I remember reading in the past the basic HP per gallon per hr
ratio, can you give it to me again.

  Ken Welter

.5 pounds of fuel per hour for each HP generated. BSFC for short.
Leaned 200 F degrees lean of peak at altitude  it is as low as .47
Full rich full power takeoff it is as much as  .6 to .65.
Not much different than any air cooled aircraft engine except
they won't run 200 degrees lean of peak.

Paul Lamar