Steve R:
There is an old axiom that "You cannot burn gasoline without adding AIR to it". Companies like Holley make a great living on that need....
It is easy to deliver gasoline, it is the AIR that is the difficult part of the equation. At 12.5:1 (AIR to FUEL) (A/F) ratio you are very certain to have enough fuel to match up with every exisiting oxygen molecule.
To make one horsepower per hour at 12.5:1, you need 6.25 pounds of air (12.5 x .5 = 6.25) (the .5 comes from the typical standard that it takes .5 pounds of fuel to produce one horsepower in the "standard internal combustion engine" Translated out a 400 HP engine running at the RPM to generate 400 HP would then consume 200 pounds of fuel per hour)
You can lean down the A/F ratios to 14:1 or 15:1 at cruise speeds and 14:1 to 17:1 at idle with the variance being the engine and ignition variables.
What I have seen, is that on ANY dyno, if you manually vary the A/F at any given operating speed, you will see that the BHP goes up as you richen up the mix and then will fall off when the mixture gets too rich. Running rich is for power, and durability to save valves and pistons. Running lean is for economy.
I hear that most EPA style tuned engines are in the 14.7:1 A/F ratio range.
For more data on this subject, I would recomend the fine booklet, Super Tuning Holley Carburetors by Alex Walordy. This is a great great resouce. Also the book, Desk Top Dynos by Larry Atherton. and lastly, How to Build and Tune Holley Carburetors by Des Hammill. These are all available on Amazon.com or often on ebay. The Desktop Dyno book comes with a computer program to do modeling. It is cool.
I smell that Turkey Cookin"
Wonder what the A/F ratio is in the OVEN.... Dope!