4-Cylinder Petrol or 6-Cylinder Diesel
Discussion
surveyor said:
Modern Petrol engines are becoming just as complicated as diesels with Turbo's etc.
Except that the DMF's last the life of the vehicle in a petrol car (against 60-80k), even injectors on Petrol DI engines aren't a fortune (although that's just for the parts and non-BMW cars 
). Turbo's, yes I'll grant you that. Plus they don't have a DPF.If a modern diesel is running perfectly well and nothing breaks it *will* still need a new DMF. Sometimes after as little as 60k (with a few abnormal replacements earlier). It's a service item now and the cost of that can wipe out a significant amount of saving on fuel.
Oh and for Max_Torque, I have a Mondeo 2.5T, if you compare it to the 2.0 TDCi which has the same 320Nm of torque the Diesel produces it between 1750 and 2240rpm. The Petrol 2.5T? 1500 to 4800. Plus the Diesel is slower (top and 0-60), heavier and costs more to service.
As to BMW, sorry to bring proof into the mix rather than make sh*t up but lets have a look at the real examples here
328i
330d
Hmm, is that a 1250-4800rpm spread for the petrol and only 1700-3000 for the diesel?
Oh yes it is. So peak over limit gives 26% for the Diesel and 50% for the Petrol and with only 2k more to play with the gearing isn't going to be so wildly different to make up for that.
So to repeat myself, Diesels have a tiny but massive torque spread *requiring* either an auto-box or frantic gearchanges. They don't stick 15+ speed gearboxes on trucks for sh*ts and giggles you know.
Well, what can i say, i bow to your superior knowledge.............
Except, these days, anyone can go to google images, get a picture, post it up and claim that as definitive evidence to "prove" whatever point they were trying to make. Unfortunately, the number of people who have the mental accurity to actually understand and process that easily gathered information is much smaller.
To make this point i have taken your torque curves and converted them to tractive effort plots, which show torque at the wheels for each car plotted verses speed:
As you can see, there is no requirement for the diesel driver to change gear anymore than the gasoline verisons driver
Infact, the opposite is true , and the higher BMEP of the diesel more than offsets the reduction (numerically) in final drive ratio, hence the diesel actually outperforms the gasoline car at all roadspeeds (hence it manages 5.6s to 62mph, vs 5.9). Add in the Co2 advantage (135g/km vs 147g/km) and it is very simple to see why lots and lots of people buy the diesel version!
So, to repeat myself, the "diesels need to change gear all the time" is a fallacy , propogated by people who don't fully understand the relationship between tractive effort and flywheel torque. Luckily for us, the manufacturers, and the people like me who develop their cars do have this appreciation.
;-)
Except, these days, anyone can go to google images, get a picture, post it up and claim that as definitive evidence to "prove" whatever point they were trying to make. Unfortunately, the number of people who have the mental accurity to actually understand and process that easily gathered information is much smaller.
To make this point i have taken your torque curves and converted them to tractive effort plots, which show torque at the wheels for each car plotted verses speed:
As you can see, there is no requirement for the diesel driver to change gear anymore than the gasoline verisons driver
Infact, the opposite is true , and the higher BMEP of the diesel more than offsets the reduction (numerically) in final drive ratio, hence the diesel actually outperforms the gasoline car at all roadspeeds (hence it manages 5.6s to 62mph, vs 5.9). Add in the Co2 advantage (135g/km vs 147g/km) and it is very simple to see why lots and lots of people buy the diesel version!
So, to repeat myself, the "diesels need to change gear all the time" is a fallacy , propogated by people who don't fully understand the relationship between tractive effort and flywheel torque. Luckily for us, the manufacturers, and the people like me who develop their cars do have this appreciation.
;-)
Edited by anonymous-user on Sunday 28th April 01:28
va1o said:
Different end of the scale but I found the same with a 12-plate Astra the other day, horribly rough and unrefined. Felt like a step back to the 1990s and not up to the standard of so called modem diesels.
