Help! I need a little clarification on THE proper mag timing for a straight-up 112, IO-360-C1D6 engine. The Maintenance Manual says 25 deg BTC.  The FAA 1E10 type certificate says 25 deg, optionally 20 degrees.  My engine data plate is stamped over with both 20 & 25. My timing is set at 20.

Does anyone know the circumstance under which you would want to use 20 instead of 25. Should I be set at 25?

Thanks,
Ken/N1032J/ROA
112 Ser#0032