How rich is too rich on a narrowband?

[brainfood]

When I am under load say in 4th or 5th lower rpms and the boost kicks in the narrow band gauge on the stock o2 goes to like 12.4 or so. Do I have a boost leak causing it to run rich or is this normal for a stock redtop sr?

[brokeAs240sx]

1) You probably already know this, but narrowband o2 sensor for afr is basically useless...

2) If your afr is 12.4:1 under boost, then you are not really running rich at all... that's just about right.

[brainfood]

Thanks I know the narrowband is by no means accurate in real time. I just wanted to make sure it was cool since I have a feeling my bov is leaking because the turbo spooling sound is pretty noticable but it could just be my intake, fmic, dp, and quiet exhaust.

[smelly240]

my car with no boost leaks was in the 11's a good bit richer than you - untuned.