Graves Motorsports Ninja 400 2018 Carbon Cat-Back Slip-On exhaust. Our exhausts are hand-made in the USA for direct fitment to the Ninja 400 2018. This slip-on exhaust is new from the ground up with record breaking race developed features. Graves’ engineering develops precision products that are designed to outlook, outperform and outlast the competition. This product retains the OEM cat system and is intended for closed course competition use only.