The possibility that Steve suggests below is probably real, but remember that the electronic ignition will only advance when the manifold pressure - and hence the cylinder pressure - is lower than the max (only at high altitude or part throttle).  And the electronic ignition will only advance 5 or so degrees more than the mag anyway.  In 5 or 10 degrees the cylinder pressure will not rise much. 

Gary,

 

Because I am running at a 9:1 CR, my base timing is 20 dBTDC.  Light Speed EI recommends that 20 dBTDC base timing for engines operating with CRs greater than 8.7:1.  At 80% to 110% my timing is less than 25 dBTDC.  At 25**2 the timing is right around 25 dBTDC.  At race power, 2750 RPM, 30" MAP, I typically see 21 or 22 d BTDC.  At low power settings enforced by high altitudes, thus reducing my WOT MAP, I see 28-30 dBTDC or so.  At idle power settings, say 10-12" MAP, 900-1100 RPM, I generally see 34+ dBTDC.  It all works out very nicely.  That means my timing span is as much as 34 degrees, depending. 

 

I did a great number of experiments with the LASAR ignition where I would fail the EI in flight, reverting to the fixed timing mags and compare the results.  Too bad I didn't have any timing data on the EI function.  Also, note that I now use the LSE (Light Speed) EI system.

 

PS: Colyn, FYI see LSE timing data listed above.