Were to put a performance chip in a Nissan 240sx?

any performance chip will have to be soldered onto the ECU, the car's computer. this is located under the passenger side of the dashboard where the passenger's feet are located, on the right side. take off the paneling, and on some models it is under the carpet or even under the radio part of the dashboard. either way, wherever it is located, this is not something you can do yourself, especially if you dont even know where it goes. so you will have to have a mechanic do it for you, or even better you can take out the ECU and ship it to a company that will do it for you such as JWT, Jim Wolfe Technologies. look them up online.