FWIW
180 hp M20C (carb'ed) run 600 hrs mostly x-c at 75% 9.5-10 gph cruise
trips of 1.5-2.5 hours typical
Flight Fuel Flow average 9.1 gph (total fuel / flt time) as measured
by Garmin 196
Tach Fuel Flow average 8.5 gph (total fuel / total tach)as measured by
Horizon electronic tach
No Hobbes to compare
YMMV



Rule of thumb for piston engines: divide rated HP by 18 to get cruise
fuel flow. Assumes about 75% power and proper leaning.
IE, 230 HP is about 12.7 gal/hr.