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Worth paying a premium for a diesel engine?
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Posted 2 years ago #
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Bloke at work has just suggested that I pretend I have kids already and buy a new Berlingo. FFS!! Me, buy a French car?
Besides, it looks fugly.
Posted 2 years ago # -
Well, it's a gutless slug below about 1500rpm
I guess there's something wrong with yours then, mine's fine. Maybe you just don't understand turbo lag?
I hired a petrol Mazda 2 at the weekend. It was incredibly slow, like back to the days of 1.0 Fiesta/Polos, and only got 43mpg. It was totally gutless below 1.5krpm AND above it. You could trundle along nice and smoothly in say 4th at 40mph - put your foot down, and nothing happened. At all. To get onto motorways and such you had to red line it in second.. relaxed capable driving I think not.
My Passat is about twice the size, far quicker, far more versatile and gets more MPG. So why do people like petrol again?
Posted 2 years ago # -
My Passat is about twice the size, far quicker, far more versatile and gets more MPG. So why do people like petrol again?
And costs much more to buy new than a base Mazda 2. What is the equivalent petrol Passat like?Posted 2 years ago # -
Sure, MF - wasn't comparing value. I actually quite liked the Mazda. This is about the engine technology itself.
Posted 2 years ago # -
Here's a dynograph of a Passat 2.0 TDi
Here's one for a Focus 1.6 Petrol
TDi develops about 43kW at 1.5krpm, the petrol about 17kW. About two and a half times the power from the diesel at that speed. TDi develops about 280Nm of torque at the same speed, and the petrol about 105Nm. The TDi reaches pretty much max torque at about 1700rpm, and in normal driving engine speeds it's operating at max torque. Hence torquey driving. The petrol's torque curve is quite interstingly flat all through the rev range but the figures are very much lower than the diesel. Hence having to change down to get it to move much at any kind of speed.
Also note how the TDI's power increases all the way up to its red line.
Posted 2 years ago # -
My mum has a skoda fabia estate 1.9d, gives ugly a bad name but goes as fast as anyone needs a road car to go, handling is precise enough as long as your not driving like a **** and fuel economy seems good.
Posted 2 years ago # -
Going back a bit, me and the Mrs both had MK4 Golfs for a while!
She had 150bhp Gti version, did less miles than me and I had the 1.9tdi 150bhp version as a company car.
(both did not deserve the gti badge tbh).
But the diesel felt the quicker car on the road to drive in real everyday traffic scenarios.
Neither were great drivers cars tbh, but I guess its as close as you can get as a direct comparison to petrol/diesel debate.
Saying that, she was loaned a 180bhp Gti and that was closer, slightly quicker match for the tdi.
Posted 2 years ago # -
I guess there's something wrong with yours then, mine's fine. Maybe you just don't understand turbo lag?
Oh I do. Totally, 100% understand it. And THAT is PRECISELY why I don't like diesels. LAG! **slaps forehead**
I don't care what the numbers and the graphs say, I just care what it feels like when I twitch my right foot. At the end of the day, a petrol engine is more responsive than a turbo diesel. Tweak the throttle, and you get instant action. No matter how much power you get in a diesel, no matter where you are in the rev range, you've gotta send forms in triplicate to the engine when you want power.
There's always that pause as the turbo spools up and the heavy old pistons slowly wind their speed up against that mahoosive compression. That's why, to me, diesel engines don't belong in sporty cars like said Eos.I know I'm in the minority with this, but that suits me fine. I did the maths when we bought our car, and it wasn't worth getting a(nother) diesel financially, so we didn't. And it's lovely to have a smooth, quiet revvy little petrol engine again!
Posted 2 years ago # -
Molgrips, that graph shows the TDI's power falling off sharply before the red-line not increasing all the way.
Posted 2 years ago # -
Molgrips, that graph shows the TDI's power falling off sharply before the red-line not increasing all the way.
Yeah, that feels about right after driving one. 4k rpm and it's all over bar the shouting.
Posted 2 years ago # -
And here's a better comparison to the 2.0TDi VW graphs. A 2.0TSi - Petrol Turbo
Not quite the same headline torque figure, but look at that huuuuge wide plateau of torque! 1700-5000rpm +!
