I see all the kits have it but none say what it does...so what does it do?

 

On the DOHC setups, the blue box trims map voltage to allow the use of 310cc injectors, has a boost limiter cut setting so that the ecu never sees boost, and pulses the injectors longer for additional fuel. The sohc blue box that comes with the 92-95 kit does the same except for trimming map voltage for larger injectors.

 

so with the box, you don't need to have FMU...?

 

No you wont. I would recommend an emanage rather than the blue box.