>>I thinkit's high time that car manufacturers quoted both engine torque and torque at the wheels ~ preferably in all gears.
And before someone takes me up on this, I'd better add ...."Except reverse, of course !!"
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Yes, you are right -
The massive torque of the modern TD,
(plus it's lower rev range than a petrol)
does mean the TD gearing is MUCH higher.
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Unlike petrol, diesel oil when compressed combusts slower and with a greater expansion ratio that ignited petrol. This produced a greater pressure on the pistion for a longer period thus more torque. However, due to the slower action og the diesel they can not rev as high as the burn rate is the controlling factor. Hope that helps. Regards Peter
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I think it's more to do wth turbo-charging than innate differences, in terms of the amount of torque. Normally aspirated engines produce much the same torque, although diesels produce it more effectively at low rpm. Turbo charged petrol engines have equally high torque figures, probably over a wider rev band than diesel. However, diesel allows higher gearing, and the use of the power more often in the real world, because mpg is greater:)
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Quite right, Peter - and the pressure is known as the Break Mean Effective Pressure (BMEP).
Ian Cook
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Or should that be Brake (not break) Mean Effective Pressure?
Ian Cook
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"TD gearing is MUCH higher"
..which rather defeats the object, surely? Give me a smooth, flexible petrol engine every time.
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A good turbo petrol (such as Audi's 150bhp 1.8T) will have bags of torque and will have most if it over a huge rev range - unlike the narrow band that most TDs insist you drive in.
I have both turbo petrol and turbo diesel cars. Give me the petrol any day - less noise, much cheaper to service, and a damned sight nicer to drive. The huge extra cost of most turbodiesels means you have to drive about a zillion miles before the hugely exaggerated fuel savings kick in.
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The huge extra cost of most turbodiesels ...
This might be a daft question, but AIUI a diesel engine is less complex than a petrol, especially as a lot of petrol engines these days features loads of electronic gizmos. Why, then, are diesel cars so much more expensive than petrols? I can see it for the top end where you'd need more robust gearboxes and clutches to handle the extra power, but surely on the basic ones you could use the standard components?
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you have to drive about a zillion miles before the hugely exaggerated fuel savings kick in.
My personal experience with a petrol turbo and a diesel turbo (both 2-litre) driven over exactly the same route in the same style over 1-2 years each, gave a fuel comparison of ca. 37 mpg for petrol, about 56 mpg for diesel (i.e. the petrol car used ca. 50% more).
My 12-month fuel cost for the petrol car was £2,400, so the diesel car saved a not insignificant £800-odd per year. The actual bills confirm this. (It was actually more like £950).
I drive 36 miles each way to work and motorway is a large proportion (i.e. well short of a zillion miles). :-)
Oz (as was)
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How about compression ratio? That must surely come into the picture. 20:1 (ish) for a diesel and 10:1 (ish) for a petrol.
Steve.
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If you take a Focus Tdci you will get 44-46mpg in normal running. A Focus 2.0 will give 36-40. We have just run two Ghias over 20,000 miles each and have the first hand evidence. At list prices the Tdci cost almost £1800 more. That's a lot of diesel.
The Tdci gets serviced every 10,000 miles (and needs the oil topped up very frequently). The petrol gets serviced every 12500. The petrol costs £95 to service, the diesel £120.
We also get 36mpg average and 40mpg in hard cruising out of an Audi A6 1.8T. It's a no brainer which car to use.
Then factor in the NVH.... you simply don't want it in decent cars.
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Yes Shigg Compression ratio comes in to it but it is due to the fact that diesel fuel only combusts when the pressure exceeds about 16 bar 16:1 compression ration. Peter
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Fergus, you may have a petrol driving style, which means the petrol cars suit you more.
Your economy for the 2.0 Focus and the A6 is above what what could be expected for these so you probably have quite an efficient driving style or use a lot of motorways.
However, in these conditions, surely the Focus should give 50+ mpg. If the TDCi's used image holds up, a large chunk of the price difference against the 2.0 could be maintained after a couple of years.
I had 90bhp Peugeot 405 TD (46mpg) before my current 100bhp Fiesta (37 mpg), but found the Fiesta's performance poor to begin with. If I went back to a diesel it would take me a while to adjust.
A friend with a Rover 200 TD tried an MG ZR 105, which had similar stats on paper, but found the MG to be gutless (since the performance comes further up the rev range). However, the 200's engine is a tad too agricultural for my liking.
James
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"Then factor in the NVH.... you simply don't want it in decent cars."
