Tuning stages of the ecu and supporting mods. Stage 1 can just be a reflash of the ecu to get more tq, more hp, higher rev limits, and basically takes away the safe tune the manufacturer puts on for gas mileage and reliability. Stage 2 is usually another flash of the ecu and exhaust and possibly intake, and then they go from there. Subaru had about 8 different tuners with difference in stages so they all vary depending on tuner.What are these stages you speak of?
So on the Optima Turbo Stage 1 is an ecu tune with 35hp and 25lbs of tq gained. Stage 2 is downpipe, catback exahust, and intake optional. Stage 3 is stage 2 exhaust mods plus upgraded intercooler, spark plugs, and some other things in there.