I can understand your point and trying to help this guy figure out a maybe problem, or maybe not a problem, but my point was that he needs a min FF to get the full power On an O360 180 HP 200HP or any other piston powered engine, more than that will be for cooling, to much and you’ve caused another issue, to less fuel flow than needed to produce the rated power and you will not get to that HP no matter what you do to the engine. The manufacturer gives you what they need for FF for the additional cooling. In our world I dont think you can pull more HP out of a .5 pound of fuel than it has in it. If someone said they have an IO360 200HP that they have modified to burn only 10 gph on take off and 5gph per hour at 70% power I would call it a scam.
An IO360 200HP pushing 60% or 120 HP will burn 10gph or a O360 180HP pushing 67 % or 120HP will burn the same 10gph, or how about a 540 400HP, if it is ran at 30% or 120HP ( dont know why we would do this ) you would burn 10gph. It’s about the HP not the engine size.
I agree BTU is what is what energy it takes to raise one pound of water by 1 degree, and fuel has BTUs , but BFSC is directly realated to this question as it is fuel flow per hour (pounds per hour) divided by HP .