Makes the diesel engine looke like a 2-stroke!
And the power figure murders the diesel. Bye Bye..... See ya, wouldn't wanna be ya!
Posted 2 years ago # -
a different slat, just drove from Cheltenham to Chester via the A5 in my 1.9TDi and got an indicated 73mpg, find me any petrol car that would be remotely comfortable for that journey and give that sort of economy?
Posted 2 years ago # -
mrmo: What kind of speeds were you doing? I don't get anywhere near that in my 1.9tdi on an 80 mile motorway commute.
Posted 2 years ago # -
got 67mpg out of my 1.9 D partner at 70 on the dualer on a round trip without particularly trying to be fuel economic.
your arguement is mute for me PP ill take slow and powerless for that sort of return as long as i can do the speed limit
Posted 2 years ago # -
PeterPoddy - Member
And here's a better comparison to the 2.0TDi VW graphs. A 2.0TSi - Petrol Turbo
Exactly.
My petrol turbo also had a flat torque curve like that. It was fantastic to drive. My TD has a flat spot off tickover, a delay and then a lump of torque which gives a bit of shove, promises a lot ...and then fails to deliver as it dies off fairly quickly.
At ~2000rpm in high gears it does pull quite well. 80-100mph (where conditions allow) is quite quick probably as it stays in the 'powerband' for longer in higher gear, but at medium speeds on back roads it's not that quick.
I'd much prefer a non-turbo 3.0 V6 petrol, but the fuel costs are prohibitive. I'll stick to a tractor for now(and re-consider the petrol/diesel issue when I look to swap) and the purity of a motorbike, which is much more fun.
Posted 2 years ago # -
most of the M5 is 50limits now, then the bit around birmingham to the M54 more 50mph if lucky, more like 40mph, then 60 something on the dual carriageway sections.
I was traveling on the slow side, 60 something rather 70 something it just gives me something to think about on the commute.
Posted 2 years ago # -
Turbo petrols are good for driving, I agree. I thought this was a discussion about NA petrols which are the most common incarnation. I have said on other threads before how I like turbo petrols.
I just care what it feels like when I twitch my right foot
That's my point really - your right foot doesn't know what it's doing.
no matter where you are in the rev range, you've gotta send forms in triplicate to the engine when you want power
Kind of proves my point - you're kind of wrong there. If you are driving over a certain speed the turbo will always be spinning. I can get plenty of instant power from my engine just by keeping the revs up. That's what the S mode on the auto box does, in fat. And it's not fair to say that there's no power under 1.5krpm when the delay is caused by turbo lag not power flat spots. In a NA petrol (unless it's huge) you'll never go anywhere quickly from 1.5krpm ever, whereas by understanding the engine in a TDi you can take off.
And here's a better comparison to the 2.0TDi VW graphs. A 2.0TSi - Petrol Turbo
Do turbo petrols not have lag?
And anyway, why are you worried about the number of rpm? In say a Honda 2.2 CDTi if you just painted over the numbers on the tach with petrol ones you'd NEVER know the difference between it and a turbo petrol.
Molgrips, that graph shows the TDI's power falling off sharply before the red-line not increasing all the way.
That's the limiter. It does tail off *just* fractionally below the actual red line painted on the tach but so what? I was attempting to compare it to the older PD engines which are the ones with a big slug uner 3krpm then a long gradual tail which really is frustrating to drive with when you are trying to say overtake. But again, plenty of fun can be had if you aren't an idiot.
You seem somewhat obsessed with one specific driving style, and with some numbers. You seem to feel that unless the tach needle touches a 6 you haven't achieved something, regardless of how the engine's performed up til that point. Diesels can be just as fun and sporty if you aren't a complete numpty with the throttle..
Only diesel disadvantages in my view (and experience) are:
More NOx/particlulate pollution
Heavier engine may affect handling if you are really into it
Higher cost
Increased energy cost in refining possibly.Posted 2 years ago # -
So the limiter starts to kick in at 4000rpm yet the engine continues to rev to 4500. That's nearly 15% of the rev range. This is not caused by a limiter, but due to turbo constraints. Volkswagen have chosen a turbo that spools early but cannot flow enough air at above 4000rpm, and rightly so.
