Re: AFR - what's the ideal number ?
Ask him whether he was referring to cruise, economy AFR or max power.
Stoichiometric (on the $$ for economy cruise) is 14.7:1.........this would melt your pistons @ WOT, if it didn't ping to bits before it got there.
Full power requires a richer AFR to keep combustion temps low to avoid detonation. 13.2:1 is "supposed" to be the magic number, but this doesn't always seem true on dyno runs WRT various n/a engine combos......ie: little richer OK. Definitely don't go leaner than this.
FYI, late model EFI engines lean out to about 18-19:1 when cruising with the use of knock sensors. Wish mine did that :( $$$
393 Tremec TKO 9"