14.68:1 is not rich nor lean. It is the perfect burn for gasoline and is the stoichiometric value GM sets all Z06s to in Closed Loop, which is the case of the Z06 is any throttle position below 48% at most rpms. A higher rpm, the throttle position is 25% to active open loop.
14.68 lbs of air for every 1 lb. of fuel is the chemically correct burn. Lean would be considered 14.8 or above, fuel enrichment would be considered any value below 14.68 or 14.5 and below.
11.5:1 is the open loop (fuel enrichment) value used by GM on the Z06 at full tilt (6,000 rpm), which most tuners consider very rich for a normally aspirated car.
Since gasoline needs 14.68 parts air to completely burn all the fuel in the cylinder, then running 11.5:1 sends all the excess fuel out into the atmosphere. Very Un-Green.
When I tune the Z06, we set the air fuel ratios leaner than the stock enrichment code, closer to 12.5:1. That is still fat, but much better for overall power.
Ethanol based fuels have a completely different stoichiometric value. For instance, E10 is 14:1, and E85 9.8:1. All of the newer cars adapter to the E10 fuel without any programming, but E85 needs the newer E38 ECM with the E80 table and MAF table to adapt to this Bio-Fuel.
It takes 3 gallons of E85 to trip the ECM as a refill event. This refill event causes the ECM to look at the short term fuel trims to see if they are in a new "learn" state. If so, the assumption is that a percentage of ethanol is in the tank, and the ECM adjusts to the fuel up to 90% ethanol.
The LS3 E38 ECM already has this table built into it, which means that GM is getting ready to get EPA approval for certain cars running Bio-Fuel. I do NOT recommend trying to run the LS3 and soon ZR1 in bio-fuel mode, since GM has not yet approved these cars to run the fuel, but it is coming soon.
My educated guess is that the LS9 will be a Flex Fuel car. It will have the LS3 style ECM onboard for sure, since the MAF tables go to 1822.12 g/sec vs. the current 512 g/sec airflow allowed in the E38 used by the Z06. So why is it necessary to supply code 3.5 times higher than the Z06 tables?
The Hz goes up to 15,850 Hz on the newer Hitachi Probe MAF sensor, so forced induction freaks, just wait. That kind of airflow table will support over 2000 HP!
Back to air fuel ratio. Your diablo thing is just providing you with the closed loop values, and they are at the perfect burn.