That got me thinking is it a result of the ever ridiculous emissions requirements meaning diesels are now going backwards in refinement?
As in, the new shape Astra? If you think that's rough you should try the mk5 Astra diesels! The new Astra diesels go some way to fixing the inherent 'diesel flaws' of the old cars. Notably...That got me thinking is it a result of the ever ridiculous emissions requirements meaning diesels are now going backwards in refinement?
- The throttle response is much improved. The mk5 throttle was like mush, and extremely lazy. The new Astra's throttle is much sharper. It wouldn't pass muster against a good petrol, but it eclipses the old effort.
- Turbo lag is considerably decreased. The mk5 was littered with flat spots. The new Astra's turbo seems much more perky, and gone are the yawning gaps in power delivery. The mk5's second gear was absolutely horrendous beneath 3000rpm on a flat surface, never mind uphill. Save for a slightly short 3rd gear in the new Astra 6 speed, it's better.
- The engine is quieter at idle. It still sounds rough, but the insistent, loud 'clackclackclacklacklack' of the mk5 is much better disguised now.
Max_Torque said:
Well, what can i say, i bow to your superior knowledge.............
Except, these days, anyone can go to google images, get a picture, post it up and claim that as definitive evidence to "prove" whatever point they were trying to make. Unfortunately, the number of people who have the mental accurity to actually understand and process that easily gathered information is much smaller.
To make this point i have taken your torque curves and converted them to tractive effort plots, which show torque at the wheels for each car plotted verses speed:
As you can see, there is no requirement for the diesel driver to change gear anymore than the gasoline verisons driver
Infact, the opposite is true , and the higher BMEP of the diesel more than offsets the reduction (numerically) in final drive ratio, hence the diesel actually outperforms the gasoline car at all roadspeeds (hence it manages 5.6s to 62mph, vs 5.9). Add in the Co2 advantage (135g/km vs 147g/km) and it is very simple to see why lots and lots of people buy the diesel version!
So, to repeat myself, the "diesels need to change gear all the time" is a fallacy , propogated by people who don't fully understand the relationship between tractive effort and flywheel torque. Luckily for us, the manufacturers, and the people like me who develop their cars do have this appreciation.
;-)
Oh yes, so instead of 'going to Google images' you've just made sh*t up. That graph is wrong as you don't have a clue what the gearing is, you've just guessed. I have actually driven a diesel you know (indeed lots of them) and without exception they all need lots of gear changes, just look at the feck the 330d has an 8sp box ffs, that should tell you everything you need to know by itself. Except, these days, anyone can go to google images, get a picture, post it up and claim that as definitive evidence to "prove" whatever point they were trying to make. Unfortunately, the number of people who have the mental accurity to actually understand and process that easily gathered information is much smaller.
To make this point i have taken your torque curves and converted them to tractive effort plots, which show torque at the wheels for each car plotted verses speed:
As you can see, there is no requirement for the diesel driver to change gear anymore than the gasoline verisons driver
Infact, the opposite is true , and the higher BMEP of the diesel more than offsets the reduction (numerically) in final drive ratio, hence the diesel actually outperforms the gasoline car at all roadspeeds (hence it manages 5.6s to 62mph, vs 5.9). Add in the Co2 advantage (135g/km vs 147g/km) and it is very simple to see why lots and lots of people buy the diesel version!
So, to repeat myself, the "diesels need to change gear all the time" is a fallacy , propogated by people who don't fully understand the relationship between tractive effort and flywheel torque. Luckily for us, the manufacturers, and the people like me who develop their cars do have this appreciation.
;-)
Edited by Max_Torque on Sunday 28th April 01:28
Baryonyx said:
As in, the new shape Astra? If you think that's rough you should try the mk5 Astra diesels! The new Astra diesels go some way to fixing the inherent 'diesel flaws' of the old cars. Notably...
