First, let me say that you should thoroughly read and reread ALL of CobaltSSOverboosters threads as well as GMTech's posts and others. Then reread again. These are advanced tables which should not be manipulated without full understanding of the LNF ecm.
Second, I don't post a lot for a reason. But, I think with all the help of the previous pioneers it is important to continue to extend the knowledge gained to others. I WILL NOT SHARE NUMBERS WITH ANYONE. THIS IS A HOW-TO, NOT A HOW MUCH THREAD. YOU WILL HAVE TO LEARN ON YOUR OWN. NO FREE HANDOUTS.
Third, ALL of my changes together will give your LNF a linear cable-driven throttle feel. They require a full retune from scratch when you make several of these changes. Why? Because many tables act as "urgency" tables. What does this mean? If I have $21 to my name and I loan you $20, when I need it back I need it back NOW because it's extremely important to me. If I have a million dollars and I load you $20, getting it back is irrelevant. This is how many of the tables function. Changing one will greatly affect others which need to be raised. The end result will be a smooth, fully functional ecm. But, it will be frustrating at times.
READ GMTECH'S WRITEUP ON OPTIMUM SPARK TABLES FIRST. His description is spot on. It took me experimenting to understand what he had written. This is merely to explain HOW to manipulate the optimum spark table.
Some important points
- The optimum spark table is an urgency table for the ecm and is directly related to the main spark.
- The values in the optimum spark table are completely irrelevant.
- The optimum spark table is a DIFFERENCE table. The numbers that matter are the values in the optimum spark table MINUS the values in the main spark.
- Changes to the optimum spark table can make it try to boost way to quickly out of control OR not boost at all up to redline.
HOW TO ADJUST THE OPTIMUM SPARK TABLE
Like I said above, it is a difference table. I will first list how to make changes to the optimum spark and the main spark. Then, I will explain what's happening.
To adjust the optimum spark table:
1. Like your main spark, all four OS tables should be the same. Very important.
2. Highlight and copy an entire main spark table
3. Highlight an entire OS table.
4. Right click -> paste special -> SUBTRACT. You are subtracting the MS table from the OS table. The values you are left with (the difference) is what you will adjust.
5. Adjust your OS table.
6. Highlight that adjusted OS table.
7. Right click -> paste special -> ADD. You are adding back in the values of the MS table that you subtracted.
8. Don't forget to copy that new OS table to the other three old ones.
Step #7 is very important. If you forget to add it back in, the car will run like it's in limp mode for a reason that will be explained below. Ask me how I know
To adjust your main spark table without affecting your optimum spark values:
1. Highlight and copy an entire main spark table.
2. Highlight an entire optimum spark table.
3. Right click -> paste special -> SUBTRACT. You are subtracting the old MS table from your OS table leaving you with your OS values that you DON'T want to change.
4. Make the changes you want to your main spark table.
5. Copy that main spark table to the other three old MS tables.
6. Go back to the OS table that you subtracted from and right click -> paste special -> ADD. You are adding your new MS values to the old OS values you didn't want to change.
7. Copy the "new" OS table (same OS values with the new MS changes added to it) to the other three "old" OS tables.
This will let you make timing changes without changing the optimum spark. Remember, it's an urgency table. Just because you want different timing values doesn't mean you want to change the urgency with which they are applied.
WHAT THE OPTIMUM SPARK TABLE IS DOING
Like Mike said below (thanks), this is one of the more dominant urgency tables. When talking about what it does, I will be referring to the DIFFERENCE with the main spark table subtracted. Like the money example above, negative numbers mean little urgency while positive numbers mean you are more desperate for results.
Start with the stock table. With the stock timing subtracted, notice how the numbers in the low load, high rpm area are negative? Also notice how in the high load region they approach 23+? What this does is tell the ecm that making torque (everything involved from timing to boost, etc) in low load high rpm areas is unimportant. Conversely, it's saying there is much more urgency in the higher rpm and load regions.
When you have been changing timing without adjusting the optimum spark along with those spark changes as noted above, you were unknowingly also changing the urgency with which you were requesting power. That's why you can make several main spark changes and think "wow the engine really woke up!" or "man the engine went flat just with a timing change. What gives?" It wasn't always the timing as much as it was the difference between main spark and optimum spark.
As a safe method of seeing what power the optimum spark table has, set the difference (as explained above) to "-10" across the whole table. I like using "-10" as a more dramatic example. Add your main spark table back in and go make a pull through the gears. Then, repeat with making the entire difference "5" or "10" like Mike said and make another run. This will give you an understanding of HOW to manipulate the optimum spark and what it does to overall performance with a single table. "50" seems to be the max for instability on a stock turbo. Stay well below this.
One final note on linear pedal. Why set the entire difference to a single value? It makes the table's response linear. It sees a constant "urgency" request. I've tried ramping it and it makes the pedal exponential. Making the table a single value doesn't change the urgency of the pedal regardless at what percentage you are. The ecm responds by ramping torque in linearly. This combines with other tables mentioned to create a cable-driven pedal feel.