Chris Green laid this down on his screen :
You are of course WRONG!
Diesel driving involves much less gear changing than the narrow torque curve of a petrol engine. My modern BMW diesel has more than adequate torque even below 1000rpm. cc for cc, a diesel produces more power than petrol. It is usually considered that a 2L modern diesel engine equates to a 3L petrol.
Absolutely not so.
Like for like, no diesel produces as much peak power (BHP) as petrol. The torque output may be very different, with diesels usually producing more at low revs.
The big difference is most diesels are turbos. Which gives the effect of a larger engine. But it does exactly the same to a petrol engine too.
A state of the art petrol engine with turbo will out perform a state of the art diesel with turbo if both are the same capacity.
Sure. But diesel power output versus rpm is flatter than petrol. Not that either are anywhere near flat.
NT
Sorry to speak up in what is a technical debate way above my head, but ...
Would some of this debate explain why, when I first got our 2.0l TDI Yeti, it kept stalling when I asked too much of it at very low revs?
Before the Yeti I had a 1.4l petrol Corolla [*loved* it]; I developed the habit of cruising cautiously into a junction or roundabout in 3rd, and if all remained clear, sliding the clutch back in, upping the revs gently, and cruising away.
When I tried this on with the 2.0lt Yeti, it would stall disastrously. I was puzzled, because I'd *always* been told by petrolheads that "oh yeah -- diesels have a lot more torque than petrol".
Just askin' ... carry on chaps!
John
Werl you are both talking bollocks.
With the advent of variabale rate turbos and variable valve timing and electronic fuel injection you can build engines with almost any characteristic you want.
The old rules no longer apply.
In article , Another John writes
VW engine. They seem to have a reputation for that. Down to poor anti-stall management software?
It was true of carbs but since efi and turbos the two types are more equal.
there are other factors at play.
NT
It really does depend on lots of things. You can make a petrol engine that pulls like a train from low revs too.
But as I said, it's more down to the used of a turbo and how hard that blows. And of course it's why diesels cost more than petrol.
Oddly just seen this with my brother's new to him Audi A4 2 litre turbo diesel. Pulls hard (and very nicely) in near any gear within its rev band, but very easy to stall if trying to make it pull from low revs in second. Almost like an on off switch. You simply don't get that with any petrol engine I've ever driven.
In article , Dave Plowman (News) scribeth thus
Thats just what happens with my Audi A6 TDI diseasel too. Too low revs in second loud bang as it stalls but it tootles on around a 1000 revs or a bit above fine otherwise in higher gears!..
Still returns 45 MPG most all the time..
Yes -- after I'd described my own experience (as above) someone else (Sorry! forgot who it was) said "it's more an on/off switch than a stall: engine management system kicking in". And someone else (think it was 'bert') said something equally enlightening ... basically: modern diesels and petrols don't equate _at all_ to the old comparison of the two types.
For which: much thanks, chaps John
I thought I'd look up some figures. It so happens that BMW are very good about publishing figures for their engines.
And it also happens that the ones I looked at don't have a turbo option. It's standard, petrol or diesel. And they don't quote the engine capacity - so not as good as they used to be. (no, a 320 doesn't have a
2 litre engine any more)So I'd be interested in a source confirming your assertions.
Andy
You should because its bollocks.
In general without turbocharging 3 liters of diesel = 2 liters of petrol.
The exact opposite.
Turbos make nonsense of capacity.
1000 bhp out of a 1.6 liter turbo....THOSE were the days.
I've changed from a 3 litre turbo diesel to a 2 litre turbo petrol, both with the same sequential gearbox, the petrol has more 5% more power at higher revs, the diesel had 35% more torque at lower revs.
Despite being a lighter car with theoretically better numbers for 0-60 and 50-75, the petrol feels slightly less powerful overall, at certain revs it changes down to accelerate which feels like all it does is generate more noise for a couple of seconds then change back up, whereas the diesel would have used its grunt to better effect.
Surprisingly, it's easier to get higher mpg out of the petrol both around town and on decent A road journeys, not done so much motorway lately so can't easily say.
I noticed the same difference in noise between a petrol and a diesel version of the same car.
I had a 1.9 turbo diesel Peugeot 306 (non-HDi engine). When I took it to the garage to be serviced they loaned me a 1.8 petrol 308. It was shit-hot for accelerating from rest, but it ran out of puff at motorway speed and had exceptionally poor 50-70 acceleration in either 4th or 5th. Also, being lower-geared, the engine was screaming away at about 3,500 rpm at 70, whereas the diesel did about 2,000. The difference in noise from the faster petrol engine by far compensated for the fact that diesels in general are noisier.
When you say "it's easier to get higher mpg out of the petrol" are you saying that you actually get better consumption from the petrol than the diesel around town and on decent A roads?
I proved how much a diesel car depends on its turbo. A few weeks after I'd had my car in the garage for an unrelated problem, the engine suddenly lost power. It struggled to go up gentle hills, and would not go above about 40 mph. When I looked under the bonnet, I found that the hose from the turbo to the engine intake had come off. Once I put it back on and re-tightened the jubilee clip (which I suspect the garage hadn't done) normal service was resumed. A normally aspirated 1.6 HDi is gutless, one with a turbo goes like a bomb. I was surprised just how much difference it made. Of course the ECU may have detected the fault and deliberately limited the fuel flow rate.
Yes, short shopping trips get 28-30mpg, hour long journeys on A roads get about 40-42, unless I have too much fun of course.
I had to drive the diesel very carefully to get 38 even on a motorway.
Interesting. Though I suppose you aren't quite comparing like with like if it's a 3-litre turbo diesel versus a 2-litre turbo petrol.
Technology has probably advanced quite a bit since I last owned a petrol car - which was as long ago as the mid 90s. Going from a 1.8 petrol fuel-injected Golf (about 35 mpg) to a 1.9 non-HDi Peugeot 306 (about 45 mpg) was a significant improvement, and my present 1.6 HDi Pug 308 has averaged 53 mpg on mainly A roads and motorways (not much stop-start around town) during the 10 years I've had it.
I don't do enough driving of one type only (eg town) to use up a whole tankful of fuel to get a meaningful mpg figure, so I'm not sure how it varies with type of driving. The trip computer gives an estimate of instantaneous (almost meaningless because it varies so much) and average mpg, but there's pretty poor correlation between the average it gives for a tankful and the miles-travelled / fuel-need-to-brim-fill figure. Mind you, different pumps will cut off at different points so I'm not always filling the tank to the same point.
They're not identical cars by any means, 7 years apart.
The petrol has borrowed high pressure common rail injection from the diesel, but doesn't have the variable geometry turbo, presumably because it revs more freely.
The old car used to give numbers for both average and instantaneous mpg, the new one gives numbers for average, but only shows a bar display for instantaneous which is probably better, you can see if you're currently above/below the average without getting distracted by rapidly changing numbers.
Last time I checked I got 69mpg from combined driving.
NT
Bloody hell my old Audi A6 diseasel 2.0 TDI tank estate gives around
43-45 all the time!..HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.