question about tuning the ecu.

Oh no...  What have I done.  That SCT tuner is a powerful tool - but you can fuck shit up if you do the wrong tweaks.

Overall - you dont want either "rich or lean".  You really want to achieve stoichiometric efficiency.  14.7:1.  On an NA street engine with bolt ons I wouldnt really want to see your AF's at over 13 during WOT.

The term "lean is mean" is a good rule of thumb. It means there isnt enough parts fuel to air.  Things get hot, and your promoting detonation, which will destroy engine bits with a quickness.

Too much fuel (rich condition) makes less HP, and if its really way to rich will wash down cylinder walls causing wear, and in extreme cases contaminate the oil in the crankcase, which can cause bearing failure/wear.

Overall tuning is a VERY complex art form.  You shouldn't fuck with that portion of the SCT until you have a wideband air/fuel gauge, and maybe a copy of EFI 101's tuning book.

can you get me that book?