In article ,
wrote:

Another little tidbit on this idea is to wait for a little bit
before energizing the alternator field (with split master). The
alternator actually presents a fairly significant amount of torque load
when putting out full output, which it does briefly when flipped on after
starting. I generally wait until the oil pressure has built up and
stabilized for a bit before flipping on the alternator and watching the
ammeter spike.

In planes with a split master, I generally leave the alternator off
during starting. I figure between the field drawing current and the
alternator shaft presenting a torque load, having the alternator on
while cranking will just make it harder to start.

Of course, I have no real numerical data to quantify either of these
effects, so the above is all pretty unscientific.