Yes, but that assumes the engine was designed for a lower octane fuel but I don't think that is the case. I believe the American fuel simply allowed the engine to approach its maximum performance.
The engine was designed to use Japanese fuel they had at the time. The US tests were conducted with 92 octane fuel, Japanese had 92 octane fuel and they used it too.
I'm a bit confused as to your point Bighorn, you are saying the pair of aircraft tested in the Philippines had their engines modified by the Americans?
My statement was in regard to difference in performance figures, nothing else.
Now, what I'd like to see, if we have Ki-84-Ia in game, I'd like it to perform as Ki-84-Ia and not as Ki-84-a/b.
We should at least account for performance changes due to thrust augmentation which was good for 10mph in speed increase.
That is, our AH Frank should hit 400mph.
On the other hand, we have performance figures for Ki-84-Ia with Ha-45 type 21 from US tests. We should use those, because they are more reliable figures than figures used now for AH Frank (no guesswork needed).