Well, Sir,
You must determine your own mindset. As you can see from the above, we've reestablished what you already know: generally, less yields less and more, more. Then, throw in all those little differences, and occassionally a more powerful rig will equal or use less fuel than a power train intended for economy. I know if I built a plane short of its power capacity, e.g., 320 when a 360 is mountable, intending to achieve Prius fuel economies, I would be mighty upset to be bested by a 360 ship at the pump. That's the risk you take trying to shave numbers in a race to minimums.
On the other hand, if initial costs and maintenance fears are not the true underlying issue, you can't easily retrofit a bigger rush down the runway and a bigger grin, as easily as clamping down the throttle for improved economy on a big engine already installed.
My -7 cruises above 10K at 7.2 gph and 193 from a O-360-A1A/dual EI/Superior sump, leaned a bit past peak. I also can easily slurp 10+ gph going 10 mph faster. Rocket friends who whine about running 15 inches to not leave me in the smog, achieve 10 gph from 540s that nominally are 15 gph engines.
My mindset? Strive for economy and stand a good chance of disappointment missing a nebulous target, or balls to the wall and so what if fuel costs are probably 5% more than what I might, maybe, could possibly, really ought to get from smaller displacement at the same speed?
The answer: YEE-HAH!
John Siebold
Boise, ID
