Ideal air-fuel mixture.. is it really 14.8?

imo 14+ is quite high. 12ish is a more of my area. but this is sordoff an opinion thing.

From my days as an aircraft mechanic, 12.5:1 was rich best power (added fuel helps cooling the intake air charge) and 13.5:1 was lean best power.

The 14.8:1 figure is best economy because it represents the perfect chemical balance of air and fuel.

Well the word stoich is actually short for stoichiometry or stoichiometric and it refers to the molar quantities of the reactants in a reaction (Octane and Oxygen) The stoichiometric point is where the most complete burn of both reactants occurs. This Air/Fuel Ratio of 14.7:1 is targeted because it produces the most power and creates the least amount of emissions. (i.e. the most complete consumption of the reactants)

Im not sure what you mean exactly by "those of us who run 02 sensors with gauges" are you talking about a wideband 02 sensor to measure actual AFR?

Here's the deal...you make more power the closer the AFR gets to stoich. however...that mixture becomes more sensitive to ignition timing. Poorly timed spark events in this case will lead to damaging detonation. (extreme residual pressure waves that occur AFTER spark ignition that bounce all around in the cylinder)

A richer AFR like 12:1 is much safer and the mixture is more tolerant to ignition timing changes. What you must realize here is that you have less oxygen in the reaction or fuel mixture. This means that there will be left over fuel that will not have enough oxygen to burn completely. All in all you have a safer setup, that is making less power and creating excess emissions.

For a drag only car this is fine...who cares about emissions, its all about a safe AFR that wont blow a hole through a piston. But Forced Induction cars are more sensitive to lean AFR's. With the huge amount of air being forced into the engine...the fuel delivery must be spot on and excessive in most cases or detonation is not only more likely but more damaging due to the higher cylinder pressures. Carb vs. EFI shouldnt make any different in terms of desired AFR. Do some reading...its interesting stuff.

I would say T idle 14.7 is fine. Once you start making power 12.5 is better. Especially if you are going to run a power adder. You do not want to go lean because holes develope in areas they shouldn't be.