A petrol turbo will have lag, all turbos have lag. This means that you cannot get instant power. The lack of power below 1500rpm is not due to lag, but due to being below the turbo spool point. Lag and spool are different.
I can see an argument for Turbo Diesels, they provide acceptable performance with good economy. However, I would still spend my money on a larger capacity petrol engine with far better throttle response than either a turbo diesel or turbo petrol. If I were to do more miles I may consider a diesel, but I find petrol engines both more relaxing and more enjoyable to drive.
Posted 2 years ago # -
Not sure you are right about that, Harmitans. The car I fiddled with most was a 1.9 TD IDI all mechanical engine. The limiter was a compound spring arrangement that was set up to gradually reduce fuelling as you approached the red line. One of the favourite mods was to remove the softer of the two springs so that it kept on pulling. Only problem then was that it felt like hitting a wall as you hit the limiter. I think that maybe that's why VW didn't set it up like that. It was also possible incidentally to mod the springs further and get 5.5krpm or so out of the engine.
But what's in a number? Why is 4,000 worse than 6,000 if the gears are longer, so it gets you from say 30-70 in the same time, and if the output curve rises in a similar way?
A big petrol engine could well be lovely to drive.. but they drink fuel. If you care nothing for efficiency, waste, pollution etc etc then knock yourself out.
To me, efficiency is a fundamental engineering principle, so a car that does 25-30mpg is just wrong.
Posted 2 years ago # -
molgrips , a man after my own heart !
a car is a tool not a toy
Posted 2 years ago # -
Unless you are at a track day, in which case I doubt I'd take a diesel. But then I might, just to make a point
Posted 2 years ago # -
not sure why some people find petorls more relaxing to drive. For me a diesel is much more relaxing (for everyday driving) as theres not as much changing down for overtaking. Mine just cruises along at about 1700rpm and i put foot down and it accelerates straight away. Same with all the modern diesels i've driven recently from Hyundai / Kia 1.6, ford 1.6, VAG 1.6 and 2.0 engines (all diesels).
I found the petrols i've driven recently much more hard work to be enjoyable with having to get the revs higher for any power.
Also super economy on modern diesles amd often lower tax (£35 on the kia and ford ones which were also very good to drive)
Posted 2 years ago # -
I could well be wrong about the limiter, my experience with turbo diesels is based on much larger engines.
Do you have any figures for these modded engines, e.g. dyno charts? I suspect removing the spring will slow down the decrease of torque but it will still be decreasing. Do the diesels that rev to 5500rpm still use the standard turbo? I'm really interested to see how much torque they're producing at those revs.
The problem with 70mph at 4000rpm in a diesel compared to 6000rpm in a petrol is that at 1500rpm in my petrol I have 84% of peak torque available, yet in the diesel you are now at 1000rpm. In the Audi 2.0TDI I drive for work, this means one of 2 things either change down or wait and wait for the turbo to spool then get a big lump of torque. I prefer my car.
My 3.0 petrol engine returns between 30-35mpg. I happily pay for the extra fuel not to drive a diesel.
Posted 2 years ago # -
Hmm interesting point about the need to shift down in a petrol ot overtake, my midget sits at 3k rpm in 4th on the motorway at 60*. Fraction more throttle and it shoots upto 70 for overtaking.
*indicated speed, my parents follow in the focus sometimes and we recon the spedo is bang on, morden cars (i.e. someone hasnt calibrated each speedo individualy) seem to over read by 10%.
If it wasn't for the complete lack of noise insulation (and dire need for another 20hp at arround 3k rpm, 500rpm on the redline and another gear) it makes quite a nice motorway cruiser.
Posted 2 years ago # -
Do the diesels that rev to 5500rpm still use the standard turbo? I'm really interested to see how much torque they're producing at those revs
Not standard turbo.. not standard anything apart from the block
There is amazingly a really healthy TD and TDi modding scene in the US and Canada...Harmitans - not sure what you are trying to say there. You may be at a high percentage of peak torque at 1.5krpm in a petrol but from a diesel driver's point of view that's 85% of bugger all. I can get more torque at the same revs in a diesel, then when the revs are higher I get even more.
Diesels have loads more torque than petrol - fact. They also have more power at lower revs. To me that means you can drive more at lower revs, which means a relaxing drive. Having to drop through the gears to get the car moving means extra bother imo.
