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The stock RB25 engines are very sensitive to air fuel ratio, it seems more so than usual. I have seem them lose rings at just 13.2:1 air fuel around 9psi.
You want that engine to be in the 11.5:1 range for best safety. It would make another 20~ horsepower if you run it at 12:1 but because you are using the SAFC and cannot directly pull timing I highly recommend you sacrifice the 20 horses for the sake of longeivity, install an AEM wideband about 3-4 feet away from the turbocharger, check for exhaust leaks, then tune the engine on a dyno so you can verify using the dyno's wideband that yours is reading correct. the dyno will read slightly leaner than yours, because of its location; You will want yours to say 11.4:1 and the dyno's to read about 11.8:1 across the board.
Dont let it creep up on you as the rpm passes 6,200, it will try, its not ok to let it creep up, keep the air fuel flat, even if it takes max adjustment and additional fuel pressure and dont take the engine over 7,000rpm for best longevity. Better to have an engine that puffs a little black smoke now and again than one that needs new piston rings.
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