newmercman:
[zb] I can assure that if I was going to have an alter ego it would not be that of a Gritter Driver from Leatherhead
Now Carryfast, you really are making it difficult for yourself here, you argue with [zb]'s theory, but you don’t appear to realise what it is
So again, in plain English, here it is. He suggests changing up at max revs into the highest gear possible, so in effect it would be going all the way to 2200rpm and then changing two full gears which would drop the rpms back down to around the start of the torque curve’s plateau, then pulling hard through that until max rpms, so if you did that you would, in the case of the engine in the SFC graph, be hovering around the SFC figure of 200 all the time, but without losing so much momentum by shifting so many gears
In theory, this works, but he (and the rest of us apart from you) are wondering if it does indeed work in the real world, because maybe, just maybe, we could all learn something from this
So KR79 has kindly offered to be a lab rat for us
It’s been tried loads of times in the real world usually with the result of the guvnor moaning about the fuel costs of lead footed drivers who can’t be bothered to use a gearbox properly and before that when those drivers didn’t have a lot of choice because all they had available at peak power was (a lot) less power than a modern wagon has at peak torque and to add insult to injury a DB 6 speed box.
Those tests you have just done backs up what NMM and I have been saying, horses for courses ,urban work an auto should win out. Motorway,s or in NMM case freeways it shouldn’t make much difference.
8.79 on urban work is very commendable, I know people who can’t get that going downhill with a sail up! Personal use of an I-Shift my average was 8.25 on urban ,but without too much concentration on motorway work I could get between 9.5 and 10 for the work we were doing, which usually involved running about half way home empty and then loaded (44t) back into base.
I think if you are dealing with London traffic and giving yourself parameters like that to work in, you must either be very enthusiastic or like me , verging on being an anorak!
Carryfast:
Even if it’s distance work the basic rule of fuel efficiency for diesels is that the narrower band,either side of peak torque,that you can keep it to the more fuel efficient it will be and having plenty of manually operated close ratio gears is the best way of acheiving that ideal which has been the accepted ideal for truck design at least since the 1970’s.The only difference with something like a 730 Scania is that the fuel consumption penalties get a lot more severe the further from that ideal that they’re operated.The ability to use just half the gears available from a 12 speed box is just a result of the extremely flat torque curves (more like plateaus) that they seem to getting from modern engines.
But even in that case it would probably still help if the thing is kept as close as possible to either side of the centre of that plateau than letting it either lug down a lot lower or go far over that centre point and that ideal applies even more in the case of accelerating a fully freighted truck up an incline from low speed or standstill.Which is why if it was me ordering it I’d want that 18 speed fuller in it not an automated manual.
However the benefits of having something like the torque of a 600-700 + available is that it can maintain higher road speeds for the equivalent amount of engine speed.But driving the ‘nuts out of it’ is exactly what ZB’s theory is all about and it would be interesting to see what the fuel figures of that type of engine would be driven on the basis of foot to the floor up to peak power between each upshift.
You are missing the point
Fuel use is dictated by the SFC curve, not the torque curve (plateau)
So it doesn’t necessarily mean that a few hundred RPMs either side of the peak torque figure will be the most efficient
The method that you describe would be the way to do it if the torque was very ‘peaky’ but as today’s torque curves are more of a plateau than a curve, so short shifting either side of a specific RPM number is not necessary and could actually harm fuel consumption and journey times
kr79:
I think it depends if you are going on a long motorway trip accelerating hard up the slip road up to say 55mph on a 300 mile journey then cruising on the limiter that bit more fuel is negligible over the journey but on a varied route like I did its more noticeable.
It’s a case of knowing when to use the power you have avalible and what gear to use. You give someone a 700bhp manual lorry and they drive it sensibly they will give you half decent fuel consumption but give some one it and they drive the nuts out if it they will give you fuel figures that will hurt your wallet.
