I dialed in the aggressive timing on the P-mags for testing this weekend. ?I really don't expect better performance from the additional timing advance. ?It should have a some additional timing advance with lower manifold pressures at higher altitudes or partial throttle operations (cruise flight) to help with fuel savings. ?Bear in mind that I operate from a high altitude airport, so can not pull more than 23.5 inches of MP, so expect some timing advance even during full throttle climb operations. ?I found that during climb out, my hottest CHT bumped up from 390 to 405. ?That is still acceptable, although on the cusp of what I am comfortable with running. ?As soon as I start dialing the throttle back a little, the CHT immediately drops as the throttle plate disturbs the air flow and the fuel mixes and distributes a bit better across the intake spider. ?#2 cyl has always been the hottest CHT under full throttle conditions due to an uneven fuel distribution at full throttle, so has become my measuring stick during climb operations. ?As soon as the throttle is reduced, the temperature drops into line with the other cylinders. ?During today's flight, under cruise conditions the CHTs ranged from 300 - 340*F across all 4, with only #2 (back left) running a bit warm during climb out.
The biggest issue was the oil temp during cruise flight. ?I was cruising with the cowl flap closed and 18.5" MP at 11,500'. ?Under those conditions, the timing curve should be fully advanced to 39*. ?My oil temp topped out at 220*F and stayed there under those (summertime) conditions. ?I was able to drop the oil temp back to 210* by opening the cowl flap, but that also induces a significant amount of drag, which is less than ideal for cruise flight. ?This is about 15 degrees warmer than the oil temp was running with the timing curve topped out at 34* under similar conditions. ?I am going to leave the timing dialed up while I explore ways to get a bit more cooling air directed at the oil tank (the O-200 does not have an oil cooler). ?If I can't get a little better results with the oil temps, I may have to restrict my timing advance to 34* during the summer months and dial up the timing for the fall and winter months. This and other write ups are located on my web site at <http://jeffsplanes.com> Jeff Scott Los Alamos, NM
