Ryan
February 25th, 2008, 02:32 PM
My first post here; I hope it's a good one. I have come upon a wall and no searching has uncovered anything else, so hopefully it is not just ancient information I have failed to dig up. :)
A little background:
I came across one of RedHardSupra's posts on here in regards to the lack of attribution of charge temperature in SD tuning in addition to some of his posts about temperature modeling.
Looking at the EFILive documentation for the Main VE tables (and RHS's Speed Density document), the GMVE dimensions are [ m * T / P ], resulting in an airmass when the sensor inputs are applied to their appropriate values.
With some manipulation, we can get:
Temperature = GMVE * Pressure / airmass
I also had the thought that, using a wideband, we can also (roughly) calculate the airflow (or airmass, accordingly) using the calculated injector flow rates and wideband output.
Alternatively, since I have been unable to drive around and get some calculated injector flow rates, I have assumed that the flow rates will stay roughly constant across the RPM range.
So with some conversion between the air/fuel masses and rate conversions, I have come up with:
GMVE = (120 * AFR * IFR * Temperature) / (RPM * MAP * cyl)
and
Temperature = (GMVE * RPM * MAP * cyl) / (120 * AFR * IFR)
Now, assuming that the target AFR before any modifiers is 14.63 (a major assumption, but I don't think it significantly changes the results), I used the data I have from the stock calibrations to come up with an array of what would be (or what I thought would be) "Temperature" from the GMVE and IFR across the MAP/RPM axes.
I made a quick spreadsheet in Excel to mash all of the numbers together and return some kind of plot of the value for temperature from MAP/RPM, and got a strange looking (exponential) curve (see attached Excel spreadsheet).
My questions: are there any other values that go into the calculation for the GMVE dimension (unitless values or some function)? The surface I have plotted for stock values seem to indicate some kind of natural exponential curve. Also, what does these numbers represent? They don't appear to be temperature values as they are unreasonably high ( > 2000 K).
I've attached the spreadsheet I used as well as an image of the resulting plot (for anyone that can't use Excel but is interested). I don't think I have made any kind of algebraic or formula-related mistakes, and seeing as how the values which I have assumed (i.e. constant stoich AFR) would vary linearly or approximately linearly where as the plot is obviously nonlinear, I don't think I have made any unreasonable assumptions. Please forgive the sloppy methods of referencing RPM and MAP, I am definitely no Excel god, and didn't intend on anyone else seeing the spreadsheet. :) Sorry for the novel!
A little background:
I came across one of RedHardSupra's posts on here in regards to the lack of attribution of charge temperature in SD tuning in addition to some of his posts about temperature modeling.
Looking at the EFILive documentation for the Main VE tables (and RHS's Speed Density document), the GMVE dimensions are [ m * T / P ], resulting in an airmass when the sensor inputs are applied to their appropriate values.
With some manipulation, we can get:
Temperature = GMVE * Pressure / airmass
I also had the thought that, using a wideband, we can also (roughly) calculate the airflow (or airmass, accordingly) using the calculated injector flow rates and wideband output.
Alternatively, since I have been unable to drive around and get some calculated injector flow rates, I have assumed that the flow rates will stay roughly constant across the RPM range.
So with some conversion between the air/fuel masses and rate conversions, I have come up with:
GMVE = (120 * AFR * IFR * Temperature) / (RPM * MAP * cyl)
and
Temperature = (GMVE * RPM * MAP * cyl) / (120 * AFR * IFR)
Now, assuming that the target AFR before any modifiers is 14.63 (a major assumption, but I don't think it significantly changes the results), I used the data I have from the stock calibrations to come up with an array of what would be (or what I thought would be) "Temperature" from the GMVE and IFR across the MAP/RPM axes.
I made a quick spreadsheet in Excel to mash all of the numbers together and return some kind of plot of the value for temperature from MAP/RPM, and got a strange looking (exponential) curve (see attached Excel spreadsheet).
My questions: are there any other values that go into the calculation for the GMVE dimension (unitless values or some function)? The surface I have plotted for stock values seem to indicate some kind of natural exponential curve. Also, what does these numbers represent? They don't appear to be temperature values as they are unreasonably high ( > 2000 K).
I've attached the spreadsheet I used as well as an image of the resulting plot (for anyone that can't use Excel but is interested). I don't think I have made any kind of algebraic or formula-related mistakes, and seeing as how the values which I have assumed (i.e. constant stoich AFR) would vary linearly or approximately linearly where as the plot is obviously nonlinear, I don't think I have made any unreasonable assumptions. Please forgive the sloppy methods of referencing RPM and MAP, I am definitely no Excel god, and didn't intend on anyone else seeing the spreadsheet. :) Sorry for the novel!