I don't know if it's different in FSX, but the startup and shutdown in FS9 seem a little too quick for such a huge set of cabbage choppers, so I set about to find a bit less "snappiness." I added one line and adjusted two others as follows, and I'm quite happy with the results:
If you reduce the starter torque any further, you'll have to start the engines manually with the M > +++ method. The Sim just won't hold the starters engaged long enough.[fltsim.x]
prop_anim_ratio=0.5
[piston_engine]
normalized_starter_torque = 0.0065
[propeller]
propeller_moi = 250.0