1. 2002/2003 wrx is fine with full exhaust/uppipe and no tune. You will gain some power but not as much as with a tune.

2. As long as the uppipe has no cat left in it, it will be perfectly fine. My friend gutted my stock uppipe on my old wrx wagon - worked perfect.

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http://webpages.charter.net/baraboo_...ppipe_fix.html