Went up this morning to do some high altitude testing and finally try out the oxygen setup. Went very well. The cloud bases were at 5500, the tops at 7500. It was clear in the early morning, but had become scattered to broken by the time I went up at 11. Refueled first, and with ~40 lbs of baggage I was flying at 1500 lbs.
Got up to 8500, set a course at 350, turned on the autopilot and donned the oxygen mask. I have a finger tip pulse/oximeter and used it all during the testing. After leaning the engine I did several cruise measurements, max power, then for 55% power recorded outside temp, manifold pressure, RPM, indicated airspeed,true airspeed, and fuel flow. Then monitored blood oxygen. With oxygen on, I never saw oxygen saturation go below 98%. Then commanded the autopilot to a 400fpm climb, added a bit of power, and went up 1000 ft.. Turned to a 010 heading to keep my heading correct for the cruise altitude of 9500 ft. Then recored the data and monitored oxygen. Repeated this process for up to 14,500 feet. After that, I did a short excursion up to 15000 just to say I did it.
The OAT at the surface was upper 80's, and the pressure at Lago Vista was 30.06 (inches mercury), so density altitudes were about 2000 feet higher than true altitudes. On the way back down, at 11.5, I turned off the oxygen. In about 5 minutes, blood saturation was down to 92%. It's clear that the oxygen system does what it's supposed to! I had to get down to 8500 to get the reading back up to 95%.
It was a fairly nice day at 3R9.