This was a 2.0 CDTI in the newest shape, but it really was appalling. I'm used to the VAG 2.0 CR TDI and the Astra genuinely felt like stepping back a decade!- The throttle response is much improved. The mk5 throttle was like mush, and extremely lazy. The new Astra's throttle is much sharper. It wouldn't pass muster against a good petrol, but it eclipses the old effort.
- Turbo lag is considerably decreased. The mk5 was littered with flat spots. The new Astra's turbo seems much more perky, and gone are the yawning gaps in power delivery. The mk5's second gear was absolutely horrendous beneath 3000rpm on a flat surface, never mind uphill. Save for a slightly short 3rd gear in the new Astra 6 speed, it's better.
- The engine is quieter at idle. It still sounds rough, but the insistent, loud 'clackclackclacklacklack' of the mk5 is much better disguised now.
Fastdruid said:
So to repeat myself, Diesels have a tiny but massive torque spread *requiring* either an auto-box or frantic gearchanges. They don't stick 15+ speed gearboxes on trucks for sh*ts and giggles you know.
Could not put it better myself. Unless it was for tax/ co2 reasons I'd never buy a manual diesel.
I enjoyed the 530d e60 auto I had, and it was reliable in its first 100k miles before I sold it....It was a 36mpg car, compared to my Cayman S doing 29mpg on the same commute. I'm not sure if on an older car I'd risk the complexity of a diesel over a normally aspirated petrol for such a relatively modest benefit.
I like the idea of the frugal petrol trend, and I've enjoyed driving twinairs, multiairs, ecoboosts and Such recently, but I do wonder if these turbo petrols are going to rack up big bills after 100k too. After all,they have a lot of complexity compared to non turbos....
That's why I'd advise going 330i over either 328i or 330d for the long haul....
I like the idea of the frugal petrol trend, and I've enjoyed driving twinairs, multiairs, ecoboosts and Such recently, but I do wonder if these turbo petrols are going to rack up big bills after 100k too. After all,they have a lot of complexity compared to non turbos....
That's why I'd advise going 330i over either 328i or 330d for the long haul....
Fastdruid said:
Max_Torque said:
Well, what can i say, i bow to your superior knowledge.............
Except, these days, anyone can go to google images, get a picture, post it up and claim that as definitive evidence to "prove" whatever point they were trying to make. Unfortunately, the number of people who have the mental accurity to actually understand and process that easily gathered information is much smaller.
To make this point i have taken your torque curves and converted them to tractive effort plots, which show torque at the wheels for each car plotted verses speed:
As you can see, there is no requirement for the diesel driver to change gear anymore than the gasoline verisons driver
Infact, the opposite is true , and the higher BMEP of the diesel more than offsets the reduction (numerically) in final drive ratio, hence the diesel actually outperforms the gasoline car at all roadspeeds (hence it manages 5.6s to 62mph, vs 5.9). Add in the Co2 advantage (135g/km vs 147g/km) and it is very simple to see why lots and lots of people buy the diesel version!
So, to repeat myself, the "diesels need to change gear all the time" is a fallacy , propogated by people who don't fully understand the relationship between tractive effort and flywheel torque. Luckily for us, the manufacturers, and the people like me who develop their cars do have this appreciation.
;-)
Oh yes, so instead of 'going to Google images' you've just made sh*t up. That graph is wrong as you don't have a clue what the gearing is, you've just guessed. I have actually driven a diesel you know (indeed lots of them) and without exception they all need lots of gear changes, just look at the feck the 330d has an 8sp box ffs, that should tell you everything you need to know by itself. Except, these days, anyone can go to google images, get a picture, post it up and claim that as definitive evidence to "prove" whatever point they were trying to make. Unfortunately, the number of people who have the mental accurity to actually understand and process that easily gathered information is much smaller.
