"My Focus 1.6 TDCi copes with everything thrown at it, short journeys, medium, long, slow speeds, stop/start etc. I've never had any problems with the DPF. "
With such a mix of journeys you never should have a DPF problem - I've never had one either, but doing 15k+ a year of mixed driving I don't expect to.
8,000 mainly town miles may cause problems - I suggest the OP reads the sections in the handbook about DPFs before commiting to a DPF car.
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When it comes to acceleration much (if not all) of the higher engine output torque of a diesel compared with a petrol is cancelled out by the higher gearing.
I'm not sure thats true. Why do turbo diesels literally fling you up the road on a big gob of torque with the slightest sqeeze on the throttle then?
Why can overtakes be executed with huge thrust compared to winding up a petrol into a frenzy then grabbing another gear mid-manoeuvre?
I'veyet to come up behind a 1.9 or 2 litre diesel which has been able to accelerate away from my 2 litre petrol.
I had the freak of chance to drive a manual BMW 325iSE and a 130 Golf GTTDi back to back over the same urban route within an hour of each other through having to borrow company cars to run an errand.
The Golf had 130 BHP, the 325i 192 BHP.
All I can tell you was that the Golf felt significantly faster and more relaxing to drive, the BMW felt limp and gutless. Only when I reached a dual carriageway and allowed the BMW its head, did it then feel significantly faster than the Golf.
How many times you plant your foot wide open on the throttle in daily driving I dont know - maybe when entering a motorway.
Bottom line:- Golf 1 BMW Nil. (I'm not pro Golf or VAG Td particularly just telling it like I found it)
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>> When it comes to acceleration much (if not all) of the higher engine output torque >> of a diesel compared with a petrol is cancelled out by the higher gearing. I'm not sure thats true.
To prove that it's true, you only have to calculate the torque at the road wheels (which, for similar rolling radius tyres, is the relevant parameter) by multiplying the engine output torque by the ratio of the rotational speed of the wheels to the rotational speed of the engine, to take into account the higher gearing of a diesel. It's just a matter of simple arithmetic.
Edited by L'escargot on 07/07/2009 at 07:44
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If you want an example of diesel reliability, a friend of mine has an Alfa Romeo 2.4FJTD Sportwagon that has been chipped to 200bhp. Over the 115k miles he's had it, the engine hasn't caused any problems.
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I know the maths, but I also know what the seat of my pants tells me.
Driven "normally" a turbo diesel "feels" quicker and seems able to keep its speed more when encountering a hill.
Probably due to how the engine can keep piling on the torque.
Another example, my CDTi 150 Astra "feels" quicker in any gear you want to name than my old 200bhp turbo Rover 620ti. It'll throw you up a hill - If you live somewhere flat, you may not fully appreciate this phenomenon. A wheel spin competition or an outright dual carriageway drag and the Rover would win it.
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I completely agree, David.
SWMBO's Golf GT TDI (130 bhp) feels far perkier than my 180 bhp Volvo S60 2.0T petrol until you get it on open roads and start using the revs. Then you feel the petrol's ability to sustain the acceleration into high revs where the diesel runs out of puff. The Volvo's acceleration swells beautifully around 3-4k just where the Golf is needing another gear. Translate this into a side by side race, and you can see that the Volvo would pull away convincingly at this point. However, the Golf would have pulled out a lead before this due to the wallop it delivers at low to medium revs. I have never raced the two cars, and I know the Volvo is the faster from a standing start, but you need to work the petrol engine so hard to deliver what the diesel does with a simple flex of the right ankle.
At town speeds, or during stop / start driving where you're spending a lot of time in the bottom half of the rev counter, the diesel simply produces more torque and more power. That is the hard fact of it. I can take the Golf for a blast around the lanes, and simply leave it in 4th. That gives me back-in-the seat acceleration from 35 mph to well over the legal limit. If I need to squirt into a gap, or my favourite activity in the Golf - join a motorway, the on-tap grunt is verging on breathtaking for a small, cheap family hack.
In something like a Caterham or an Elise, which I'm likely to thrash everywhere, or in a big car which I'm not paying the bills on, give me a petrol engine. Otherwise I'm a diesel convert.
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I know the maths but I also know what the seat of my pants tells me.
I'm talking about the truth of the comparison, as indicated by acceleration times. Give me scientific facts, not seat of the pants impressions.
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It's your assertion, M. Escargot; how about you giving us the maths to back it up?
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If I was doing the miles I'd consider a diesel, but I don't so I won't + I'm a dyed in the wool petrol head and don't really like diesels ... I've had a couple - AX 1.4 and a Disco both no prob til I tried to change the fuel filter and got air in the system - the little Citroen was actually a blinder and I drove it to Tenerife & back (via Cadiz) and it never missed a beat, but obviously it was fairly low tech compared to today's oil burners which have almost as much electronics as a petrol job.
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........... how about you giving us the maths to back it up?
The only authoratitive documented evidence that I have to hand of a comparison of similar size engines in a given car with a manual gearbox is from an April 2008 Ford Focus brochure. This gives a 0-62 mph time of 9.2 seconds for a 2 litre petrol producing 145 PS maximum power and 185 Nm maximum torque, and a 0-62 mph time of 9.3 seconds for a 2 litre TDCi diesel producing 136 PS maximum power and 320 Nm maximum torque. Note that although the diesel has a maximum engine output torque of 320 Nm compared to a mere 185 Nm for the petrol the difference doesn't result in better acceleration for the diesel. As I said before, it's torque at the driving wheels that is the relevant parameter and this depends on the overall gearing. The torque at the driving wheels is inversely proportional to the overall gearing ~ quoted in, say, mph per 1000 RPM engine speed ~ and the higher gearing of the diesel is the reason it loses out to the petrol.
