Oh boy.
This is going to sound real bad of me, but as far as the "magic number" goes, it is ALL dependent on so many things.
EOT plays a HUGE role in start of injection.
The SOI map is simply based on Mass Fuel Desired vs. Engine speed................
There's a map for an adder based on those but for low boost...............
There's a delay map that factors in the electrical/mechanical delay inherent in the injectors....................
The injection control pressure has an effect on the actual start of combustion........
Physical combustion chamber temperature has the same effect...............
Boost pressure (dynamic compression) has a similar effect on speed of flame travel......
Backpressure seems to have an effect as well...............
There are far too many variables to put a "magic number" in for any particular engine. Every engine is going to be different for a maximum or "sweet spot".
As for the ability to tell how much is too much; a trained ear can hear it but you probably don't want to hear it very long before fixing it. It sounds terrible...like marbles in a barrel at extremes.
Good luck.
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Tuning, flashing, burning chips, and repairing all aspects of 7.3L Powerstrokes.
SEVEN 7.3L-powered vehicles in the driveway. Two didn't come that way from the factory!
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