I am guessing I gained about 5-7 hp here, it make a big difference. This is not a car you would want to drive for any amount of time with this setup. Trust Louder than the OE muffler, much better sounding and quieter than the turbo style muffler. Least restrictive of all the systems tested so far. I can feel no real loss at the top with the cat back in.
Bottom end feels about the same.
Leave your cat in. Of course removing the cat is illegal on the street and will produce a resonance at particular rpms, even with an otherwise completely stock exhaust system. The OE muffler is of excellent design, of course it produces back pressure to reduce noise, but only above where non cammed SR20DEs poop out, or after 6500rpm. With or without a cat the stock muffler is producing results close to the turbo muffler, but MUCH quieter. The OE muffler seems to start increasing back pressure at about 5500 rpm on up.