Turbo XS UTEC Engine management has came up with a great concept in engine management For your WRX or STi It combines the features of a stand-alone engine management system with the simplicity of a piggyback system. (A Piggyback system is an engine management option that works in conjunction with your stock ECU. Depending on the manufacturer, this solution works by the piggyback unit controlling some engine management functions and the stock ECU controlling others). The Turbo XS UTEC enables complete programmable control over ignition timing, fuel, and boost, while allowing the factory ECU to maintain control over basic day-to-day functions. Functions like cold start, hot start, intake temperature compensation, AC compensation, and closed-loop fuel control signals. These are all managed by the factory ECU reducing your tuning time significantly while enhancing daily drivability.