Quite agree. No matter what the saving, I simply don't want to drive something agricultural. The last time I posted such sentiments here, I was told that I hadn't tried certain Mercedes/BMW diesels (which was true, and likely to remain so) but then that rather blows the economy argument out of the water.
I prefer petrol for all sorts of reasons, but I don't mind too much if others like diesel - just as long as they don't try too hard to convert me and don't spill too much of the stuff on the road when I'm on my motorbike!
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Fergus -
Absolutely right - no brainer.
I use regularly both petrol (Audi TT 225bhp - 27mpg) and diesel (Skoda Fabia 100 bhp - 55 mpg).
The petrol DOUBLES my overtake opportunities on the windy 60 limit road - from average of 1 per day to 2.
As you say - no brainer.
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So TP a 225bhp petrol sports car is faster than a 100bhp family diesel...you don't say.
And if you need the extra 125bhp to gain just one overtake on a journey then it sounds as if you are driving much like Ben Chapman.
But of course you were just joking???
MM
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MM -
"it sounds as if you are driving much like Ben Chapman"
OR the number of SAFE overtakes the 20% extra torque gives you
(on our crowded roads) is not enormous.
(yes 20% - from 173 up to 206)
Yes, of COURSE I was just joking (not)
I ALWAYS joke about driving.
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NVH?
Regards
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My point about compression ratios being thermal efficiency and BMEP on the piston........
Steve.
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NVH?
Noise / Vibration / Harshness
I agree - I test drove both 2.2 diesel and 2.2 petrol Vectras - both 'new' engines in the old model. Both were fast, and I could appreciate the increased torque in the diesel. What was the biggest letdown however was the increased noise and vibration through the wheel and gearstick in the diesel. I wasn't going to be convinced that the old model Vectra would survive for long-term ownership without important bits coming loose / falling off. The petrol version felt altogether more 'sophisticated' if that and 'Vectra' can go together.
Steve
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Here's a no brainer for you: the manufacturer's power/torque/noise level stats for the Peugeot Partner Combi, one of which I just bought. Not the quietest car on earth, but:
1.6 16v Petrol: 110bhp@5800rpm/110lbft torque@4000rpm/71.2dB(A), moving.
2.0 Hdi Diesel: 90bhp@4000rpm/154lbft torque@1900rpm/71.2db(A), moving.
So we see that the diesel produces maximum power and especially torque at more useable revs (1900rpm is about 55mph in 5th gear) and the noise levels are...the same. Mixed cycle fuel figures are: 38.2mpg (petrol) and 49.6mpg (diesel)--the latter is working out about right so I don't doubt the former. New prices are within a few hundred pounds, but the petrol will no doubt depreciate quicker.
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Interesting data Chris. I have no doubt that the petrol fans will STILL argue that diesel noise, whilst the same absolute level is a harsher kind of noise, and offends their ears. I think the point about NVH is that they (petrol fans) go looking for it in a diesel and imagine it is much worse than it really is - the reverse of the placebo effect? They also always seem to say "the diesel is £x more expensive, so takes y miles to pay off" - usually forgetting the the diesel will usually be worth at least the original difference more than the petrol after about 3 years.
I find it hard to drive petrol cars now - I wonder why they won't pull from under 2000 rpm, why I need to keep dropping down gears, why I can't manoeuver them without using the throttle, and why I stall them 3 times before I even get out of the carpark!
Having said that, I hanker after a Xantia Activa which only comes with the 2l petrol turbo "Constant torque" engine. I imagine this will be much the same as a TD to drive, but with a wider rev range (and 25mpg...). Of course I could always pull that out and drop a chipped HDi in (135 BHP!) which would eat the 150BHP petrol for breakfast in in-gear performance, flexibility and fuel consumption.
Richard W
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"71.2db(A)"
That's inside the car, I take it...
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I'm assuming so, but really these engines are quiet even at cold tickover with the bonnet up. No noisier than a petrol with a dodgy water pump. Certainly not the blacksmiths' convention of old.
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Wooh - prompt reply! I bet it will rattle in a year or two, but having said that, it probably suits the vehicle well (I'm not being rude - I like the Partner and Berlingo). HJ seems to think that the C3 diesel is a marriage made in heaven, too, so I'd better reserve judgement...
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Here's another prompt one.
No offence taken. If I'd wanted a 1.6 "screamer" I'd have bought one. And yes, it probably will rattle, but it won't be the engine that causes it : Mmmm. Smooooth. No, it will be the stuff we chuck in it that will knock chunks out of the trim over the next 5-7 years. You are underrating this design of engine something rotten.
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