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Theoretical question, all things equal.
If you had an engine that was 100% ve at 5k rpm/ 1bar and MBT is at 25 degrees.
Now if you upgrade part of the intake or exhaust and the engine becomes 105% ve at the same 5k/1bar.
Fuel is adjusted to achieve the same lambda. Does the timing of MBT change?
Theoretically yes. If you have greater cylinder filling, then the ignition should be less advanced as the combustion speed would be faster.
In reality there's more to it and it's not that simple.
In a lab environment with an instrumented combustion chamber the ignition timing is set to achieve peak cylinder presure at a particular crank angle. say 14 deg aTDC
MFB50/CA50 is another critical metric heavily influenced by ignition angle.
For a tuner on a dyno, you would tune for optimal timing with no knock.
It probably will change a little bit, most likely a little less timing advance for increased VE, but there are other factors that influence flame speed that can be affected by changes in intake/exhaust equipment.
What I have been noticing on my current project is the inverse being true...VE seems to improve as ignition advance approaches MBT. It is like there is a positive feedback loop between increased combustion pressure and improved scavenging across the valve overlap period is my best guess.
