Performance EPROM, Porsche 911 C2/4 99-01 with 3.4l engine 996 chassis; ECU is silver box, (Black box is RACING DYNAMICS # 188.8.131.52) cust must ship ecu to rd; Our software upgrade provides your car with a 16 horsepower gain at the wheels and lots of improved torque and throttle response, The low-end torque and throttle response are improved and the drivability is smooth throughout the entire power band. The performance can be felt right away as your car will speed up through the revs quickly before reaching the raised rev limiter. Software upgrades prove them selves time and time again on the street as well as the track. You will need to give us the make and part number for your ECU box to confirm everything is ok. Then you overnight us your computer from your car and when we receive it that next day we will have our Engineer reprogram it and we will overnighted right back to you. Yes, you are down a couple days but the additional performance will be worth it.