Posted 2 years ago # -
What I'm trying to say is that I have to change gear less in my petrol car than I do in the diesels I drive.
Whilst a diesel engine has a higher peak torque, the gearbox has to have higher gear ratios due to the lower engine speeds. This results in less torque at the wheels which is what actually accelerates the car. A petrol car has higher wheel torque than a diesel at low rpm and high rpm.
The diesel only has greater wheel torque in the mid range. To me this feels like a narrow power band and hence more gearbox stirring.
Posted 2 years ago # -
Only if you want to sound look a taxi, smell like a chip shop and look like a cheapskate.
Posted 2 years ago # -
I can't imagine how on earth you drive harmitans. I have always had to change gear more in petrols. Only yesterday I was driving a Mazda 2 petrol. I'd be cruising nice and smoothly at 40mph in top gear; put my foot down and absolutely nothing happened. I'd need third to get moving. In a comparable diesel such as the Seat Ibiza I used to drive, you could be away in 5th at 40mph, and quite quickly too.
So I can't imagine what on earth you are talking about. As for wheel torque - in most diesels I've driven the ratios are maybe 50% longer than in petrol in cruising gears, and the difference is less in lower gears. Torque levels are around 2-3 times as much. So there should still be more wheel torque.
Just checked back to those graphs I posted, and I think the torque curves are wheel torque, which kind of proves me right.
I don't think a 3.0l petrol is in the same class of car as a 2.0 TDi anyway, so comparisons of that nature are moot.
Posted 2 years ago # -
I'm off home now. I reckon I can get the 11 miles home with 23 gear changes. In the diesel I think it would take 37.
The graphs are wheel torque/total reduction versus engine speed. If you re-scaled the graphs so that all the cars were in a gear ratio that allowed them to travel at the same speed at max rpm the 3.0 petrol has more wheel torque than the 2.0TDI through the whole rev range as does the 2.0T VAG petrol. The 2.0 VAG petrol has more wheel torque only at low and high engine rpms.
Posted 2 years ago # -
I agree that a 3.0 petrol and 2.0 turbo petrol will have more torque, of course they will. They are sportier engines in a more expensive class of car. The 2.0 TDi in the Passat is a ubiquitous workhorse engine and not very expensive to buy or run.
If you want to play torque top trumps, I give you the VW Touareg 5.0l V10 TDi with 590ft/lbs or 890Nm at 2krpm. That's over double the torque of the V6 petrol and at lower revs (3.0L V6 265 ft/lbs at 2.5krpm). The TDi is also more powerful and significantly faster, with a 0-62 time of 6.7s versus 8.4s for the petrol. Fuel economy is the same.
You're talking through your arse mate. Comparing like for like, diesel is more versatile and more efficient to boot (edit) than NA petrol.
EDIT again:
If you re-scaled the graphs so that all the cars were in a gear ratio that allowed them to travel at the same speed at max rpm
Wtf? Is that how you drive?
Posted 2 years ago # -
You seem to be contradicting yourself so I wont say any more.
However, I will play top trumps:
Mercedes 6.0 V12 Turbo - 1000Nm. Petrol rules!
Posted 2 years ago # -
**** me they are tin boxes, with wheels, you move along roads in them as long as they go, dont cost a fortune and can cruise along at 75-80 why exactly does it matter.....
Posted 2 years ago # -
I bought my diesel 2nd hand. Granted I could've got a newer / better specced petrol for the same money, but servicing costs seem the same and apart from 18 months ago the price difference between diesel and petrol means it works out better value - a full tank goes a bit further for only a bit more.
I think paying closer to full price I'd probably consider a petrol with stop-start technology. The BMW 116 gets something like 48mpg out of a petrol IIRC.
Posted 2 years ago # -
Whats driven the leaps in diesle performace? Is it trickle down technology from truck engines or the demand for more fuel efficient cars that drive more like petrols?
I sometimes think that whatever you buy (petrol / diesel / hybrid) you pay the same in one way or another either by price of petrol /servicing / initial cost / repairs. Its all a very clever conspiracy by the chancellor / car companies / garage cartels and oil companies - they're all controlled by the 7ft lizards!
Posted 2 years ago #
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