What is it that you want to change ?

I think I'm following you here. I set out to make my C210P (available here at Simviation) fly as realistically as possible.

For fuel flow.. it was a combination of tweaking the fuel-flow scalar in the aircraft.cfg file and then re-doing the fuel-flow gauge bitmap, for more accurate scaling, green arc, etc. (I used the FF gauge from the C182).

For manifold pressure it was similar. Turbo charging and then setting max MP to 30 (turbo normalized)  in the aircraft.cfg file and then re-doing the bitmap for the MP gauge.

Max RPM is another thing that is first controlled in the aircraft.cfg file and then suitably matched to a tachometer/bitmap.

NOW.. the one roadblock I found, is that the FS9 fuel flow data is more like info for a make-believe, hybrid FF/EGT gauge. Leaning at altitude will first yield a fuel-flow increase (like an EGT gauge peaking). Realizing that we're talking about a very comlex, custom XML gauge, I gave up and settled for reasonably accurate, cruise fuel flow, at any altitude.. regardless of the bizarre, too rich to too lean spike.