Slightly OT: Petrol or Diesel?

[usenet2013xxa]

It's on a 2006 diesel C4. It allows a much more relaxed driving style than my wife's petrol Renault.

[Vir Campestris]

Fascinating. I find my highly tuned peaky petrol engine really easy to drive, it'll pull top gear from 30 to 150-ish. I don't often do 150 (OK, never!) but I usually cruise around town in top. Except the road just down from my digs, where cold tickover takes me over the speed limit!

Perhaps is it just Vauxhalls.

Andy

[Dave Plowman (News)]

What I dislike about diesels is the way they hit a 'brick wall' once certain revs are reached. So definitely need to be an auto. ;-)

[Mike Barnes]

"Dave Plowman (News)" :

With an auto and a *petrol* engine you can get optimum acceleration just by putting your right foot down. AIUI it's that ability which is regarded as diesel's major advantage driving-style-wise, and the auto box removes that advantage (leaving no advantage to speak of IME).

[The Natural Philosopher]

That very much depends on the diesel. better breathing and turbos can stop all that.

[John Williamson]

All the diesels I've driven have either a rev limiter or governor, which completely cuts the fuel off once the limit is reached.

[Dave Plowman (News)]

Well, I drove a recent BMW which did just that. And extremely suddenly. A petrol engine usually warns you of coming to the end of its rev range by the power tailing off slightly. Not pull like a train right up to the point where it stops.

Of course I realise it's not a problem in practice as you'd adjust your driving style to it. I simply prefer the characteristics of a decent petrol engine.

[The Natural Philosopher]

None of the ones I have had have had such. Thery simply ran out of torque.

[John Williamson]

In second or third gear?

[Adrian]

They certainly will have had. As has any petrol car that's even vaguely modern.

[The Natural Philosopher]

whatever. I drive both and simply adjust style. Worst diesel I ever drove was a Ford Mondeo. nothing below 2000 reasonable 2000-3000 and nothing over 3500. The BMW 2 TD in the freelander is much better.. turbo comes in sooner, and power tapers off smoothly in the 3000-4000 band. But diesels are pretty much low revving beats anyway. Even the Audi le Mans racing diesel tops out at around 5000 RPM, compared with 18,000 in an F1 car. today is more about turbo charging technology than engine design per se. Variable geometry and multiple turbos can in theory give you any torque curve you want up to the limits of the engine to handle the pressure and RPM.

The lower RPM tens to give longer life. But the high CR means they have to be accuratelty and expensively made.

But the final point is that its not 'diesel versus petrol' but 'which diesel versus which petrol'

I've found Skoda/VW and BMW diesels to be very good. Mercedes and Ford less so. But I don't have an exhaustive experience of either.

[The Natural Philosopher]

Guess I never ran into the limiter then.

with EFI it is in any case a moot point; you can simply start to starve the fuel if the revs get too high if that represents a danger to the engine.

In short you can build whatever you want into the torque versus RPM curves.

[Tim Lamb]

In message , The Natural Philosopher writes

Ford messed up trying to reduce diesel thump by fitting active flywheels.

I understand the 1600cc TDCi engine in our Fiesta is actually from Peugeot?

[Adrian]

There can't be many modern diesel cars without DMFs.

It's a joint venture.

[John Williamson]

Ford and Peugeot were co-operating on engine design in the '80s. The diesel in the 504 was the same down to component level as the one in the Sierra.

[Clive George]

That wasn't cooperating though, that was just buying from PSA. Same as many people did with the XUD.

The more recent thing is a proper JV.

[Dave Plowman (News)]

Not quite sure what you mean. Early diesel autos were often terrible - simply a box set up for a petrol engine bolted on. Modern autos with electronic control can be matched to the individual diesel characteristic far better. Although few will force the diesel to pull hard in a stupidly high gear - despite what many think this has no advantage, except saving the bother of a gearchange in a manual. They'll also lock out the torque convertor in most gears - just using it at low speeds and to cushion changes. Same as they do with petrol engines these days.

[Dave Plowman (News)]

Whatever it is, it is nothing like a decent petrol engine, where the torque output tapers away. Not stops like you've flicked a switch. But you'd not notice it with an auto.

[bert]

Diesels do have a flatter torque curve but the difference is not so great with efi petrols as it was with carbs.

[Clive George]

It's interesting that the fact the diesel still has torque at the rev limit is presented as a problem :-)

It should be possible to design the limiter on a diesel to cut power gradually, but I'm not sure there's much point - that just ends up with everything being slower.

How fast do the racing ones spin?