The base timing is for starting and limp home mode. The way the ECM handles timing is it reads from a table with several variables. It adds the timing in this table. If the base is set at 4* and the table says 22* then the total timing is 26*. I had my son's '90 454SS set at 8*. You can set the base wherever you want as long as it will run without the ECM hooked up and still start. One other thing is that you add too much timing you will get pinging. You may not notice the pinging because the knock sensor will hear it first and back off the timing, and therefore your performance will decrease.
The ideal way to get as much timing as you can without pinging, is to data log and watch the knock counts. There are a couple free data loggers on the net and plans to build a cable to hook up your laptop to the ALDL port. You can drive and data log, then change the timing and then drive and data log until you get it where you want it.
1
