were more normally LXs.
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In the early days, diesels came at a considerable premium. So only bought by those doing enough miles to justify the cost - and who weren't in a hurry. Or valued their ears. ;-)

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On 02-May-18 11:25 AM, Dave Plowman (News) wrote:

Merc 300D Auto outsold the manual box. An adequate 134bhp 3L (44 bhp/L) 6 cylinder Diesel may have had something to do with that.
https://www.howmanyleft.co.uk/?utf8=%E2%9C%93&q=mercedes+300d
Crappy 56bhp 1.7L (33 bhp/L) Astra "j" Diesel Auto without a turbo now that would be the ultimate turkey of a car. Could have been rivaled by the 59bhp VW Polo SDi if they hadn't had the good sense to not make an auto version.
https://www.howmanyleft.co.uk/?utf8=%E2%9C%93&q=astra+diesel+auto
Turbo Diesels were a game changer. These days a 1.7 turbo diesel can easily run an auto box. Generation later Astra G after 2007 came with 108bhp 1.7 turbo diesel. Not much short of the 114bhp of the Pinto in a Ford Capri 2.0L Laser Injection.
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Even the smallest diesel could be OK with a decent auto box. As good as a manual. But a 7 speed auto is likely going to add too much cost to a cheapish car.
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well it was possible as all the fire engines of that era had 10litre perkings diesels and autoboxes
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On 02/05/18 15:50, Mark wrote:

Indeed, but also the size to fit a hefty autobox. Harder in a FWD hatchback :-)
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And many buses. Rather more than 20 years ago.
Not that where the torque is developed matters much to an auto. Like most gearboxes, it's the maximum torque that matters.

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Diesels have a tiny power band. Like 2k rpm to 4k rpm, on a good day. This is why you now have gearboxes with 8 or 9 ratios.
That's a much smaller band of usable power than a modern turbo petrol, which will get away with a fewer number of ratios.
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On 02-May-18 8:31 PM, Steve H wrote:

Extra Lower gear is to help it pull away fully laden with a trailer. It's only a little "downsized" engine but has the power of something 2x the size so needs a bit of help getting off the line. Extra "double" overdrives are to reduce engine speed for better mpg. So you really only have a 5 speed + low + double overdrive. Needs more stirring than a manual 4 speed + overdrive or a 3 speed auto + overdrive.

2K to 4K range on an engine with a 4.5K rpm peak speed is very good. 44% of the rev range is usable.
Now take a typical normally aspirated SI engine. Peak power is at 6k rpm, peak torque 4k rpm, redline 6.5k rpm. 2.5k rpm range is 38% of total range.
So you have a 6 speed Corvette C5, 400bhp 6k rpm, peak torque 4.4K rpm. Just 32% usable range. As it has a "double overdrive" in 6th at 70 mph it's way outside the usable range at 1.55K rpm.
You should never look at the numbers. What counts is the number/peak.
Don't need a "modern" SI turbo. 1988 Nissan CA18DET, redline 7.2K rpm, peak power 6.4K rpm, peak torque 3k rpm. Usable range 58%, 65mph > 140mph in top (not an overdrive, 140mph = 6.4K rpm), 4th 55 mph > 133 mph, 3rd 42mph > 100 mph, 2nd 27.7 mph > 66 mph and 1st 16mph > 38 mph. With an overdrive it would be outside its "usable" range at 65-70mph.
The issue with turbos for many is the lack of engine "lugging" torque and the Jekyll and Hyde nature of the engine. Just 500 rpm below peak torque they drive like a N/A engine in need of a tune up. This causes much hardship as one has to think about stirring the gears. Better get an auto which won't let one use "lugging" torque to accelerate, press the go pedal and its down though the gears.
What most people really want is an electric motor but they just don't know it yet. Peak torque from ZERO all the way to peak power and then peak power all the way to the redline. 100% usable range, no need for gears as it will wheelspin off the line and reach top speed all in one gear.
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This was certainly the problem with early auto diesels. The very low output ones car used before turbos arrived. The auto was made for the wider power band of a petrol engine, so didn't have enough gears.

But most petrol engines ain't turbos.

Are you implying the torque goes from near zero to peak in a few hundred rpm? Be a very odd road engine indeed that did that.

Complete bollocks, as they say. You don't need peak torque on a powerful vehicle to cruise at 70 mph. All you need is enough torque to maintain that speed. My car has a peak RPM over 7000, but cruises at under 2000 rpm at 70 in top gear.

If you had 'peak BHP' over a wide RPM band, it means the torque is falling away in proportion to the RPM.
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