I was just wondering why magazine Z28 tests and projects run lean on the dyno when GM supposedly programs the cars to run rich at wot?
With almost all tuners theoretically leaning out factory mixtures for power gains, why is it that vertually all the tests I've ever read about indicated that the car being tested was running lean? My 1995 Z28 has a handful of bolt-on modifications and feels like it really runs strong. Should I think it is still running factory rich at wot, or have the mods leaned it a bit? How could a free flow intake and exhaust lean the wot if the maf and oxygen sensors are working properly?

 

Stock programming sets the "target" A/F ratio in PE mode at about 11.7:1 (varies, based on several factors - but that's the one you'll see most often). That's generally richer than required for most engines to make peak HP/torque.... usually around 12.8-13.2:1. I've never seen a road test in a magazine that even mentioned A/F ratio on a stock setup, let alone one that said the car was running lean. If you mean testing of modified engines is showing a lean condition, that would have to do with the prgramming that was used for those modifications. I've seen many published and posted dyno tests for "stockish" engines running stock programming, and they are always on the fat side.

When you make mods that improves the breathing of your engine, it increases the mass air flow at any given RPM, and the PCM sees that extra air flow and increases the fuel mass flow rate. It's still using the same "target" A/F ratio that it calculated from the PE mode tables.