I know you don't want 14.7 A/F ratio all the time no matter what. From discussions I've overheard over the years it seems like you want ratios below that to be safe and not detonate, particularly on turbo cars. I plan on getting the DIY wideband O2 sensor and learning how to tune with it. What are guidelines I should go by? What are "good" and "bad" A/F ratios for turbo applications? NA applications? And why are they good or bad? These things I do not yet understand, and a lot of people probably don't as well.

The guidelines and thumbrules I've seen are that for a N/A car, you start at about 13:1 at WOT, and for turbos around 12:1. Tune from there for maximum power, but try not to get much leaner. The extra fuel (richer than Stoich) is used to cool the cylinders. You need more fuel for a turbo engine because they inherently run hotter, not to mention reversion as a factor. Try not to get too rich, though, especially if you have the catalytic converter still in place. Too much unburned fuel, resting on the cat element, tends to autoignite, which causes cat-astrophic damage to same.

It's pretty simple, as above. I have no idea about ignition curves, though.