I'm busy doing a speed/rev chart for all the ships and I've found that they have used simple fomulas for their speed/rev calculations as charts produced from all my timings show the same shape.
The Hiryu carrier's chart is a complete mess (it might be an oversight of the DEVs) so I played with it in Minitweaker to get it like the other carriers and found that I was limited to 'sliding' the Min/Mid/Max points up and down the chart, and was unable to do individual changes.
They might have the same story for the engine speed/fuel consumption.
