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Neither throttle angle nor RPM form a linear relationship with fuel usage. You can't rely on a SG either because it doesn't account for varying volumetric effeciency differences on non-MAF engines, like the one I have.
Your engine actually pulls in less air per stroke at redline than at torque peak. Any formula that computes air consumed by MAP and RPM cannot account for this. If fuel consumption vs RPM were linear at WOT, you'd have a perfectly flat torque curve.
Also throttle angle is not a linear measure for fuel consumption. At low RPMs, it doesn't take much throttle to really raise manifold pressure. There isn't much difference between 40% and 100% throttle at 1500 RPM. This is because at speeds this low, it doesn't take much air to pass the throttle plate and fill the cylinders to a great degree. At 5000 RPM, the engine demands a lot of air, so it takes a significant amount of throttle to hit 5000RPM even in neutral.
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