Question about map scales and VTEC crossover cam angles
Posted: Mon Sep 17, 2012 1:30 am
I recently had the PRA ECU in my Lotus Elise with a EUDM K20A2 (and some goodies) upgraded with a K-pro3 and have been looking into the specifics of the K-pro wrt. setting it up and remapping it.
I do have some experience with using generic mappable ECU's on various engines and in most areas the K-pro looks and feels quite familiar. Have to get used a little to the fact that it doesn't do 'live' changes like most aftermarket ECU's so it requires a little different approach on the dyno.
There are, however, two things I'm curious about which relate to the low-speed and high-speed maps. Not so much a technical issue, but more a question of the reasoning why things are commonly done in these calibrations..
My first question is about the rpm range map scaling for both the low-speed and high-speed maps.
I have read the various docs on map scaling, tech and training info and examined various example/base calibrations.. I noticed that it seems common to rescale the high speed cam tables to start at a higher rpm as it would never use the low entries anyway because the VTEC crossover rpm's are higher so by dropping the low rpm entries you get extra cells available. That's clear to me..
However, I'm curious why the low-speed cam tables usually run up to 8100rpm or more, even if the VTEC switchover points are for instance set between 4000 and 6000 rpm.
Would it not make sense to re-scale the low-speed cam tables to 0-6500rpm as it should not be using anything over 6000rpm in this map anyway?
Or is there some (implicit) reason for the low-speed cam table to be extended all the way to 8000+rpm? (eg. fail-safe for an oil pressure drop forcing VTEC to drop from the high-speed to the low-speed cam?)
To get the highest cell-resolution in the tables I would personally scale them back to the rpm ranges that the engine is set up for, but perhaps I'm missing some blindingly obvious point here. Just curious :)
The second question is about the optional cam angle adjustments between the low-speed and high-speed maps by pre-rotating the cams towards the high-speed setting to make the transition as smooth as possible.
The tech-docs and training files only seem to perform this action for the high-load (full throttle) crossover point.
I assume (perhaps incorrectly) that when a low and high rpm crossover point is set that the ECU interpolates the MAP/load values from each to get an imaginary range/line between the 2 extremes where the switchover will happen between these points.
So you could, in theory, set up cam angle pre-adjustment values on the whole VTEC switchover rpm-load range in the low-speed map where required instead of only the full throttle part (last columns). But this doesn't seem to be commonly done, so I'm curious about the reason..
I suspect that the effect of the cam change delay on a large 'step' is less and less on smaller throttle openings, so this adjustment would in the end be more of a fine-tuning/tweaking step and not have that much impact (apart from perhaps making it more smooth..). Correct? Barking up the wrong tree?
Any background info is much appreciated.
Bye, Arno.
I do have some experience with using generic mappable ECU's on various engines and in most areas the K-pro looks and feels quite familiar. Have to get used a little to the fact that it doesn't do 'live' changes like most aftermarket ECU's so it requires a little different approach on the dyno.
There are, however, two things I'm curious about which relate to the low-speed and high-speed maps. Not so much a technical issue, but more a question of the reasoning why things are commonly done in these calibrations..
My first question is about the rpm range map scaling for both the low-speed and high-speed maps.
I have read the various docs on map scaling, tech and training info and examined various example/base calibrations.. I noticed that it seems common to rescale the high speed cam tables to start at a higher rpm as it would never use the low entries anyway because the VTEC crossover rpm's are higher so by dropping the low rpm entries you get extra cells available. That's clear to me..
However, I'm curious why the low-speed cam tables usually run up to 8100rpm or more, even if the VTEC switchover points are for instance set between 4000 and 6000 rpm.
Would it not make sense to re-scale the low-speed cam tables to 0-6500rpm as it should not be using anything over 6000rpm in this map anyway?
Or is there some (implicit) reason for the low-speed cam table to be extended all the way to 8000+rpm? (eg. fail-safe for an oil pressure drop forcing VTEC to drop from the high-speed to the low-speed cam?)
To get the highest cell-resolution in the tables I would personally scale them back to the rpm ranges that the engine is set up for, but perhaps I'm missing some blindingly obvious point here. Just curious :)
The second question is about the optional cam angle adjustments between the low-speed and high-speed maps by pre-rotating the cams towards the high-speed setting to make the transition as smooth as possible.
The tech-docs and training files only seem to perform this action for the high-load (full throttle) crossover point.
I assume (perhaps incorrectly) that when a low and high rpm crossover point is set that the ECU interpolates the MAP/load values from each to get an imaginary range/line between the 2 extremes where the switchover will happen between these points.
So you could, in theory, set up cam angle pre-adjustment values on the whole VTEC switchover rpm-load range in the low-speed map where required instead of only the full throttle part (last columns). But this doesn't seem to be commonly done, so I'm curious about the reason..
I suspect that the effect of the cam change delay on a large 'step' is less and less on smaller throttle openings, so this adjustment would in the end be more of a fine-tuning/tweaking step and not have that much impact (apart from perhaps making it more smooth..). Correct? Barking up the wrong tree?
Any background info is much appreciated.
Bye, Arno.