There are many things that effect the ideal timing even between two motors running the same heads, like
Piston speed .
The rpm where the Cam gets into its max torque band.
Cylinder head temp increase during a pass.
The air to fuel ratio is a factor also.
Leaner mixtures take more time to burn the richest mixtures do.
This is where air density changes can drive you nuts if your trying to get a base line down.
So a lot of details have a hand in what the ideal timing might need to be for a given motor.
And even port velocity and the narrow rpm band where the tuned lenght Intake ramming takes place .
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