KYOSTAR Valved Sport Catback Exhaust System for BMW F90 M5 S63 4.4T Twin-Turbo V8 Engine The KYOSTAR Valved Sport Catback Exhaust System is designed for 2018-2023 BMW F90 M5 models equipped with the S63 4.4T twin-turbo V8 engine. Developed as a performance exhaust upgrade, this system improves exhaust flow efficiency, reduces factory exhaust restriction, and enhances the aggressive V8 exhaust character with adjustable sound control through an integrated valve system.