I am fairly new to diesel, having got a Seat Alhambra TDi a couple of months ago, and have had time to consider the characteristics of the engine.
The good
Effortless cruising and overtaking
Blinding economy
The bad
Urban driving.
Before I got a diesel I was led to understand that the huge torque pulled you in pretty much any gear. Where we live is heavy on roundabouts, and it seems pretty easy to get stuck in a the wrong gear with no power. I also have an old 115bhp BMW 318 petrol which will hit a roundabout in 4th gear with not much more than 1000rpm and still pull away ok. The diesel is left powerless and needs a gear or two dropped. Basically I seem to change gear a lot in the diesel when urban, which is not what I expected. I suspect part of the problem is generally tall gearing, although the engine seems to have a power dead spot below 1500rpm before the turbo kicks in. Is this the usual diesel experience? Still love the car though
David
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In my Vectra GSi Estate, I often roll up to roundabouts in third gear, clutch engaged, revs dropped to five or six hundred, judge the gap, and go. Easily.
Borrowed a colleagues new 320d earlier in the year, and was impressed with the mid range torque.
However, he nearly had it returned in kit form: Doing my normal Vectra trick in his car, I found myself havng rolled on to the roundabout, at walking pace, foot welded to the floor, no acceleration AT ALL, and fast traffic bearing down on me.
So much for Diesel torque.
I would have thought that a three zillion to one compression ratio would have made it pull like a steam engine, even without any turbo boost, but obviously, not!
/Steve
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I think at low revs the 'bang' in the combustion chamber simply is too small to deliver any torque. I guess thats why they put turbos on them, even though this will not help at low revs. The new turbo diesels are very 'torquey' but i don't think they will pull from idle like a v6 petrol engine.
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Hmm, curious. My experience of diesel (mostly old 1.9 non-turbo) is that it's fantastic in town - almost like driving an automatic in that you can leave it in third and cover just about anything (at a pinch) but a full stop. In fact it's unhappy over 3000 revs. However, I've recently been test driving brand new HDI turbo diesels and these are less torquey at very low revs. But when maximum torque on the HDI 90 comes up at 1900 revs, and it's almost double what the 1.6 petrol manages at 4000 revs (IIRC), I'd hardly say it was a major problem. Must be the turbo setting on your VAG diesel.
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Just to add, the Alhambra is a huge car, and must be much heavier than a 3-series BMW. Maybe that's contributing to what you see as a lack of performance, especially with a 1.9 (?) engine. Must be very reliant on that turbo.
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Hmm, curious. My experience of diesel (mostly old 1.9 non-turbo) is that it's fantastic in town - almost like driving an automatic in that you can leave it in third and cover just about anything (at a pinch) but a full stop.
I know what you mean, Chris. I have a Citroen C15D van with a 1.8 non turbo diesel and it's superb around town. Pull away in second, slip it into third - and then into fifth. Goes round most street corners in fourth quite happily.
It's also quite happy at 70mph, a little noisy - but then it is a tin shed.
SWMBO's Xantia HDi is quite different. A fair bit of torque from about 1250rpm but generally more petrol like. Quieter and a lot higher geared too.
Petrol? It'll never catch on, will it?
;o)
Ian Cook
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If by "it seems pretty easy to get stuck in the wrong gear"
you mean it will not tolerate the abuse of driving round roundabouts in 4th gear,
you are probably correct.
Yes "part of the problem is generally tall gearing"
As others have pointed out, modern TD's have practically nothing below 1500 - so don't go there.
(try 3rd gear 30-60 and 4th gear 40-80)
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Hi David
I've recently bought a Citroen C5 (2.2 HDI - Turbo - with particle filter) I can't say I've had any problems whatsoever at low speeds. I can dribble the car along very easily in traffic, yet it goes like stink when you floor the throttle. It puts the power down very evenly, without any lag or noticeable flat spots. Can't say I've noticed any downsides, or even had occasion to look at rev characteristics. Strange to say, I find it has all the benefits of my previous car (Xantia 1.8 petrol) with the addition of much more get up and go and far less noise! (I know, you'd expect the opposite!)
This is my first diesel - can't imagine now why anybody would want a petrol!
Graeme
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I always thought that it was bad for a car to try and apply any power at low revs. Mine certainly puts clouds of smoke out for others to wade through when SWMBO (ok, and me too) forgets to change gear…
When I hear people talk the torque (Agghhhh!!!) I always assume they mean mid-range acceleration – ie not having to change down to pass a vehicle in front.
