I purchased an upgraded ECU from M2 Performance as more of a safety item rather than a performance modification. When modifications exceed an air intake and a cat back exhaust, a modified ECU becomes a must. After consulting with Brian for about a half hour or so, he set me up with an ECU that matched my modifications. At this point in time my ECU has been "maxed out". My injectors are operating at 90% at wide open throttle. Above 85% can result in overheated injectors and become a reliability issue. He also informed me that although a common modification for the fuel system is an upgraded fuel pump, it is not completely necessary. If the stock pump is operating properly, it will supply enough fuel to the injectors. There is just less room for error with the stock setup. My next step is a stand alone computer, additional injectors, and an upgraded fuel pump. I can't wait.
Along with the fuel being remapped in the upgraded ECU, the timing is also fine tuned to work with the new fuel mapping. The new redline with the upgraded ECU is approximately 8300 RPM's. However, HP does takes a severe dive after 7000.
Last but perhaps most important is the elimination of the stock boost/ fuel cut. The stock ECU will cut fuel to the rotors if boost exceeds 11psi. The will cause a temporarily lean condition in the engine which in turn could blow an apex seal. The upgrade eliminates this feature so that increased boost levels could be achieved. The ECU is also supposed to set the boost at 13psi, but I already had a boost controller installed so I can't verify how well the upgraded ECU controls boost with the stock boost pill installed.
Approximate Performance Gain:
Upgraded ECU - 40+ HP (depends upon boost setting)