Report No. F-1IM-1119B-ND of flown refurbished Ki-84s in the US in 1947 states similar speeds as the TAIC study, so their estimations were pretty accurate to the performance of a “perfect” ki-84.
Also war thunder does not use historical or test sources, they mostly use estimates and theoretical performance, Gaijin picks and chooses when they feel like it, historical accuracy is not a rule for them, but “realism” is. Just look at the plane after the KI-84, the Kikka got its historical engines replaced by more powerful engines that were never built and has an estimated speed that is very questionable.
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Since the captured Frank have only ran with +350mm, this performance figure F-1IM-1119 you’ve mentioned was a direct citation from the TAIC estimation in March 1945. The number fits the TAIC estimation so precisely which couldn’t be a spec from test flight.
Just compare the number and you will find they match exactly. Thus confirming it was a citation instead of actual record.
The actual test flight in 1946 was recorded, the maximum power been used was +340mm, instead of +500mm estimated in the TAIC figure:
They did tried to run Homare with +500mm TO power in the engine test(not with the plane), but the cylinder head temp rose up to 300 degree Celsius which exceed the 260 deg limit within 3min.
Another TAIU test in 1945 have been cited by me previously, the Ki-84 with +250mm MIL rating only achieved around 580kph at 6000m:
Another Japanese doc listed Ki-84 with +250mm power setting to have 615kph@7000m. Still far behind any claim of 680kph.
The only reference possibly for a ‘PERFECT’ Ki-84 utilizing +500mm and thrust exhaust nozzle happens to be in an American report stated “There is a Japanese report showing Ki-84 otsu running 660kph”. Unfortuneatly no one ever saw that report ever since that quote.
Closest Japanese Doc for a ‘PERFECT’ Ki-84 by far:
The doc listed ki-100 (Type 5 fighter) to have 660kph maximum, but clearly there’s no way for a Ki-100 to achieve 660kph. It could be a TYPO that the doc was listing ki-84(Type 4 fighter), and could be the source that was mentioned by the American report.
Since the Ki-44 in the doc is 30kph faster than in the manual, it should be using the TO power, or WEP. Thus we can infer that the ‘Ki-84’ in the doc was running 660kph using +450/500mm TO power, and it is also 30kph faster than in the manual. Which fits the calculation by the thread owner. However this doc is still quite uncomplete and have never answer whether those figures were from calculation or actual test flight.
Even with this performance, the Ki-84 in the game is still 30kph faster than in history.
