I am getting back into tuning on my '11 STI. All of my previous experience comes from tuning 16bit WRXs so my STI is a significant step up in complexity. I am starting with DBW tuning just so that I can get a grip on how it works and be a prelude to boost control and AVCS. What I am looking for is feedback on the approach I am taking with DBW tables. See below.
I've spent a few hours combing through the forums and absorbing the info. From what I can tell, there really isn't much info on how to effectively tune DBW on CAN based STIs that come with 3 major tables (instead of 2 on previous years):
- Requested Torque
- Requested Torque Base
- Target Throttle Plate Position
The new complexity is the base table that is used as a divider to calculate a ratio which is than used in the target table to establish the target throttle opening, formula:
requested torque / torque base value = target throttle ratio
My initial reaction is that it is difficult to get a grip on how the changes in each table will affect the behavior of the car. So, I started to ponder if there is a way make this a bit easier and I came up an approach but I'd like to hear people's feedback on this.
1. Stock requested torque table makes little sense to me, in practical terms, since the settings change with RPM. As a driver, I know what I want at any given time so I'd rather see the table work as a constant value for a given throttle input for all RPMs. Below is a first stab at this (sport # mode) where I scaled the table in linear fashion: 25% throttle means 25% requested torque, 50% throttle means 50% requested torque, etc etc. Note the max value of 450.
2. Now, what about this divider base value? The approach that I took is to set the entire table to my max value in requested torque table (450). What that does effectively is that every value in the requested torque table will be divided by the max thus making the calculated ratio become the percentage of the requested torque, for any RPM. For example, 300 / 450 becomes 0.67 which is 67% of the max value. At least for me, this gives me an easy mental picture on what the ratio values mean in the next table.
3. Lastly, I rescaled the target throttle table in a linear fashion, similar to what I did in requested torque table. Since the ratio is now the percentage of requested torque, it's easy to anticipate what the values will lead to when the ECU dials in the throttle position. Again, this is a first shot and I don't know what these settings will 'feel' like when I drive the car. But, this helps me in wrapping my mind around this triple table concoction.
What are your thoughts on this? Please post your feedback and let me know if this makes sense. I will try this on the car and see what the settings feel like. I will likely end up making adjustments in requested torque table as this will play nicely into the boost control system adjustments. For example, I am end up upping some RT values which will yield a higher ratio and end up with higher throttle target in relation to the actual throttle input. We'll see how this goes.