N1K2-J Shiden-Kai Performance

[CORSNING]

My question would be; The numbers for the first 180 degrees of the turn
indicate that the propeller is turning CCW (from the cockpit). The second
half of the turn indicates even more torque in the opposite direction.

Direction: 1st 180 / 2nd 180 degrees
Right: 8.55 / 11.45 seconds
Left: 9.15 / 7.9 seconds

Is this even possible?

 

[Ivan1GFP]

Hello Corsning,

I believe that this IS possible if the Engine Thrust Line is not coaxial and aligned with the axis of the airframe.
This kind of thing was done on the Bloch fighters, the F8F Bearcat and of course the BV 141 in the extreme case.
Of course there is also the possibility (though not in this case) of the Propeller rotating in the opposite direction.
There are also probably a couple ways that this could be done aerodynamically, perhaps by having one wing longer than the other as was done on the Macchi fighters. At high speed and low AoA, this might not be as noticeable as at low speed and as these turns progress, the speed gets lower and AoA MAY be getting higher.

- Ivan.

 

[Ivan1GFP]

There are many misconseptions and confusions regarding the real performance of this fighter. If you look at the Specification of performance of IJN Fighters table from 10th september 1945, or US TAIC for George 21 or sources like Francillon. They all state the Performance of the N1K2-J was 595km/h at 5600m and 7:22 to 6000m rate of climb.

But they are wrong. Its not feasable and my only explanation to those performance figures is if it had a big external fuel tank under its fuselage which wasnt uncommon for it to mount.
Why are these figures not believable?
N1K2-J has 3800kg loaded weight and a Ha-45-21 (1990hp engine)
Ki-84 has 3600kg loaded weight and uses the same Ha-45-21 (1990hp engine)

Ki-84 with Ha-45-21 had top speed of 674km/h (687km/h according to US TAIC calculations)
It could climb to 6100m in 5:48 (from US TAIC)

Hello Laurelix,

Over the last few days, I have been reviewing the data I have collected on the N1K2-J and while I agree that the aircraft is a lot faster than the typically quoted 369 MPH (595 KPH), I don't entirely agree with your reasoning.
First of all, the TAIC may have listed the "George 21" at 369 MPH, but in one note that was reproduced in a collection of TAIC reports, it is also listed as 416 MPH @ 19,028 feet (669 KPH @ 5800 meters).

My belief is that the actual number is somewhere in between but much closer to the 416 MPH number.
Hopefully this is a chance for everyone to re examine what data we have and see how it fits together.

There is literally only 200kg weight difference between the two planes and we can see such huge difference in the rate of climb, nvm the top speed. Why would this plane with much better power to weight ratio compared to an A6M3 have a rate of climb worse compared to an A6M3? It makes no sense. Those performance figures just have to be with external fuel tank adding drag and the weight of it is definitly over 3800kg.

There is actually much more than just a 200 kg difference between these two aeroplanes. Besides general size and sharing the same engine, there are many detail differences that would affect maximum speed.

On the first image youll see a left and a right hand side with performance figures.
On the right hand side are the actual japanese flight tests results on the Prorotype N1K2-J which was using derated Ha-45-21 since the engine was suffering issues at the time. It achieved 611km/h at 6000m at military Power and it could climb to 6000m in 6:20 at military power. On the left hand side are the japanese estimated performance values for N1K2-J once the engine is running at its full 1990hp power setting, however its overoptimistic since the engine didnt have as much power at 6000m as they thought it would. They estimated 644km/h at 6000m at military power and 5:15 to 6000m at military power. The actual performance would be about 628km/h at 6000m at military power and 5:30 to 6000m at military power. At WEP the top speed would be about 652km/h

As you can see now it actually looks believable.
Top Speed: (WEP)
N1K2-J - Roughly 652km/h
Ki-84 - Roughly 672km/h

It's unsurprising the final result shows only 20km/h difference in top speed between N1K2-J and Ki-84 when both are using full power Ha-45-21 (1990hp) engine because
N1K2-J with de-rated Ha-45-21 engine achieved 611km/h at 6000m whilst Ki-84 with the same de-rated engine achieved 631km/h at 6000m at Military Power.

There are many problems with the table that you posted.
First of all, although this was a derated Ha-45-21 with SIMILAR power to the Ha-45-11, it wasn't really a Ha-45-11.
The -11 and -21 differed in maximum RPM, maximum manifold pressure and possibly a few other things.

