OE units will fit but they have design differences like some have cats others dont and diameter differences. They will "fit" each other however.
PERRIN has been known since our inception for the quality of our up-pipe. After all it was the first part we ever released and has been a leader in this market ever since. We have always used the finest materials and maintained proper size, shape and tolerances to make every installation a breeze. Made from 321 stainless steel and 1/2‚Äù flanges this is guaranteed not to warp, leak or fail. Power increases are consistent and strong. Our up-pipe is still one of the best and first ways to increase the power and throttle response on your Subaru.
obviously not mind blowing, but turbo spools sooner. I probably wouldn't mess with it because it's not worth it for me since I'm not trying to squeeze every bit of power out of the car (I'd much rather spend the money on something to make the car run safer or improve durability/rigidity), and I don't really care about a couple hundred rpms of spool.