I am reading a book in my spare time written by Sir Stanley Hooker.
Hooker redesigned the Merlin super charger making it better than the Allison. The fuel burn was listed in the book as 10.5 HP in 1939 for every pound of fuel/air consumed. To convert that to the poplar BSFC number works out at stoichiometric of 14.6  pounds of air and 1 pound of fuel means one must divide 10.5 HP by 15.6 I think.

That gives a BSFC of .67. Pounds of fuel burned per HP generated per hour. Not that great by todays standards.

If it were leaned to 16:1 the number would be .61.
The current rotary is .47 pounds of fuel burned per HP generated.

Check my arithmetic.

Paul Lamar