As for the fully rated Ha-45-21 not making the level of power that was expected, the ones tested by the TAIC and notably the one tested at Middletown was able to equal or exceed most of the power specifications.

One other thing worth noting is that these tests were corrected for 6000 meters altitude while the actual critical altitude for military power for this engine was 6500 meters. That would suggest that if there is any significant ram effect at all, the maximum speed should be achieved at a slightly higher altitude. For the Ki 84, this altitude at military power is listed as 7000 meters. I suspect this also to be the case for the N1K2-J.

Note:
Taic used calcaulations to state Ki-84 top speed. the drag coefficient is a bit overoptimistic. I used the japanese Ki-84 manaul which states 624km/h at 6000m at military power top speed using the Ha-45-11 (1800hp) engine which is what the early Ki-84's had. 1460hp at 5700m = 624km/h at 6000m. With 1625hp at 6000m using this same drag coefficient gives you about 648km/h. At WEP youre looking at about 672km/h

I would have to agree with you that the numbers here do not seem to fit together. The only thing I can think of at the moment that makes sense is that the 624 KPH (388 MPH) @ 6000 meters is correct but that the actual maximum speed for the Ki 84 at military power was greater than that and achieved closer to 7000 meters.
At J-Aircraft there was mention of captured documents listing the maximum speed of a Ki-84 (Improved) at 688 KPH (427 MPH) with a fully rated Ha-45 and with a power output equivalent to what was achieved by Middletown at WEP rating (1800 HP). This suggests to me that the TAIC speed estimate for Ki-84 had some corroboration.
The military power listing you might want to try is 1700 HP (metric) at 6400 meters or 1676 HP.

Now back to the N1K2-J:
Another hint that the N1K2-J might be a bit faster is that the TAIC test of a N1K1-J listed a speed of 408 MPH @ 20,000 feet. According to the graph, speed at Military power is around 407 MPH @ 21,500 feet.
The N1K2-J had an improved and more streamlined cowl and also did not have the two underwing cannon pods.

As for similarity to the Ki-84, the N1K2-J actually had a slightly shorter and deeper fuselage. The wing span was greater and there was about 2.5 meters^2 more wing area. The airfoil used was also different. Although the engines were the same, the propeller was considerably bigger for the N1K2-J.

Firepower:
4x 20mm Type 99 Mk 2 (225 rounds per gun)

The actual ammunition loads were 200 round for each inboard gun and 250 rounds for each outboard gun as compared to the 150 rounds per 20 mm cannon for the Ki-84.

- Ivan.

 

[Laurelix]

Hello Laurelix,

Over the last few days, I have been reviewing the data I have collected on the N1K2-J and while I agree that the aircraft is a lot faster than the typically quoted 369 MPH (595 KPH), I don't entirely agree with your reasoning.
First of all, the TAIC may have listed the "George 21" at 369 MPH, but in one note that was reproduced in a collection of TAIC reports, it is also listed as 416 MPH @ 19,028 feet (669 KPH @ 5800 meters).

My belief is that the actual number is somewhere in between but much closer to the 416 MPH number.
Hopefully this is a chance for everyone to re examine what data we have and see how it fits together.



There is actually much more than just a 200 kg difference between these two aeroplanes. Besides general size and sharing the same engine, there are many detail differences that would affect maximum speed.



There are many problems with the table that you posted.
First of all, although this was a derated Ha-45-21 with SIMILAR power to the Ha-45-11, it wasn't really a Ha-45-11.
The -11 and -21 differed in maximum RPM, maximum manifold pressure and possibly a few other things.

As for the fully rated Ha-45-21 not making the level of power that was expected, the ones tested by the TAIC and notably the one tested at Middletown was able to equal or exceed most of the power specifications.

One other thing worth noting is that these tests were corrected for 6000 meters altitude while the actual critical altitude for military power for this engine was 6500 meters. That would suggest that if there is any significant ram effect at all, the maximum speed should be achieved at a slightly higher altitude. For the Ki 84, this altitude at military power is listed as 7000 meters. I suspect this also to be the case for the N1K2-J.



I would have to agree with you that the numbers here do not seem to fit together. The only thing I can think of at the moment that makes sense is that the 624 KPH (388 MPH) @ 6000 meters is correct but that the actual maximum speed for the Ki 84 at military power was greater than that and achieved closer to 7000 meters.
At J-Aircraft there was mention of captured documents listing the maximum speed of a Ki-84 (Improved) at 688 KPH (427 MPH) with a fully rated Ha-45 and with a power output equivalent to what was achieved by Middletown at WEP rating (1800 HP). This suggests to me that the TAIC speed estimate for Ki-84 had some corroboration.
The military power listing you might want to try is 1700 HP (metric) at 6400 meters or 1676 HP.

