Yes Chrome, this is pretty confusing.

The speeds I posted above are for the Ha-45-21 engine equipped version. I believe this was a common version but I'm not sure.

I'm currently discussing with some reliable and knowledgeable people that I know through the IL2 flight sim community, because I'd like to have their numbers for Ki-84 top speed at sea level using war emergency power.

I believe that under these conditions, its top speed made an important leap, which could explain some reports, but I have no personal source, and I can't rely on internet finding on this subject (even in such a trivial domain as empty weight, you can find fairytales on the web lol).

Of course, it will not even get near of 664 kph, but I'm sure the gain, when compared to the "normal full throttle top speed" was important.

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Lemme know what you find out.

@ Chrome : I'll do, I feel the low level top speed at war emergency power could be far better than the specs at military power I provided above.

Your question is beyond my knowledge, I can only give a very rough operational story :

KI 84 Ia, first model to enter mass production, it mainly fought over China since march 1944 IIRC, facing the poor last USAAF P40s, then the Mustangs.

Ki 84 Ib, the most produced version, used since mid 1944 in the hottest spots of the Pacific theater : Philippines, Iwo Jima, Okinawa, then home defense. Maybe Mandchuria.

Ki 84 Ic : only a few were produced, used as an interceptor in home defense (mainly against B-29s)

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@ Chrome : ok, here's what I've been told about the performance of the Ki84 Ia in all out speed (war emergency power -WEP).

First of all, I've been told of the Japanese specification often did not take in account anything above military power, and that the Ki-84 Ia engine (21 version) supercharger settings caused a setback in performance as low as 2000-3000 meters.

In the other hand, the top speed increased in a quite linear way at 3.000 m and above, up until 6.000 m, and that's the reason why, under WEP, the Franck was faster than the P-51D between 5.000m and 7.000 m.

Now with some numbers : the Franck was still slower than the P-51D, but by a very slight margin (about 10-20 kph) below 2.000 m, both planes being little less than 600 kph fast à 0m.

Then the P-51D had clearly the upper hand, up to 4.500 m, with a large advantage (40 to 60 kph at about 4.000 – 5.000), but starting at 3.500 m and upper, it was turn to the P-51D charger to lack power and the gap narrowed.

They also confirmed more or less my above numbers about WEP in the 5.000 – 8.000 m altitude range the Ki84 was faster from 5.000 to 8.000 m, but starting from 5.500 m and above, the high altitude performance of the P-51's engine started to shine and speed incread linearly as altitude increased, up to 7.500 m, when the Ki-84 top speed decreased starting from 6.000 m. At 7.500 m, the P51 was about 30 kph faster.

I trust the few people i've disscused this subject with, and they have many times proven in the past they are really reliable when it comes to pacific theater planes, but I know it's not like if I came with a concrete undisputable reference.

Anyway, you'll probably admit that :

- it's quite credible to observe that the P-51D was only slightly faster up to 2.000 m, and such a difference is so thin, thant conditons as fuel load, plane's shape, engine tuning or whatever, could make the Ki-84 about as fast or even faster on some occasions,

- the performance drop of the Frank in the medium altitude range is very believable because of the task it was given,

- The Ki-84 was a monster in the 5.000m 7.000 range. For example it could compete with FW A8 and A9

- The Frank supercharger setting is quite comparable with late war Zero's settings (speed drop in the 2.500 m – 3.500 m range)

- It confirms in all points the often related Frank topspeed of about 680-690 at 6.500 – 7.000 m,

- It can explain some reports of P51 being unable to catch up with Frank, if the pursuit occured between 5.000 and 7.000 m.

- the Frank was not 2 mph faster than the Mustang at about 6.000 m but about 30 kph faster !!

Now I've also been infirmed in some affirmations I made above :

- the Frank was faster than the Georges and the Ki-100

- It's not quite sure wheter the Ki-84 Ib was more produced than the Ia version

- The Georges was better armored than the Frank (looks like I was wrong)

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Wow, thanks for posting that. Only point I would bring up was there were 2 heavily armed versions of the Frank. One had 4 20's & 2 machine guns, & the other had 2 20's 2 30's & 2 machine guns. These did pack more wallop than George.