[Andyman]

Fuel consumption depends on more than just throttle position. Engine RPM is also very important. The intake air pressure and temperature and air/fuel mixture ratio are also factors. Fuel usage probably does not have a linear relationship with throttle position.

I made a crude formula to let you estimate the fuel consumption rate. It assumes an intake air temperature of about 100 degrees Fahrenheit and a normal air/fuel ratio.

GPH=D*RPM*VE*PA/18130

GPH: gallons per hour of gasoline used in engine
D: engine displacement in liters
RPM: engine revolutions per minute
VE: volumetric efficiency of engine which changes with throttle position
PA: intake air pressure in psi (about 14.7 psi at sea level)

The volumetric efficiency is a ratio of volume of air taken into the engine in one intake stroke to the displacement of one cylinder. It can be estimated by this formula:

VE=1-(VAC/PA)

VAC: intake manifold vacuum gauge reading in mm of mercury
PA: atmospheric pressure in mm of mercury (about 30 at sea level)

The actual VE will probably be lower than this because of the restriction of intake valves and exhaust gas recirculation which displaces some of the intake air. Operating the engine at speeds far away from the torque peak also lowers VE. Engines with a turbocharger or supercharger can have a VE greater than one. When idling or running without a load, the VE is usually near 0.30 or 30% but it varies according to compression ratio and valve timing.