@ Chrome : I heard about this test, they used US fuel in the Frank , which was very different from Japanese fuel, and probably pushed the plane beyond its specifications.
About this test, I find no data about low and medium altitude speed, only a 427 mph at 20.000 feet, and neither I know if the tested Frank was a Ia version and what engine it carried.
Have you got a link toward a comprehensive report of this test, especialy the speed reached by the Frank at low or medium alt ?
Because 20.000 feet is not a low altitude and it's right into the altitude fork where the P-51D (D-20) had a weakness due to supercharging staging (I believe) and was the very peak of the Ki-84Ia top speed, therefore I won't draw conclusion on this sole altitude.
Here we go
Altitude / P 51D20 speed / Ki84 Ia speed(meters / kph – metric system rules ! ) : no war emergency power
1000 560 / 520
2000 605 / 550
3000 630 / 560
4000 655 / 570
5000 645 / 600
6000 630 / 630
7000 650 / 645
8000 680 / 630
Now, let's tighten the fork to the only altitude range where the Ki-84Ia (war conditions) could compete with the P51-D, the 5.000 – 8.000 m range, at "all out" speed (which means "overboost", war emergency power etc etc)
5.000 665 / 660
6.000 660 / 685
7.000 690 / 680
8.000 700 / 670
As you can see, these numbers are pretty much on par with the above mentionned bench, rating the Frank at 427 mph @ 20.000 ft, but still the P-51D is faster at low alt (below 3.000m and medium alt (3.000 – 6.000 m).
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