I find the Western nomenclature slightly confusing and misleading and don't use it myself save for when posting information on here. I have seen the pre-production / trial aircraft referred to as a but not b in the literature I have but may have missed it / filtered it out. I have not seen a complete flight test equivalent to the US flight test made by the Japanese on any of the pre-production / trial prototypes. If you have such a thing would you please share it?
I have also been unable to find data which quantifies the thrust generated by the production aircraft's exhaust arrangement, if any. I know there were several formats of individual exits until the layout was settled on but do not think this was primarily intended to increase exhaust thrust but may have indeed been a side effect.
When I researched the Hayate (fairly deeply), about a year or so ago, I concluded based on horsepower and weights that we have what we can call the Ki-84-Ia Early Production version. This version uses the Ha-45-11 engine. This was neither a pre-production prototype nor a trial version, but the first standard production unit. The versions tested (by the TIAU) in the Philippines (two aircraft) were both Late Production Ki-84-Ia however, which had slightly more horsepower (Ha-45-21) and slightly less weight. The 21 was arguably the best Homare engine. Determining the point for the change in airframe numbers on the production line is rather difficult but the only surviving Ki-84 is one of these two with the Nakajima serial number 1446. This type was the basis for what some call the Ki-84-Ib, the Otsu, four cannon version, however we know the tested versions are Ko (2 cannon only) because of the gun gas ports in the fuselage and photographs of the instrument panel.
I think what you are 'effectively' asking for is a slightly later version of the Hayate than the one we currently have in the game. This would have approximately 2000 hp compared to our current version approximately 1800 hp. I have also seen some figures suggesting a 40 mph increase in top speed, but remain sceptical. Apart from an increase in top speed, acceleration, climb rate and whining would also increase.
On a slightly different issue, I am hoping that this manual can clear up some ambiguity about the flaps which came up during my research.
