When I first switch to electronic timing control, I made the mistake of listening to everyone. Put the cruise timing up to 40 and it will help fuel economy. Big mistake. After driving like this for a couple summers I started to notice a loss in oil pressure. So I pulled the 383 and was going to freshen it up until I got the dreaded call from the engine builder. It had pounded out the tops of the rod bearings and the bottom of the main. It was building to much cylinder pressure at TDC because the timing was over advanced. It was trying to push the crank out the bottom of the engine. So I ended up buying a new rotating assembly.
After the rebuild, I decided to do a little testing. I setup the knock sensors, created a couple advanced tables and found a nice long stretch of flat hi-way. I set the timing to what would be considered a normal SBC timing curve. 18 initial, 36 total, all in by 3000rpm. I set the target AFR at 14.7 in the cruise area and went for a drive. It ran well, and the plugs looked good. Then I used one of the Advanced tables to off set the AFR by 1.3, which would take the Target AFR to 16:1. I used an input to turn this table on and off when I wanted. Once out on the nice flat hi-way I got it to a steady speed and then I could flip the switch to see what happened. I logged what it was doing. With just leaning it out I could feel the lose of power. And the log backed me up. I could see the drop in RPM and MPH. So for the second test I set the target AFR to 16:1 and set the switch to control timing. I set the Advanced table to add 5 degrees of timing when I flip the switch. Went out to my test area and got it up to a steady speed. This time when I flipped the switch, I could feel the increase in power, and the logs verified this. So I set up the new timing table with 5 more degrees of timing in this area and went out again. This time when I flipped in another 5 degrees of timing and I felt no difference. And the logs showed no change in MPH, RPM of fuel economy. So I changed the Advanced timing table to add 10 degrees of timing. Again the same results, no change. Right now I run at 1900rpm at 65mph with 28 degrees of timing. The next tuning experiment would be with EGT's. It would be nice to see how timing affects the EGT's. So my take on this is, if it doesn't need it, don't give it to it.