At one time there was a magazine which gave acceleration times for conditions other than 0-62 mph but I can't remember what it was or whether it's still available.
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0-60 times for my brother's diesel A5 beat the petrol version by a considerable margin.
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Only motoring journalists do 0-60! In the real world, its rolling acceleration that matters. Autocar and others in their tests list a number of other characteristics, like in-gear acceleration, which are more realistic. They don't depend on brutal techniques that no sane owner would tolerate.
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Is the A5 diesel that much better? Assuming you're comparing like with like, the 2.0 TDi does 7.9/8 sec, 2.0 petrol around 7.8 sec.
Moving up the engine scale, 3,0 diesel, around the 5.7/5.9 secs, 3.2 petrol, 5.9/6.4 secs.
I don't see any A5 figures favouring the diesel "by a considerable margin"
Edited by lordwoody on 08/07/2009 at 11:20
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From the Ford Focus e-brochure:
2.0 petrol: 31mph to 62mph in gear acceleration: 11.9 secs
2.0 Tdci: 31mph to 62mph in gear acceleration: 7.8 secs.
The diesel is four seconds quicker, which in this context is a lot.
0-62mph is about the same, 9.3secs for the diesel, and 9.2secs for the petrol.
Given the importance of in gear, or rolling, acceleration, the diesel is the one to have.
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That's just weird!
2.0 Petrol can do 0-62 in 9.2 secs, but if it is already travelling at 31 mph, it can only do 31-62 in 11.9 secs.
There must be a rational explanation for this.
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That's just weird! 2.0 Petrol can do 0-62 in 9.2 secs but if it is already travelling at 31 mph it can only do 31-62 in 11.9 secs. There must be a rational explanation for this.
Yes 30-60 will be in a given gear, maybe 3rd? Whereas 0-60 will be "thru" the gears.
Edited by TimOrridge on 08/07/2009 at 13:41
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Your explanation sounds logical to me.
In which case, I'd like to see the 31-62 times "through the gears" to mirror real-world driving, then.
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...That's just weird!...
Pretty sure I lifted the figures correctly :)
Something to do with gears used or gearing?
Either way, I think it illustrates why so many people like modern diesels.
As DP said further up the thread, just flex your right ankle and the overtaking grunt is there.
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As DP said further up the thread just flex your right ankle and the overtaking grunt is there.
The "overtaking grunt" is there in my 2 litre petrol as well. And I don't have to suffer all the diesel noise and smell.
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Our S60 D5 feels faster than my previous Leon Cupra petrol, despite similar power and the Leon being lighter (185 bhp v 180 bhp). It's the great fat globs of torque available from the first spin of the turbo! My motorbike, as a total contrast is very peaky, producing about 100bhp but not alot until about 6k rpm. The bike is ultimately an awful lot faster (revs to 12500), but the grin-inducing torque from the D5 always brings on a grin, and makes it very useable in most kinds of traffic.
Re misfuelling, we've not done this, but as the consequences are potentially so bad for a moment's inattention, we bought a fuel angel (google it for more info) for about £30 which means the unleaded nozzle won't fit in the filler any more. Sorted.
If it were me, I'd try examples of both engines types and see which I liked most.
Cheers,
Alex.
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2.0 petrol: 31mph to 62mph in gear acceleration: 11.9 secs 2.0 Tdci: 31mph to 62mph in gear acceleration: 7.8 secs. The diesel is four seconds quicker which in this context is a lot.
That's keeping in one gear ~ probably 4th ~ and who does that? I certainly don't.
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L'escargot,
Just book yourself a test drive in a modern turbo diesel and then come, back to us.
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Just book yourself a test drive in a modern turbo diesel and then come back to us.
Wash your mouth out. I've got too much respect for my Gucci shoes at filling up time!
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Wash your mouth out. I've got too much respect for my Gucci shoes at filling up time!
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But you are prepared to have lubricating oil in your mouth!
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But you are prepared to have lubricating oil in your mouth!
I didn't explain the precise method I used. I attached second (1 metre long) piece of clear PVC tube onto the first piece which had been inserted into the dipstiick tube and which would carry the oil. The second piece was slightly larger in diameter to the first and the two pieces were connected by merely inserting the first piece into the second piece. The fit was good enough to form an airtight seal between the two pieces. I sucked onto the open end of the second piece until the oil reached the end of the first piece. I then separated the two pieces of tube and immeciately lowered the then open end of the first piece into a container to catch the oil which would be siphoned out. The oil didn't come closer than a metre of my mouth so their was no risk of it getting into my mouth. I'm not as green as I'm cabbage looking!
Edited by L'escargot on 09/07/2009 at 08:23
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...That's keeping in one gear ~ probably 4th ~ and who does that? I certainly don't...
Just checked the ebrochure.
It says the figures are in fourth gear - seems they drive both the petrol and diesel the same way for the test.
As regards accelerating hard from 31mph to 62mph in one gear - why not?
I certainly would if it meant for a safer overtake.
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