As I said yesterday using economy mode and leaving it to its own devices it changed up at just over 1500 rpm down to about 1050rpm it went 3 5 7 9 11 12. And was in the green at all times. Now IMO I shift is the best automated box avalible the changes are lightning fast as its a constant mesh box and if it was a manual 12 speed Volvo I think I’d use more gears as I think you would lose more momentum as you couldn’t change gear fast enough.
I said yesterday I generally I change up at the top of the green depending on road conditions etc. At the end of the day I’ve never looked at driving as a science just what I think is right at the time.
Thanks for making th effort, kr79. What did the I-shift do in Performance mode-did it accelerate in two-gear steps? According to the Volvo spec sheet (I assume the ratio spread is the same or similar for the Euro and US versions), a change up at 1900 would drop it back to about 1150, two gears up. I would like to see what happens if, using manual, you use a sequence 3,6,9,12, changing up at 2000-2100. This should give you about 1000rpm in the next gear. If you accelerate with full throttle, are the I-shift changes jerky?
Yeah in auto power mode changes up the lower gears two at a time at about 1900 down to 1100 and the top 3 in single steps so 1900 down to 1500.
Looking on the display it will allow you to change up a maximum of three gears il try this tommorrow and see how it performs.
Carryfast:
However the benefits of having something like the torque of a 600-700 + available is that it can maintain higher road speeds for the equivalent amount of engine speed.But driving the ‘nuts out of it’ is exactly what ZB’s theory is all about and it would be interesting to see what the fuel figures of that type of engine would be driven on the basis of foot to the floor up to peak power between each upshift.
I have 850 hp and I drive it flat to the floor, from 1200 to 2100 rpm, like every good driver does, and I get 8.3 mpg. 16 years old truck, base engine from -69, manual gears (12+2).
Like I said earlier, it has been proved many times, on the dyno and on the road, so it works, before, now and in the future.
Carryfast:
Even if it’s distance work the basic rule of fuel efficiency for diesels is that the narrower band,either side of peak torque,that you can keep it to the more fuel efficient it will be and having plenty of manually operated close ratio gears is the best way of acheiving that ideal which has been the accepted ideal for truck design at least since the 1970’s.The only difference with something like a 730 Scania is that the fuel consumption penalties get a lot more severe the further from that ideal that they’re operated.The ability to use just half the gears available from a 12 speed box is just a result of the extremely flat torque curves (more like plateaus) that they seem to getting from modern engines.
But even in that case it would probably still help if the thing is kept as close as possible to either side of the centre of that plateau than letting it either lug down a lot lower or go far over that centre point and that ideal applies even more in the case of accelerating a fully freighted truck up an incline from low speed or standstill.Which is why if it was me ordering it I’d want that 18 speed fuller in it not an automated manual.
However the benefits of having something like the torque of a 600-700 + available is that it can maintain higher road speeds for the equivalent amount of engine speed.But driving the ‘nuts out of it’ is exactly what ZB’s theory is all about and it would be interesting to see what the fuel figures of that type of engine would be driven on the basis of foot to the floor up to peak power between each upshift.
You are missing the point
Fuel use is dictated by the SFC curve, not the torque curve (plateau)
So it doesn’t necessarily mean that a few hundred RPMs either side of the peak torque figure will be the most efficient
The method that you describe would be the way to do it if the torque was very ‘peaky’ but as today’s torque curves are more of a plateau than a curve, so short shifting either side of a specific RPM number is not necessary and could actually harm fuel consumption and journey times
If I’ve read it right ZB’s theory is based on some SFC figures,rather than the old rules which as far as I know still apply,relating to use the torque not the power and keep it as close as possible to either side of the torque peak (in modern day engines obviously the centre of the plateau) regardless of how flat the torque curve is.That being most efficient method and certainly more efficient than running it up to peak power in every gear .
But if ZB’s way is the most efficient way then obviously all automated manuals would be 6 speed max just using upshift points which reflect an engine operating range which spans from around 1,000 rpm up to peak power with no need for manual override except for slow speed manouvreing.