To make this point i have taken your torque curves and converted them to tractive effort plots, which show torque at the wheels for each car plotted verses speed:
As you can see, there is no requirement for the diesel driver to change gear anymore than the gasoline verisons driver
Infact, the opposite is true , and the higher BMEP of the diesel more than offsets the reduction (numerically) in final drive ratio, hence the diesel actually outperforms the gasoline car at all roadspeeds (hence it manages 5.6s to 62mph, vs 5.9). Add in the Co2 advantage (135g/km vs 147g/km) and it is very simple to see why lots and lots of people buy the diesel version!
So, to repeat myself, the "diesels need to change gear all the time" is a fallacy , propogated by people who don't fully understand the relationship between tractive effort and flywheel torque. Luckily for us, the manufacturers, and the people like me who develop their cars do have this appreciation.
;-)
Edited by anonymous-user on Sunday 28th April 01:28
I like your "i have actually driven a diesel you know " bit BTW!
Finally, both Gasoline and Diesel F30 3 series have 8 speed gearboxes. This is to maximise fuel economy (the huge overlap on the tractive effort curves shows they don't need them for performance reasons) by optimising the engine operating zone to coincide with the narrow high BSFC "island" resulting from the multi dimensional engine optimisiation architecture.
Edited by anonymous-user on Sunday 28th April 11:43
Fittster said:
The solution is clearly a hybrid 
I still keep lovingly looking at the ActiveHybrid 5s on the BMW AUC site, such an incredible amount of car for the money now they've suffered the initial depreciation:
It is literally the perfect BMW with the performance and soundtrack from a 535i, a nice automatic gearbox, sensible alloys/ suspension (no M Sport nonsense here) and 45mpg/ 149g/ km co2
Well if nothing else some interesting points being made. I'm actually not intending to buy either car but find it interesting to consider the sheep like way society is currently working... for example if you search for "up to 1 year old" BMW 3-Series on Autotrader you find 79 Petrol against 635 Diesel. Changing a 3 series into 5 series makes it even more significant with 5 Petrol playing 296. Some 5-10 years ago the Diesel was the exception and a little bit different, now it is clear that for most larger cars the Petrol model is the exception.
I personally think that whilst Diesels have become much quieter and more accepted by society, we have actually learned as a group to accept more gruff sounding cars in return for greater fuel economy. For me it was a interesting comparison to note how many company car drivers would plump for the 330d when in fact the 328i is barely slower (I accept it is slower but still quicker than most) and actually potentially has a significant tax advantage too. Also interesting to see the comment about the comparatively poor refinement of 6 cyl diesel S-Class et al as I'm not sure I see the benefit of this class of car without exceptional levels of refinement.
I personally think that whilst Diesels have become much quieter and more accepted by society, we have actually learned as a group to accept more gruff sounding cars in return for greater fuel economy. For me it was a interesting comparison to note how many company car drivers would plump for the 330d when in fact the 328i is barely slower (I accept it is slower but still quicker than most) and actually potentially has a significant tax advantage too. Also interesting to see the comment about the comparatively poor refinement of 6 cyl diesel S-Class et al as I'm not sure I see the benefit of this class of car without exceptional levels of refinement.
Max_Torque said:
Well, what can i say, i bow to your superior knowledge.............
Except, these days, anyone can go to google images, get a picture, post it up and claim that as definitive evidence to "prove" whatever point they were trying to make. Unfortunately, the number of people who have the mental accurity to actually understand and process that easily gathered information is much smaller.
To make this point i have taken your torque curves and converted them to tractive effort plots, which show torque at the wheels for each car plotted verses speed:
As you can see, there is no requirement for the diesel driver to change gear anymore than the gasoline verisons driver
Infact, the opposite is true , and the higher BMEP of the diesel more than offsets the reduction (numerically) in final drive ratio, hence the diesel actually outperforms the gasoline car at all roadspeeds (hence it manages 5.6s to 62mph, vs 5.9). Add in the Co2 advantage (135g/km vs 147g/km) and it is very simple to see why lots and lots of people buy the diesel version!
So, to repeat myself, the "diesels need to change gear all the time" is a fallacy , propogated by people who don't fully understand the relationship between tractive effort and flywheel torque. Luckily for us, the manufacturers, and the people like me who develop their cars do have this appreciation.
