There's a reason they don't run draw throughs anymore...

Anyhoo, A/F and timing on a boosted engine depends alot on compression ratio, inlet air temp (right before intake valve), cylinder head chamber design, cylinder head material, and of course largely the fuel you run.

As a rule of thumb though low 12s is the absolute lean limit IMO for most home built boosted applications. And that's low boost IMO (6psi or less). Most people run in the high 11s, and when you start really pushing the boost (20+) more like high 10s.

Timing is the same, it's relative to how much boost and how well cool your inlet temps are. Rule of thumb though aim for 25 or less under boost. More boost and less octane means more timing retard.