Splodgeface
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I would list urban driving as one of the strong points in my non-turbo Octavia SDi, I never touch the throttle when pulling away from rest until the clutch is completely home. The torque at idle is enough to get the car moving without any throttle at all, pretty much as long as you don't sidestep the clutch pedal! I'm hoping this should make the clutch last longer, as the differential of speed between the 2 clutch plates should never be much more than 1,000 rpm.
As I mentioned in another thread last week, I found a Vectra 2.0DTi to be very petrol-like in its power delivery, most probably to appease company car drivers who have no choice in what vehicle they get, but who don't (or won't) adapt their driving style to suit a diesel.
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From a completely non-expert's view, I find that there is far less need to change gear on my diesel car, it can do most things in 4th and I can change it to 4th a lot sooner than I could with any petrol car. (last petrol car couldn't get into 4th until well over 30mph, diesel is quite happy to be in 4th after maybe 20 mph.
Having said that, I have only been familiar with 3 petrol cars in all of my driving experience.
But the diesel's pretty amazing. I like it. Most wouldn't, maybe, but it's great for me.
HF
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I just love the muscular feel of diesels. A few weeks ago I went up Telegraph Hill near Exeter in my A4 TDi, four up, luggage, long, steep hill, but it went up easily in 5th (top) gear. In previous cars (inc 6 cylinder 320i) I've had to go down to third and made slower progress.
And I still get 50mpg minimum!
Regards
Pat
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I had an Audi A4 TDI (110) - same engine as the SEAT but maybe yours is a 115 or a 130?
Anyway, would pull from 1000 rpm in 4th but obviously little acceleartion.. but at 25mph in 3rd about 1400rpm it went very quickly. Turbo kicked in at about 1500rpm and it jsut kept acclerating.
I would imagine the SEAT is probably 0.5tonnes or 30-50% heavier so the poor thing is both highly geared and much heavier..
(MPVs are not cars and are not designed to be driven but steered like boats so any attempt to drive them like cars is doomed to failure from the start. Well.. at least that's my opinion... as for 4x4s...well I'm sorry so many urban dwellers drive so badly in town they keep being worried about going offroad:-)
madf
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Madf and David R
My Audi A4 is the 115PD and I love the power delivery, even though I'm not really a speed merchant. As it happens, I also have a BMW 318i 115 BHP (S reg touring which my wife uses mainly) and by comparison it feels weedy, underpowered and low geared (70 mph in 5th is 3400 rpm compared with 2300 in the A4. Nice car to drive but I keep saying (ad nauseum, apperently) to SWMBO that it would be a superb car with a diesel engine like the Audi's.
Strangely enough, it's only now that I've realised that both cars have the same bhp, but the Audi feels far more powerful - I rarely risk overtaking on A roads in the beemer because it just doesn't pull strongly enough. SWMBO is more than happy with it, as am I in most respects.
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Pat L
I know where you are coming from with the 318s gearing, always find myself reaching for a higher gear at 70, then find there isn't one! Still more flexible than the bus's diesel in town though, although there is a big difference in mass. I thought the beemer's A road overtaking problem was sorted by dropping a gear, works for me. And whoever said MPVs don't drive like cars, shame on you!
David
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Difference between turbo and non-turbo engine (dieessial or petrol) : compression.
High compression/non turbo = high bmep at most revs (valve overlap/timing, exhaust scavenging and induction resonance also relevant) = pull from low revs. Now bolt a turbocharger on without reducing compression ratio, still high bmep = pull from low revs. Turbo spins up, boost pressure increases = more power (due to compression ratio increase); higher revs = more boost = further increase in compression ratio = more power etc but eventually .... BANG, catastrophic engine failure. Solution: reduce calculated compression ratio (no boost from turbo) to ensure reasonable engine life at max turbo boost.
Deisssals have higher peak torque at lower revs compared with "equivalent" petrol engine. Petrol engine typically has wider rev range of usable power. Oddly enough, 2 stroke motorbike engines (supposedly peaky) can have a wider usable rev range than 4 stroke petrol/disseal car engines. My trusty RD350 (many years ago now) would pull from 3000 rpm to 12000 rpm = 9000 rpm of usuable power, turbo disseallll car = 3000 rpm of usable power(?)
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Micky, I like your different spelling of diseasels. Keep'em coming!
My son has a naturally aspirated Clio diesel and this is certainly more flexible than the various small turbo diesels that I have driven.
