So you're actually about .25 points lower if you're reading with the sniffer through stock cats.

 

Does that mean that my current tune is actually .25 richer than the sniffer shows?

 

Correct. It's not an exact science. The age of the catalytic converters, whether or not they are high flow or factory, all play a very small role in the difference. Typically, if you dyno a factory catted car with say 40,000 miles or less on it... an air fuel ratio of 12.5 would probably be closer to 12.3ish or slightly lower.

CR