16-08-2012, 01:40 AM
I'm in the process of doing some testing in this area but it's very tough.
For instance, on the HDi90 you can inject earlier to get better efficiency, but to finish injecting sooner you probably need to run more rail pressure, otherwise you might start injecting way too early and start to get issues with fuel atomisation becoming not optimal.
So you up rail pressure but now the rail pump runs a slight bit harder and that might cost you all the extra torque you found by changing the injection timing.
There really are so many variables to consider that it is hard to balance things. Even the worlds best engineers who do this work day in day out for OEM's will see odd results and tune things in weird ways to get certain results that go against logic.
So it is hard to go, X results in Y, so Z change will achieve my goal. They are general rules but since every engine has it's own idiosyncrasies due to all manner of mechanical properties it is as said just really hard to do.
I often say that although OEM's build to a compromise, the fact they have SO much skill/money to find that compromise that it's often a better solution than an 'un-compromised' solution provided by someone with much less skill and support and applying the correct knowledge but without fine consideration for the exact implementation of their product.
You do often see tuners say that they get more power because of fuel issues in some countries, or needing to operate ok in 50degC conditions, or miss a service etc etc... but in my view it's all just lies.
They push engines and they will ultimately cause MORE stress and strain in the longer run than the OEM.
A HDi has a temp sensor, so for instance it doesn't matter if you drive your remapped car to the north pole, the car will adjust it's fuelling appropriately to the conditions. Skip a service, then the coolant is worse, so heats up faster? Engine temp sensor sees it and trims to keep things safe.
Oil old, turbo lazy, MAF readings stay lower longer, trimming fuelling and controlling smoke.
Worst case EML comes on and we get 'safe' limp mode.
I think there are things we can improve on, but I think ANY tuner generally won't have the skill to get significantly better economy than OEM even though they have no limits on emissions, simply because they are less good with less good gear/knowledge/time etc.
If they ARE that good, they will work at BMW making F1 engine tunings, or calibrate OEM car engines, that is why the OEM's are hard to beat despite their compromises
In my XUD9, which was at the time pretty new and low mileage, I did a big long motorway commute at 70-80mph with some hooning at each end, but even then I only averaged 41mpg or so.
My HDi managed about 43-44mpg doing the same, so I do think the HDi is as or more economical than the XUD9.
It'd be an interesting test to do a brim fill on a 306 HDi/TDi and then go for a 100 mile cruise on the same day/patch of road/traffic, then pull off and re-brim and see what mpg they really are getting vs each other in cruise only conditions!
Hmmmm
Dave
For instance, on the HDi90 you can inject earlier to get better efficiency, but to finish injecting sooner you probably need to run more rail pressure, otherwise you might start injecting way too early and start to get issues with fuel atomisation becoming not optimal.
So you up rail pressure but now the rail pump runs a slight bit harder and that might cost you all the extra torque you found by changing the injection timing.
There really are so many variables to consider that it is hard to balance things. Even the worlds best engineers who do this work day in day out for OEM's will see odd results and tune things in weird ways to get certain results that go against logic.
So it is hard to go, X results in Y, so Z change will achieve my goal. They are general rules but since every engine has it's own idiosyncrasies due to all manner of mechanical properties it is as said just really hard to do.
I often say that although OEM's build to a compromise, the fact they have SO much skill/money to find that compromise that it's often a better solution than an 'un-compromised' solution provided by someone with much less skill and support and applying the correct knowledge but without fine consideration for the exact implementation of their product.
You do often see tuners say that they get more power because of fuel issues in some countries, or needing to operate ok in 50degC conditions, or miss a service etc etc... but in my view it's all just lies.
They push engines and they will ultimately cause MORE stress and strain in the longer run than the OEM.
A HDi has a temp sensor, so for instance it doesn't matter if you drive your remapped car to the north pole, the car will adjust it's fuelling appropriately to the conditions. Skip a service, then the coolant is worse, so heats up faster? Engine temp sensor sees it and trims to keep things safe.
Oil old, turbo lazy, MAF readings stay lower longer, trimming fuelling and controlling smoke.
Worst case EML comes on and we get 'safe' limp mode.
I think there are things we can improve on, but I think ANY tuner generally won't have the skill to get significantly better economy than OEM even though they have no limits on emissions, simply because they are less good with less good gear/knowledge/time etc.
If they ARE that good, they will work at BMW making F1 engine tunings, or calibrate OEM car engines, that is why the OEM's are hard to beat despite their compromises
In my XUD9, which was at the time pretty new and low mileage, I did a big long motorway commute at 70-80mph with some hooning at each end, but even then I only averaged 41mpg or so.
My HDi managed about 43-44mpg doing the same, so I do think the HDi is as or more economical than the XUD9.
It'd be an interesting test to do a brim fill on a 306 HDi/TDi and then go for a 100 mile cruise on the same day/patch of road/traffic, then pull off and re-brim and see what mpg they really are getting vs each other in cruise only conditions!
Hmmmm
Dave