;-)
Thank you, this is very interesting. Can you please share the formula or the excel file? How are you calculating this please?Except, these days, anyone can go to google images, get a picture, post it up and claim that as definitive evidence to "prove" whatever point they were trying to make. Unfortunately, the number of people who have the mental accurity to actually understand and process that easily gathered information is much smaller.
To make this point i have taken your torque curves and converted them to tractive effort plots, which show torque at the wheels for each car plotted verses speed:
As you can see, there is no requirement for the diesel driver to change gear anymore than the gasoline verisons driver
Infact, the opposite is true , and the higher BMEP of the diesel more than offsets the reduction (numerically) in final drive ratio, hence the diesel actually outperforms the gasoline car at all roadspeeds (hence it manages 5.6s to 62mph, vs 5.9). Add in the Co2 advantage (135g/km vs 147g/km) and it is very simple to see why lots and lots of people buy the diesel version!
So, to repeat myself, the "diesels need to change gear all the time" is a fallacy , propogated by people who don't fully understand the relationship between tractive effort and flywheel torque. Luckily for us, the manufacturers, and the people like me who develop their cars do have this appreciation.
;-)
Edited by Max_Torque on Sunday 28th April 01:28
Chris Hinds said:
So let's say you walk into a BMW showroom. You want a 3-series, one that's quicker than the standard 320d. You're mulling over a 328i or 330d... both automatic since you can't have a manual 330d. By the time you add auto there's about £2700 difference with the 328i cheaper. Petrol costs you £150 more in tax over 3 years, leaving £2550 for extra fuel. Sure the 330d could well be a little faster (much of the advantage probably negated by the auto box) but the 328i weighs 185kg less over the front wheels...
Having just spent a few days in a new 530d M Sport I can honestly say that I would go with the diesel, it was very refined and smooth with bags of shove, it even sounded like a 6 cylinder petrol but much more bassy. Coupled with the 8 speed auto it was a superb drive train.If the price is right I will have no doubt in my mind to order a new 330d in a couple of years time.
kinimod1 said:
Thank you, this is very interesting. Can you please share the formula or the excel file? How are you calculating this please?
Take the (measured) plot of torque against RPM; then scale the torque axis by the gear ratio and the RPM axis by the inverse of the gear ratio for each gear and superimpose the graphs on top of each other. So if you had gear+final drive ratios of: 5:1, 4:1, 3:1, 2:1 and 1:1 a point {X,Y} on the dynograph (where X is the torque and Y is the RPM) would map to {5X,Y/5}, {4X, Y/4}, {3X,Y/3}, {2X,Y/2} and {X,Y} for each gear. Do that for the entire graph and you end up with lines like those above.
doogz said:
Fastdruid said:
Oh yes, so instead of 'going to Google images' you've just made sh*t up. That graph is wrong as you don't have a clue what the gearing is, you've just guessed. I have actually driven a diesel you know (indeed lots of them) and without exception they all need lots of gear changes, just look at the feck the 330d has an 8sp box ffs, that should tell you everything you need to know by itself.
I'm not interested in you having a pop at one of the most knowledgeable people on here, when it comes to this subject, although it is a bit silly, the man knows his s
t.I'd just like to point out that the petrol 3 series has the same 8 speed ZF box as the diesel variant. So that actually tells you approximately dick.
Fastdruid said:
Oh yes, so instead of 'going to Google images' you've just made sh*t up. That graph is wrong as you don't have a clue what the gearing is, you've just guessed. I have actually driven a diesel you know (indeed lots of them) and without exception they all need lots of gear changes, just look at the feck the 330d has an 8sp box ffs, that should tell you everything you need to know by itself.
What are you chatting? For a start that gearbox is in the petrol variants as has already been said and in many circumstances I need less gear changes in my 320d than many of the petrol cars I've owned / driven due to it having much more torque.Edited by Urban Sports on Tuesday 13th August 08:16
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