Just want to add to this my comments, given the link to my thread.
Any intake, exhaust, or other significant change to the stock engine layout will change the volumetric efficiency, thermal efficiency, combustion flame speed(due to fuel density etc), static and dynamic compression ratio etc along with many other things. All of these changes effect the required ignition advance for maximum efficiency and power.
This in my opinion should drive anyone to look at custom ignition curve mapping, even more so when the cost to do it can usually be considered minimal compared to the overall engine build cost.
Going to electronic advance control is not the only method; changing advance weights, springs and stops in distributors is also a suitable method but can result in less than ideal timing at some points within the working RPM range of the engine.
Crank fired systems will give timing with the least fluctuation as there will be no play between the firing trigger and the actual crank rotation, however the amount of fluctuation in the distributor drive is likely to be less than 1 degree in most decent engines with a good distributor. There's some posts about this on a Porsche forum somewhere to back this up.
1 degree of fluctuation in a road going engine is negligible, as we allow for it some conservative setting of the ignition timing anyway. 1 degree of fluctuation only becomes relevant on engines running on the ragged edge of detonation like drag cars and such.
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