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FS2004 Fuel flow at different Mach speeds

I came across some performance chart for a 747-100 & 747-200 with the -7A and -7J engines. So I loaded up the RFP 747 and messed around with the air file to kinda match what I could to get a similar performance.

What I found is that the difference of fuel flow between difference each Mach speed - 0.82, 0.83, 0.84, 0.85 is far greater in the sim that the real charts.
For instance, if I get an accurate fuel flow at FL330 and M0.84, then its far too high at 0.85 and far too low at 0.83. Perhaps 2-3 times the difference compared to the real chart.
I couldn't see any way at all to change that with my limited knowledge of air file adjustments.

Is there a way to do get this a little more accurate?
Any help greatly appreciated.
What you are seeing is the effect of drag variation with Mach. If your fuel consumption rate is too high at a specific Mach number it is because the drag is too high.
Since FSXA you can vary the interval between adjacent Mach drag values and fine adjust the transonic drag. Unfortunately, you cannot do that in FS2004, you are stuck with zero lift drag coefficient values at 0.2 Mach intervals. So you will have a value for 0.8 Mach and the next value is for 1.0. You will have a linear variation when in fact it is very non-linear in that Mach bracket.
Yeah thought there was some catch. Frustrating. But I guess I'll just work on having fuel flow being correct at a standard cruise speed of 0.84 and accept 0.85 fuel flow being too high and 0.83 too low.

Those crazy programmers. :p

Appreciate the reply