Flowmaster 817666 Exhaust System Kit. Title: Flowmaster 817666 Cat-back System 409S - Dual Rear or Side Exit - Force II - Moderate Sound. Flowmaster's new Force II Cat-back exhaust system for the 2014-2018 Chevy Silverado and GMC Sierra 1500 trucks with 5.3L V8 (also fits 2019 classic models) is perfect for the person looking for a moderate sound level inside and outside of the truck, with all of the performance benefits that you would expect from Flowmaster.