I have a B18A bottom end with a 1st gen B16A head. Should I run 2 o2 sensors, or just one? I noticed for N/A that 2 o2 sensors give far better gas mileage, so does the same apply for turbo? I am running a Zdyne ecu.

 

The ecu only needs one O2 sensor to function for the cloosed loop function, the secondary one is only for emissions (obd2).