He is close to buying a Skoda Fabia Sdi (about 18 secs 0-60) and I thought he should go for the Tdi (11 secs or less?). Now it has dawned on me how pleasant the Sdi is to drive in town, and how much quieter it is than the Tdi, and I'm beginning to support his choice.
He says that there is hardly anywhere you can make full use of fast cars nowadays so why pay more for a turbo? Perhaps he's right.
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Or, to put it another way, the in-gear acceleration bit is FAR better in the turbo, and the overall fuel consumption is the same.
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But over the life of the car, the extra stress put on the drivetrain by the more powerful turbo engine will lead to more drivetrain and suspension failures. I find turbodiesels tend to eat wheel bearings, CV joints, ball joints and suspension bushes far more quickly than non-turbo diesels. If the extra power is there, you're going to use it, aren't you?
Mondeo 1.8TD eats front suspension components in 50-70,000 miles.
Peugeot 405 1.9TD ditto 70-90,000 miles.
Cavalier 1.7TD ditto 60-70,000 miles.
Cavalier 1.7D - 280,000 miles, been through all drivetrain components only once.
Skoda Octavia SDi - nothing yet, 127,000 miles so far.
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I had a similar problem with my passat 1.6td (80 bhp). When dropping clutch and setting off at roundabouts the initial power delivery was a big problem - nothing happened until you hit 2000 rpm, then all the power suddenly stormed in, which in wet weather used to spin the wheels - ie NOT GOOD.
Once on the move it was much better the mid range tourque being very good (for a 1990's diesel) appart from a lot of boom a continental driving speed (85mph).
When you think about it until you hit 2000 rpm this heavy car/bus! would have effectively had a normally aspirated 1.6 deisel with restricyed airflow! - no wonder it felt slow.
Well if you scale this up to an even larger Seat Alhambra, before you hit 1500 rpm you are again effectively running a sub-normally aspirated 1.9 diesel. The base engine should be larger as in the Citroen 2.2HDI... I bet these dont have the same problem.
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It's because the turbo isn't spinning, simple as that. below about 2000rpm, there'll be no boost from the turbo, so no power.
You don't get this in a non-turbo car, as, well, there's no turbo. However, you also don't get the massive punch from the turbo either.
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Hi, I've driven diesel vehicles since passing my test 14 years ago (Mk.1 Astra's), as far as I can see some people hate diesels purely because they're not petrol and don't behave the same. Both pretty obvious really, a bit like men moaning about women and vice versa. If the majority of people are prepared to listen to the likes of Jeremy Clarkson et al. then leave them to it. Those in the know don't. Just to really stir it up, am I alone in wondering why all the 'motoring' T.V. shows only care about how fast, how much power, etc?
Steve.
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Steve, you're not alone!
I am fascinated with most aspects of motoring and have had my share of fast cars over the years. However I detest the idiotic tyre-burning antics and sensationalist 'reporting' that has blighted TV motoring programmes in recent years and I don't watch any of them now.
Slight correction -- I have taken a look at Driven and the Clarkson programmes a couple of times recently but have switched off after five minutes or so of the drivel.
It is obvious from comments made in this forum that Clarkson et al have some enthusiastic supporters. I find that very sad.
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Well I guess that come the next fuel crisis, a la 1970s, all the drivers of these underpowered (underpowered for what?) 2.0ltr petrol monsters will be moaning. Good luck to them, I'll still (hopefully) be running my little 115 that gives 50 mpg around town. Don't get me wrong I'm no angel when it comes to enviromental issues but my attitude is that just because you can afford something you shouldn't waste it. How many of these people go to work and leave the taps running, have their central heating boiler swapped for something that uses more gas or strip out the loft insulation so they can store more in their lofts? Maybe the same people that moan about the middle east problems should think a little deeper.
Just going back to the Driven (Drivel?), Top Gear (Reverse?) thing, my brother mused about the success a TV version of Autoexpress could have. Any thoughts?
Steve.
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I'm with you, Dizzy. Of the overgrown adolescent mob on Driven etc., I think the bikers are the worst. Come back Quentin, all is forgiven!
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I can't agree with the bikers part, I've got a bike and a twist & go. But some of the people that ride bikes are stupid, funnily enough the worst seem to be the ones who own a bike as a fair weather toy. I think that generally people who ride in all weather have real appreciation of the dangers of speed, road conditions, etc.
Steve.
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