Remember that the P40E did not have a manifold pressure regulator installed until sometime into late 1942/1943, therefore manifold pressure was regulated by pilot who used prop pitch and throttle to dictate boost. This was also true for all earlier P-40 variants.
Also note that full throttle height was around 11,000' ASL for 44" MAP, no ram.
This makes it different than just about any aircraft in the sim as there is no artificial hard upper limit to the boost. In other aircraft this limit was given by an automatic throttle actuator which interposed between the throttle lever and the carburetor, limiting maximum throttle movement to achieve up to the maximum boost level, regardless of further increases in throttle settings.
Rather, the upper limit was a matter of what the supercharger could deliver at a given engine RPM, throttle setting, and altitude - and what boost levels the engine could physically take without overt damage (which was given to the pilot by handbook, but which the pilot could at any time decide to disregard, as there was no mechanical limit to the boost beyond as noted above).
[edit]Attaching a file, which I'm quite sure you already have, showing power output for V-1710-39. Note that the maximum power (boost) possible at a given RPM and altitude is delineated by the upper dashed line, and is linear (can be extrapolated). This graph is largely similar for all Allison V-1710 engine variants used in the P40 C,D,E regardless of dash number - the only difference being the durability of the engine increased, the later the variant. This is what allowed the higher rated power (boost) levels from the V-1710-33 to -39 variants.
Sorry to belabor this point, but it is an important one.
F3R_power_chart.JPG
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