DIM Electronic Advance Ignition

An elegant approach. Since you have a plenty of processing capacity, you might think about adding knock detection to the unit. Hard to find a new car without a knock sensor.

Here is some info on DSP and knock detection. They cover the signal conditioning and implementation of knock control:

[ame="http://www.ti.com/lit/an/spra039/spra039.pdf"]http://www.ti.com/lit/an/spra039/spra039.pdf[/ame]

With the kind of timing accuracy you are aiming at, might as well make it do a cylinder by cylinder knock control too.

Good luck with your project.

B.