Which seems to be the ultimate steering wheel attendant wagon just floor the accelerator in most situations and brake when required.
for a while (almost ayear )had to drive a 81 scannie no turbo and 5 gear,and suince that always been wondering why spec a non motor whitout gears, that as the Volvo 614 six gears should have needed the double,or a18 speed fuller ,whit more power as a85 scannie whit turbo and 5gears the only problem was a to high geared reverse,cheers benkku
Well no it has 12 gears to cover different scenarios that occur on different roads at different weights in real life not on graph or a computer screen. But imho 12 gears is enough for a modern truck at standard weights to have to cover all eventualitys wether they be in a manual or automated gearbox.
Carryfast:
If I’ve read it right ZB’s theory is based on some SFC figures,rather than the old rules which as far as I know still apply,relating to use the torque not the power and keep it as close as possible to either side of the torque peak (in modern day engines obviously the centre of the plateau) regardless of how flat the torque curve is.That being most efficient method and certainly more efficient than running it up to peak power in every gear .
But if ZB’s way is the most efficient way then obviously all automated manuals would be 6 speed max just using upshift points which reflect an engine operating range which spans from around 1,000 rpm up to peak power with no need for manual override except for slow speed manouvreing.
Which seems to be the ultimate steering wheel attendant wagon just floor the accelerator in most situations and brake when required.
The “rules” use the SFC of the engine as their basis, along with concerns about durability, I would guess. They may have been simplified for the sake of steering wheel attendants, who may need to told not to sit at high rpm, when driving at a steady speed. Just don’t take them at face value. Investigate. That is what we are doing here, I believe, and jolly fun it is too.
kr79:
Well no it has 12 gears to cover different scenarios that occur on different roads at different weights in real life not on graph or a computer screen. But imho 12 gears is enough for a modern truck at standard weights to have to cover all eventualitys wether they be in a manual or automated gearbox.
Coincidently I thought that the old constant mesh ZF 12 speed splitter was one of the best boxes I ever used.In most cases 10 were enough which just meant four gearshifts using the stick and use the splitter for the rest.As I’ve said elswhere that together with the old turbocharged Merc V8 would have been ideal at least up to 40 t gross.
After reading these confusing comments can someone tell me where im going wrong, i drive a CF Daf 460 double drive and the green band is between 1100rpm and 1500 rpm ,i normally set off in 2nd low ,then 4th low then 5th low ,once in top box i keep the revs between 1400rpm and 1200rpm with half gear up shifts and 1500rpm and 1100 rpm on full gear up shifts depending on the road and traffic conditions .I have the fuel consumption information on all the time , today i let it lug at 1100rpm where it struggled but kept pulling ,then i dropped half a gear and the revs went up to around 1350 rpm ,the fuel consumption also went up from 95 litres /100kms to 150 litres /100kms .The double drives are poor on fuel im averaging around 5.5mpg but we run at top weight on hilly terrain and the CF is low geared
ramone:
After reading these confusing comments can someone tell me where im going wrong, i drive a CF Daf 460 double drive and the green band is between 1100rpm and 1500 rpm ,i normally set off in 2nd low ,then 4th low then 5th low ,once in top box i keep the revs between 1400rpm and 1200rpm with half gear up shifts and 1500rpm and 1100 rpm on full gear up shifts depending on the road and traffic conditions .I have the fuel consumption information on all the time , today i let it lug at 1100rpm where it struggled but kept pulling ,then i dropped half a gear and the revs went up to around 1350 rpm ,the fuel consumption also went up from 95 litres /100kms to 150 litres /100kms .The double drives are poor on fuel im averaging around 5.5mpg but we run at top weight on hilly terrain and the CF is low geared
nothing wrong,it dipend on the driving condissions, carryfast and the boys are talking of HIGHWAYdriving ,cheers benkku
ramone:
After reading these confusing comments can someone tell me where im going wrong, i drive a CF Daf 460 double drive and the green band is between 1100rpm and 1500 rpm ,i normally set off in 2nd low ,then 4th low then 5th low ,once in top box i keep the revs between 1400rpm and 1200rpm with half gear up shifts and 1500rpm and 1100 rpm on full gear up shifts depending on the road and traffic conditions .I have the fuel consumption information on all the time , today i let it lug at 1100rpm where it struggled but kept pulling ,then i dropped half a gear and the revs went up to around 1350 rpm ,the fuel consumption also went up from 95 litres /100kms to 150 litres /100kms .The double drives are poor on fuel im averaging around 5.5mpg but we run at top weight on hilly terrain and the CF is low geared
Make only full gear upshifts in high range if you are not climbing. And forget the temporary fuel consumption gauge, it’s irrelevant information.
