A Stage 1 tune is a recalibration of the factory ECU on a bone-stock car: boost targets rise modestly, ignition timing is optimized for your fuel, and the throttle and boost-control logic get sharpened. On most turbo Subarus that's worth a genuine 20-40 wheel horsepower and a much bigger midrange torque bump — with zero parts changed.
What it doesn't change matters just as much: fuel system limits, turbo efficiency, and the engine's mechanical margins are all still stock. A good Stage 1 map respects those ceilings. If a map promises Stage 2 numbers on stock hardware, it's spending your ringlands to get them.
Off-the-shelf (OTS) maps from reputable sources are safe as a starting point because they're deliberately conservative — they assume worst-case fuel and climate. A protune on your specific car almost always finds more power AND more safety margin, because it's calibrated to your actual engine, fuel, and altitude.
The honest ladder: OTS Stage 1 to get going, datalogs to confirm health (see the datalog guide in this section), then a protune when budget allows. Skipping the logging step is how people drive around on a knock-limited map for a year without knowing.
Tuning changes engine behavior. Numbers here are typical, not guaranteed — your fuel, climate, and hardware matter, and a professional calibration for your specific car always beats a generic map.