just got a new GTN 650/345 installed...and i flew it today...and looked down and noticed i was 'burning 14.5gph at 2400/24 on the G3X...yikes. i sure hope its an error in the calibration...engine has 200hp...
looks like ill get to fly some more and see it thats real...175K GS..
Marlon, we can help you get dialed in, if you supply the necessary information.
(1) Gallons per hour is a data point, but as the others have noted, we also need some idea of mixture state. That means referencing EGT to peak EGT in degreesF lean or rich of peak, or at least a notation of "Full Rich", or "Best Power" (ballpark 100~125 ROP).
(2) Calibrate the
true airspeed indication on the GX3. That means flying some NTPS 3-leg runs to gather data. Download the "GPS PEC spreadsheet" at the link below. The inputs are groundspeed and
track (not course or heading).
http://www.ntps.edu/information/downloads.html
(3) Need some idea of altitude. Generally max speed is found down low, max efficiency up high.
Is this stuff important? If we assume the reported groundspeed (175 knots) is your actual true airspeed, and 14.5 GPH is your best fuel burn to achieve that speed, well, your RV-8 looks like a pig.
Yes, I'm pulling your chain. However, there is room for improvement. Here's 70% on an IO-390, best power mixture (note EGT indications between 105 and 125 rich of peak). I had the power turned up more than usual, as we were bucking a 32 knot headwind, and I'd told friends a specific arrival time. True airspeed is 194 knots, on 12.4 gph, at near gross weight.
Here is roughly the same speed (175 vs 178) on roughly
half the fuel burn, running up high and 25~30 LOP.