Now back to the N1K2-J:
Another hint that the N1K2-J might be a bit faster is that the TAIC test of a N1K1-J listed a speed of 408 MPH @ 20,000 feet. According to the graph, speed at Military power is around 407 MPH @ 21,500 feet.
The N1K2-J had an improved and more streamlined cowl and also did not have the two underwing cannon pods.

As for similarity to the Ki-84, the N1K2-J actually had a slightly shorter and deeper fuselage. The wing span was greater and there was about 2.5 meters^2 more wing area. The airfoil used was also different. Although the engines were the same, the propeller was considerably bigger for the N1K2-J.



The actual ammunition loads were 200 round for each inboard gun and 250 rounds for each outboard gun as compared to the 150 rounds per 20 mm cannon for the Ki-84.

- Ivan.

the TAIC reports are all calculations with made up drag coefficient. for example it states 650 max speed for J2M2 and 671 for J2M3 eventhough they used the same engine and J2M3 was draggier. Furthermore the actual top speed at WEP for J2M2/M3 was more like 613km/h. My N1K2-J top speed is calculated based from actual N1K2-J test flight using less horsepower.

 

[Ivan1GFP]

the TAIC reports are all calculations with made up drag coefficient. for example it states 650 max speed for J2M2 and 671 for J2M3 eventhough they used the same engine and J2M3 was draggier. Furthermore the actual top speed at WEP for J2M2/M3 was more like 613km/h. My N1K2-J top speed is calculated based from actual N1K2-J test flight using less horsepower.

Hello Laurelix,

I don't think you understood what I was trying to tell you in the thread about the Raiden.
Yes, the J2M2 and J2M3 used the same engine.
If you look at the power curves for the engine you will find that the maximum speed of J2M2 was achieved with the equivalent of Military Power. (Check the Altitudes and where they plot on the Graph.) I KNOW what it says in the report but the numbers do not match up with other data about the engine.
The J2M3 speed was actually done at an altitude at which it actually DID have additional boost available for "War Emergency Power".
Why do you think the J2M3 was draggier than J2M2? The J2M3 gained a flush mounted cannon in each wing but deleted a gun port on each side of the cowl. It seems to me that if anything, the J2M3 would be the cleaner aircraft but the difference would be pretty minimal.

The first problem as I was pointing out with your "Test Flight of N1K2-J" is that it was with an engine that was not fully rated but was not necessarily the equivalent of a Ha-45-11.
The second problem is that the critical altitude of the Ha-45-21 is actually 6400 meters and not 6000 meters.
With a bit of ram effect, an aircraft critical altitude of 7000 meters is much more likely than 6000 meters.
What happens when you raise the critical altitude by 1000 meters?
The test of the Ha-45 at Middletown, I believe, is pretty good indication that the output of a well-maintained Ha-45-21 was well within the capabilities of the claims made for the engine.
In other words, on some of the tests, engine output may not have reached expectations, but eventually things were straightened out well enough to reach projected figures.

Hiromachi had a pretty good discussion about the speeds of N1K2-J on one of the other boards and while I don't agree with all the conclusions, the arguments are pretty well reasoned.

- Ivan.

 

[windswords]

I think the high figures for the Ki-84 speed (670-680 kph) in the OP are based on false data. This is covered in an old thread: Ki-84/Homare in the U.S.

To partially quote: "In the original TAIC manual from Dec.44, the performance was estimated at 422 mph. This was based on the assumption that the lines were similar to OSCAR. Then, in the March 1945 TAIC supplement, the performance was updated to the 427 mph figure. By that time, they had found some aircraft along with some documentation. The aircraft were not flown in the Philippines until the summer, however, so these performance figures are NOT based on any flight test that the US made, but most likely originated from captured japanese documents".

If those speeds were not achieved and the more accurate 388-394 mph (depending on engine model) are taken into consideration then the gap between the N1K and the K-84 mentioned in the OP is not that wide when you factor in difference in weight and less drag of the Ki-84.

 

[Laurelix]

I think the high figures for the Ki-84 speed (670-680 kph) in the OP are based on false data. This is covered in an old thread: Ki-84/Homare in the U.S.

