Scott,

Thanks for the information.  I took your numbers and did a crude reqression analysis and came up with the following:  The advance increases by 2.2 degrees per thousand rpm above 1700 and 0.85 degrees per inche of manifold pressure below 28.  Just gives a rough idea of how it works.

Gary

 

From Scott:

Restricting my comments to Lycoming engines (320, 360), one would note that 25 DBTDC is the fixed timing delivered by standard magnetos and that timing is adequate for a wide range of engine operations. My injected 320 engine has a 9:1 CR and uses a base timing of 20 DBTDC. Normal ROP cruise settings in the 4000 to 9000 MSL range and 2500 RPM (say 21 to 25 MAP), the timing is between 24 and 26 DBTDC. At takeoff and low altitude race power settings (2760 -2600 RPM, WOT, 28-30 MAP), the timing is about 22-23 DBTDC. At leaned idle/taxi power (<10" MAP, <1100 RPM) the timing is about 34-35 DBTDC. At altitudes 10000- 14000 MSL, 2500 RPM, WOT and LOP the timings are generally 29-31 DBTDC.

Scott Krueger