i bought a spoon n1 back box for my integra,,,, had to take it off......way to loud esp about 3000rpm... motor way driving was killing me!!!!!!! 105 dB.
I think custom made without cat and muffler, just straight longer pipe with a loop design like Mugen would be cheapest, loudest and give good gains. Just don't go over 2.25in as stock exhuast is 2.0in. You won't loose torque but make power and torque.