To partially quote: "In the original TAIC manual from Dec.44, the performance was estimated at 422 mph. This was based on the assumption that the lines were similar to OSCAR. Then, in the March 1945 TAIC supplement, the performance was updated to the 427 mph figure. By that time, they had found some aircraft along with some documentation. The aircraft were not flown in the Philippines until the summer, however, so these performance figures are NOT based on any flight test that the US made, but most likely originated from captured japanese documents".

If those speeds were not achieved and the more accurate 388-394 mph (depending on engine model) are taken into consideration then the gap between the N1K and the K-84 mentioned in the OP is not that wide when you factor in difference in weight and less drag of the Ki-84.

Japanese N1K2-J Prototype achieved 611km/h at 6000m with derated Ha-45-21 engine.
Ki-84 with the same derated Ha-45-21 engine achieved 631km/h at 6000m

 

[DarrenW]

f those speeds were not achieved and the more accurate 388-394 mph (depending on engine model) are taken into consideration then the gap between the N1K and the K-84 mentioned in the OP is not that wide when you factor in difference in weight and less drag of the Ki-84.

A quote from Aero Detail 24: Nakajima Ki-84 Hayate "Frank" (Japanese publication):

"...although "official" data on the Ki-84 indicated a top speed of 624 km/h, in practice the aircraft really could only reach 580-590 km/h."

So rather than discussing theoretical performance figures based on drag coefficients or with unobtainable high octane fuels we should be trying to focus on the ACTUAL performance of front-line aircraft as this is what JAAF pilots had at their disposal when they were pitted against allied pilots in Mustangs, Thunderbolts, Hellcats, Corsairs, and Lightnings.

 

[taly01]

Japanese N1K2-J Prototype achieved 611km/h at 6000m with derated Ha-45-21 engine.
Ki-84 with the same derated Ha-45-21 engine achieved 631km/h at 6000m

I have noticed alot of other Japanese aircraft tests are at 6000m, while these also don't appear to have critical supercharger altitudes at 6000m. I suspect the "required performance contract" ? specified 6000m so that is what they tested at.

"...although "official" data on the Ki-84 indicated a top speed of 624 km/h, in practice the aircraft really could only reach 580-590 km/h."

Also its likely the prototypes and high speeds quoted were for planes without bomb racks and claws, from earlier research I did bomb racks cost ~20kph for any plane.

 

[DarrenW]

Also its likely the prototypes and high speeds quoted were for planes without bomb racks and claws, from earlier research I did bomb racks cost ~20kph for any plane.

Interesting. Through your research were you able to determine if the prototypes for the N1K2 and Ki-84 had their full compliment of pilot protection and armament?

 

[Peter Gunn]

I got to see a Shiden Kai in the Pensacola Naval Air Museum a few weeks ago. Beautiful aircraft.

Eye of the beholder I guess, its looks don't do much for me, reminiscent of the svelte A6M after one too many wagyu steaks. It's not ugly but not (to me) beautiful.

Again, just my personal opinion on its looks, not performance.

 

[DarrenW]

Eye of the beholder I guess, its looks don't do much for me, reminiscent of the svelte A6M after one too many wagyu steaks.

So sort of like a full-figured version of the Zero lol. I can see that.

 

[Peter Gunn]

So sort of like a full-figured version of the Zero lol. I can see that.

Let's just say... "Plus size" and leave it at that...

 

[Laurelix]

Ki-84 achieved 624km/h at 6000m at military power using Ha-45-11 engine.

The late war Ki-84's used Ha-45-21. Anyways... if Ki-84 could do 624 at 6000m at military with Ha-45-11, with Ha-45-21 at WEP it should do 674km/h using same drag coefficient and propeller efficiency.

 

[DarrenW]

Ki-84 achieved 624km/h at 6000m at military power using Ha-45-11 engine.

The late war Ki-84's used Ha-45-21. Anyways... if Ki-84 could do 624 at 6000m at military with Ha-45-11, with Ha-45-21 at WEP it should do 674km/h using same drag coefficient and propeller efficiency.

When did the Ki-84 actually achieve 674 km/h? If possible please provide date(s). And do you believe that the average Ha-45 could produce it's factory rated horsepower on WWII period Japanese fuels? From what I gather it was common place to use ADI just to obtain anything near take-off and military power, that's how bad their avgas really was. Beside the fuel issue, this particular engine required a great deal of care in construction and in-field maintenance which hampered it's reliability greatly as the war progressed.

