MILLTEK SSXNI003 Secondary Cat-back Quad 127mm GT127 ECA NISSAN GT-R R35Description MILLTEK SSXNI003 Secondary Cat back Quad 127mm GT127 ECA NISSAN GT R R35 The Milltek Sport Secondary Cat Back systems replace all OEM exhaust components located after the secondary catalyst. These systems are designed for those seeking improved sound and aesthetics. Each system is a direct replacement for the original exhaust and is available in multiple configurations, allowing the owner to select the desired increase in exhaust volume or