Genarally speaking, for turbo and non-turbocharged piston engines, figure...one half pound of fuel per HP per hour.
Again, generally speaking, the
only exception to this was with the CurtisWright R3350 DA/EA series turbo
compound piston engines which had three Power Recovery Turbines (exhaust driven) fitted, which provided extra power
directly to the crankshaft via fluid couplings. With these engines, the fuel consumption was (approximately) .36 pounds of fuel per HP per hour.
However these engines, in order to be operated as designed
absolutely required 115/145 avgas, generally not available today.
The longest range piston engine airliner was fitted with these very advanced engines, the Lockheed 1649A Constellation.
23 hours endurance....provided you did not run out of oil.
A superb aircraft.