Taly01 mentioned that bomb racks cost the Ki-84 approximately 20 km/h. Add in a multitude of late-war manufacturing defects and aforementioned engine issues and one can see that even 590 km/h would be on the optimistic side of things.

 

[Laurelix]

When did the Ki-84 actually achieve 674 km/h? If possible please provide date(s). And do you believe that the average Ha-45 could produce it's factory rated horsepower on WWII period Japanese fuels? From what I gather it was common place to use ADI just to obtain anything near take-off and military power, that's how bad their avgas really was. Beside the fuel issue, this particular engine required a great deal of care in construction and in-field maintenance which hampered it's reliability greatly as the war progressed.

Taly01 mentioned that bomb racks cost the Ki-84 approximately 20 km/h. Add in a multitude of late-war manufacturing defects and aforementioned engine issues and one can see that even 590 km/h would be on the optimistic side of things.

Those figures are achieved when its using 92 octane fuel + Water/Methanol injection

N1K2-J (92 octane fuel)
628km/h at 6000m - 1625hp
652km/h at 6000m with W/M injection - 1810hp

Ki-84 Ha-45-11 (92 octane fuel)
624km/h at 6000m - 1450hp
647km/h at 6000m with W/M boost - 1615hp

Ki-84 Ha-45-21 (92 octane fuel)
650km/h at 6000m - 1625hp
674km/h at 6000m with W/M Injection - 1810hp

 

[DarrenW]

Those figures are achieved when its using 92 octane fuel + Water/Methanol injection

N1K2-J (92 octane fuel)
628km/h at 6000m - 1625hp
652km/h at 6000m with W/M injection - 1810hp

Ki-84 Ha-45-11 (92 octane fuel)
624km/h at 6000m - 1450hp
647km/h at 6000m with W/M boost - 1615hp

Ki-84 Ha-45-21 (92 octane fuel)
650km/h at 6000m - 1625hp
674km/h at 6000m with W/M Injection - 1810hp

I'm sorry but of your figures are extrapolations and not based on any type of real world testing. Plus using ADI normally lowers FTH so having 6000m for both boost settings (+350mm/+500mm) cannot be correct.

I am also certain that aerodynamic drag doesn't remain linear as speed increases so I'm skeptical that it can be used to accurately determine what speeds are attainable for a particular aircraft with any given horsepower. Same with propeller efficiency, as it also varies with RPM and air density.

So until I see more empirical data on this I would tend to agree with Hiroyuki Takeuchi concerning the Ki-84, who posted this information on the J-Aircraft website:

The Ha45 was designed to use 100 octane or at least 92 octane fuel but most IJA fuel was around 87 octane and probably even worse towards the end of the war. That means the motor had to be run on less boost and less power. Since the engine quality and airframe finish were also suffering, that all reflected upon performance. Writer Minoru Akimoto mentions that some Hayates in service conditions were lucky to achieve 600km/h (370mph). No wonder the 580km/h (360mph) Ki100 is often touted as the being better than the Ki84.

So while the Ki84 design had a 420mph potential, elements of reality (poor fuel, faulty engines, rought airframe finish, etc) often limited its performance to a lower level. May be the 624km/h (388mph) figure is about right after all.

Source: Ki-84 performance...so which is it? (Return to Faq)

And as far as the performance of the N1K2 is concerned, when taking into account different aircraft conditions and actual flight test data I suspect that maximum speed could vary around 20 mph (350-370 mph). A wartime maximum speed of 652 km/h (405 mph) is complete fantasy and shouldn't be considered as anywhere near the actual figure attainable during the war.

 

[Laurelix]

I'm sorry but of your figures are extrapolations and not based on any type of real world testing. Plus using ADI normally lowers FTH so having 6000m for both boost settings (+350mm/+500mm) cannot be correct.

I am also certain that aerodynamic drag doesn't remain linear as speed increases so I'm skeptical that it can be used to accurately determine what speeds are attainable for a particular aircraft with any given horsepower. Same with propeller efficiency, as it also varies with RPM and air density.

So until I see more empirical data on this I would tend to agree with Hiroyuki Takeuchi concerning the Ki-84, who posted this information on the J-Aircraft website:

The Ha45 was designed to use 100 octane or at least 92 octane fuel but most IJA fuel was around 87 octane and probably even worse towards the end of the war. That means the motor had to be run on less boost and less power. Since the engine quality and airframe finish were also suffering, that all reflected upon performance. Writer Minoru Akimoto mentions that some Hayates in service conditions were lucky to achieve 600km/h (370mph). No wonder the 580km/h (360mph) Ki100 is often touted as the being better than the Ki84.