ramone:
After reading these confusing comments can someone tell me where im going wrong, i drive a CF Daf 460 double drive and the green band is between 1100rpm and 1500 rpm ,i normally set off in 2nd low ,then 4th low then 5th low ,once in top box i keep the revs between 1400rpm and 1200rpm with half gear up shifts and 1500rpm and 1100 rpm on full gear up shifts depending on the road and traffic conditions .I have the fuel consumption information on all the time , today i let it lug at 1100rpm where it struggled but kept pulling ,then i dropped half a gear and the revs went up to around 1350 rpm ,the fuel consumption also went up from 95 litres /100kms to 150 litres /100kms .The double drives are poor on fuel im averaging around 5.5mpg but we run at top weight on hilly terrain and the CF is low geared
That’s about right mate for one of them best motor I ever had on landfill work was a scania 124 420 used to average about 6mpg. Had a foden 4525 struggled to hit 5mpg.
Double drive will drop around 1mpg compared to a 6x2 before you take into account you will probaly be dragging a low loader or bulk rubbish trailer behind you. Then take in to account you are probaly going places where economical driving comes second to actualy keeping moving then pto use etc.
Carryfast:
If I’ve read it right ZB’s theory is based on some SFC figures,rather than the old rules which as far as I know still apply,relating to use the torque not the power and keep it as close as possible to either side of the torque peak (in modern day engines obviously the centre of the plateau) regardless of how flat the torque curve is.That being most efficient method and certainly more efficient than running it up to peak power in every gear .
Sorry, old rules don’t apply, never have.
You don’t even seem to understand what are torque and power. There is no torque without power or power without torque. You never even get full torque at lower gears when driving your way because turbo never has enough time to reach maximum boost.
ramone:
After reading these confusing comments can someone tell me where im going wrong, i drive a CF Daf 460 double drive and the green band is between 1100rpm and 1500 rpm ,i normally set off in 2nd low ,then 4th low then 5th low ,once in top box i keep the revs between 1400rpm and 1200rpm with half gear up shifts and 1500rpm and 1100 rpm on full gear up shifts depending on the road and traffic conditions .I have the fuel consumption information on all the time , today i let it lug at 1100rpm where it struggled but kept pulling ,then i dropped half a gear and the revs went up to around 1350 rpm ,the fuel consumption also went up from 95 litres /100kms to 150 litres /100kms .The double drives are poor on fuel im averaging around 5.5mpg but we run at top weight on hilly terrain and the CF is low geared
That’s about right mate for one of them best motor I ever had on landfill work was a scania 124 420 used to average about 6mpg. Had a foden 4525 struggled to hit 5mpg.
Double drive will drop around 1mpg compared to a 6x2 before you take into account you will probaly be dragging a low loader or bulk rubbish trailer behind you. Then take in to account you are probaly going places where economical driving comes second to actualy keeping moving then pto use etc.
Im trying to understand reving engines up to 2000 rpm then change up 2 gears ,i would think it would do more harm than good im not a fan of screwing engines
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