So SAFC works on hindering Air Flow metering to the ECU. So if you have 370cc injectors, and bump up to 550's. Then mathmatically your percentage change is 48.485% (50%) This is the max for the AFC unit. I knew 550's were all you could use(because someone told me. So you would set the AFC to -50% throughout the RPM range to get to stock. Then with your trusty A/f Gauge and knock counter make a pull and adjust accordingly then turn up boost and and fuel. Until you have your optimaly boost and a/f reading........let the discussion beginOh yea and by the way a stock s15 map shows a 10.8 A/f at max load at 6000 out to 8 500

That's not a safe way, experience with the 3sgte is that you never decrease anything below zero starting out with your base tune. Always use an adjustable fpr to set to stock base fuel pressure and tune with afc from there. Sometimes you may end up lowering stock fuel pressure just to get the car idling right and not run rich and then add fuel wherever you need to throughout the rpm band.

I set Fuel Pressure at 45psi. Going too high or low will not allow the injectors to function properly. Dont recommend going below 40psi or above 50psi. If your gonna tune with the SAFCII, using the stock ECU and SAFCII with 550cc injectors. Id probably lean out 20% to start and work from there. Keep at stock boost and tune very gradually for the AFR you desire. Be sure you have a Wideband O2 and not some cheap *** A/F Gauge. Keep AFR around 11.5-11.8 under WOT (Full Boost). Tune for around 12.5-13.0 under spool up @ WOT. Cruising and Light Throttle AFR shoud be around 14.0-15.0. Also remember the SAFCII is good for +/-50% of whatever the ECU is tuned for. So if you get an ECU Tune for 550cc Injectors, you can tune up to 825cc Injectors. I suggest Enthalpy Tune if you decide on a ECU Tune.