i have an 02 wrx and want to free up some power, i dont want to go full decat but what is the minimum i can get away with and still get through an mot ?
will an sti up pipe (no cat right ?) centre cat replacement and a prodrive sports cat work ?

 

That combo will work fine, and for an MOT a decat downpipe and leaving in the stock underfloor (with decat uppipe) is probably the best bang for buck as the PD/sportscat DP's are pricey.

Simon

 

Don't forget you'll need a remap as well if you decat a newage WRX, as it will overboost like mad otherwise.
Remap is likely to cost you circa 700 quid.
HTH