So while the Ki84 design had a 420mph potential, elements of reality (poor fuel, faulty engines, rought airframe finish, etc) often limited its performance to a lower level. May be the 624km/h (388mph) figure is about right after all.

Source: Ki-84 performance...so which is it? (Return to Faq)

And as far as the performance of the N1K2 is concerned, when taking into account different aircraft conditions and actual flight test data I suspect that maximum speed could vary around 20 mph (350-370 mph). A wartime maximum speed of 652 km/h (405 mph) is complete fantasy and shouldn't be considered as anywhere near the actual figure attainable during the war.

Like i said i stated performance with 92 octane fuel. No idea how they performed with 87 or lower octane fuel

 

[taly01]

Unfortunately we have to rely alot on partially translated Japanese books and websites, I think the 1946 US tests of J-aircraft are "interesting" but are more like best possible in best case conditions. Japanese sources seem to say around 25kph difference from N1K2-J to Ki-84 which seems entirely believable.

The Homare 21 boost went from military +350mm Hg to takeoff/emergency +500mm Hg (and some +100 rpm?), this is only a small increase and nothing like the boost jumps US and GER water-injected aircraft got (I don't have my boost conversion charts here).

I believe I read a US informal test of N1K1-J in Philippines and they said it got close to 400mph (before it was written off by landing gear collapsed). The N1K2-J was a much improved airplane but still a big lump compared to the Ki-84.

There is the post-war story of Japanese pilots ferrying N1K2-J been able to pull away from there Corsair F4U escorts, however there is alot detail missing from that account like altitude etc and what model Corsair etc.

 

[DarrenW]

There is the post-war story of Japanese pilots ferrying N1K2-J been able to pull away from there Corsair F4U escorts, however there is alot detail missing from that account like altitude etc and what model Corsair etc.

This excerpt is quoted from Genda's Blade (page 183):

On 16 October 1945, the time came to ferry flight to Yokosuka. LCdr Shiga met with Cdr Yamada and several Marine officers to discuss plans. One of the officers, a handsome man, appeared very familiar to Shiga. The plan was for a flight of three Shiden-Kais to be escorted by four Corsairs, with the Shiden-Kais in the middle, flanked by a pair of F4Us on the outside. The Americans ordered the Japanese to fly straight and level, otherwise they would be shot down. The 20mm cannon were reinstalled on the fighters, but obviously not loaded. Mechanics attached belly tanks for the long journey.

When all aircraft were airborne, the three Japanese pilots decided to unleash the full power of the Shiden-Kai. With no ammunition, the aircraft was a little lighter. Using high octane American aviation fuel, the Homare engine exhibited it's maximum power. As if on cue, the three ferry pilots gave full throttle and virtually left their escorts behind.

"The Corsairs raced after us at full speed!" recounted CPO Toshio Tanaka. "It was very thrilling and delightful! I gestured to them to speed up and try to catch us"

What I get from this exchange is that the Corsair pilots were set in cruise for the long flight and were caught completely off guard by the actions of the Shiden-Kai pilots. No where does it state that they outran the Corsairs. It's merely a playful story that is often taken out of context.

Speaking of pilot testimonials, here is an excerpt from page 86 of the same book concerning a mission report filed by VF-47 after a 16 April 1945 encounter with the 343rd Kokutai (VF-17 also participated in the action). The Japanese lost nine N1K2s with no losses to US Navy pilots (these figures have been verified):

Pilots of VF-47 who participated in this air battle came out of it with tremendous confidence in the F6F-5. They feel that their aircraft offers them tremendous advantage in firepower, armour protection and speed over the Japanese "Zeke", "Tojo", or "Tony". Even the F6Fs that were hit carried their pilots back to base. In contrast, the Japanese aircraft burned easily, often broke up when hit and seemed to lack effective firepower when in a good offensive position. Moreover, the F6F-5 easily matches the speed of these Japanese fighters. It is evident, however, that these Jap aircraft can out-turn the F6F.

Aside from the obvious misidentification of aircraft here, one can see that the performance of the N1K2 did not impress the Hellcat pilots, even with seasoned pilots at the controls. If the N1K2 could in fact reach 400 mph in level flight there would have been more positive feedback concerning it's performance IMHO.

For what it's worth, the F6Fs involved in this action would most likely have had wing pylons and rocket launchers so top speed with ADI would have been limited to about 380 mph at roughly 18,000 ft.