DOES ANYONE KNOW IF IT IS POSSIBLE TO FIT AN ECU FROM A 96MY STI RA TO 93MY WRX . IF IT IS WILL IT PRODUCE MORE POWER OR JUST PROBLEMS

pretty sure it will not fit - and if it did, it would lead to problems - as your car has different components to an sti.

It would be a definite nono for me. The std engine may not be able to tolerate the temperatures that an STI block is subjected to. Also, the UK does not have 100RON pump gas, which is the main problem with running an STI there...

the 96 sti 2/3 has a 7500/8000rpm redlin whereas a wrx is 7000 too.

Not entirely sure the loom will fit!

Can't comment on the STI ecu but I have been told that a standard MY95/96 wrx ecu is a big improvement on your model (same as mine but not changed my ecu yet) and I think there is an improvement in power as well as they had 260 bhp rather than our 240. This is just what I have read in the past and NOT tested by myself so seek further advice if your interested