Here's some data from my SERG/Franklin/IVO GPH 9 8 9.1 TAS 172 170 173 ALT 8500 12500 7500 OAT 56 44 75 Load 500 410 311 RPM 2610 2580 2630 Load = fuel + pilot + luggage The first two data were taken on the same flight. Interestingly, when I climbed to 12,500, I didn't change the mixture. John