14.7 to 1 AFR is not clever to anything thank light load cruising and idle. For a N/A motor i would aim for 12,5 to 1 for high loading (70+ TPS, 4500+ rpm) and ~13,5 for an all out racing engine that i could monitor any time. (As an example, an EP3 type R at 12-12,3 will be around 215-220hp, at 13,5 it will be around 230-235) For a turbo motor i would go for 11.5 for high loading, around 13 in light acceleration (still in vacuum or ~0.1 to 0.2bar boost) and 14.7 at light cruising (highway 65mph, 3500rpm). In a all out race turbo motor i'd go for 12.5 AFR as i could regularly monitor it and check for problems. Also have you ever installed an UEGO in a stock engine (4efte)? Idle is 14.5-15 Light cruising is 14-14.5 Light acceleration is ~13.5 going to ~12 after 3500-4000 rpms Full power is 10.5 to 11. If boost is upped (let say 0,85bar) then it will go richer than 10 in full power. Full pull from 2000rpms will be 12.5 till 3500, around 11 till 5000 and 10,5 and richer till the limiter.