IO540 fuel consumption (75%/best vs 60%/econ) power

I'm a bit confused with the chart provided in the IO540 ops manual:

-according to this chart fuel consumption at 75% Best Pwr Rating is approx.: 16.5 gph, but the table with Operating Conditions shows 15.0 gph?

-at 60% Econ. Pwr the fuel consumption of 12 gph seems to correspond with the Operating Conditions table.

Do I misinterpret the figures?



EDIT: My green vertical line is a little offset to the right.

I suspect they assume you will not run at a true best power mixture at cruise. Going a third of the way from best power to peak results is a VERY SMALL power reduction with a meaningful fuel flow reduction. They probably can't imagine anyone that would throw two gallons an hour at their engine for 5 extra horsepower and the 1 knot of speed it delivers and therefore provide the 15 GPH recommendation. Many users have a fuel flow gauge, yet have no experience in computing best power via EGT readings. I suspect the manual doesn't even tell you how many degrees ROP best power is. It is beyond most pilots and MANY don't have full EGT intstumentation.

My numbers

IO 540 c4b5 10:1 compression

This doesn't really apply to the 10. I have always run 21\19" lean of peak and get 8.8 gph in cruise. I put on one Sure Fly EI and got it down to 8.6 gph. This is on a Rocket.

Steve Barnes